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Traditional IP routing emphasizes on forwarding traffic to the destination as fast as possible. As a result, the routing protocols find out the least-cost route according to its metric to each destination in the network and every router forwards the packet based on the destination IP address and packets are forwarded hop-by-hop. Thus, traditional IP routing does not consider the available bandwidth of the link. This can cause some links to be over-utilized compared to others and bandwidth is not efficiently utilized. Traffic Engineering (TE) is used when the problems result from inefficient mapping of traffic streams onto the network resources. Traffic engineering allows you to control the path that data packets follow and moves traffic flows from congested links to non-congested links that would not be possible by the automatically computed destination-based shortest path.
Multiprotocol Label Switching (MPLS) with its label switching capabilities, eliminates the need for an IP route look-up and creates a virtual circuit (VC) switching function, allowing enterprises the same performance on their IP-based network services as with those delivered over traditional networks such as Frame Relay or Asynchronous Transfer Mode (ATM). MPLS traffic engineering (MPLS-TE) relies on the MPLS backbone to replicate and expand upon the TE capabilities of Layer 2 ATM and Frame Relay networks.
MPLS-TE learns the topology and resources available in a network and then maps traffic flows to particular paths based on resource requirements and network resources such as bandwidth. MPLS-TE builds a unidirectional tunnel from a source to a destination in the form of a label switched path (LSP), which is then used to forward traffic. The point where the tunnel begins is called the tunnel headend or tunnel source, and the node where the tunnel ends is called the tunnel tailend or tunnel destination. A router through which the tunnel passes is called the mid-point of the tunnel.
MPLS uses extensions to a link-state based Interior Gateway Protocol (IGP), such as Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF). MPLS calculates TE tunnels at the LSP head based on required and available resources (constraint-based routing). If configured, the IGP automatically routes the traffic onto these LSPs. Typically, a packet that crosses the MPLS-TE backbone travels on a single LSP that connects the ingress point to the egress point. MPLS TE automatically establishes and maintains the LSPs across the MPLS network by using the Resource Reservation Protocol (RSVP).
 Note |
Combination of unlabelled paths protected by labelled paths is not supported. |
These prerequisites are required to implement MPLS TE:
Router that runs Cisco IOS XR software .
Installed composite mini-image and the MPLS package, or a full composite image.
IGP activated.
In MPLS traffic engineering, IGP extensions flood the TE information across the network. Once the IGP distributes the link attributes and bandwidth information, the headend router calculates the best path from head to tail for the MPLS-TE tunnel. This path can also be configured explicitly. Once the path is calculated, RSVP-TE is used to set up the TE LSP (Labeled Switch Path).
To forward the traffic, you can configure autoroute, forward adjacency, or static routing. The autoroute feature announces the routes assigned by the tailend router and its downstream routes to the routing table of the headend router and the tunnel is considered as a directly connected link to the tunnel.
If forward adjacency is enabled, MPLS-TE tunnel is advertised as a link in an IGP network with the link's cost associated with it. Routers outside of the TE domain can see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.
MPLS-TE provides protection mechanism known as fast reroute to minimize packet loss during a failure. For fast reroute, you need to create back up tunnels. The autotunnel backup feature enables a router to dynamically build backup tunnels when they are needed instead of pre-configuring each backup tunnel and then assign the backup tunnel to the protected interfaces.
DiffServ Aware Traffic Engineering (DS-TE) enables you to configure multiple bandwidth constraints on an MPLS-enabled interface to support various classes of service (CoS). These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint.
The MPLS traffic engineering auto-tunnel mesh feature allows you to set up full mesh of TE tunnels automatically with a minimal set of MPLS traffic engineering configurations. The MPLS-TE auto bandwidth feature allows you to automatically adjusts bandwidth based on traffic patterns without traffic disruption.
The MPLS-TE interarea tunneling feature allows you to establish TE tunnels spanning multiple Interior Gateway Protocol (IGP) areas and levels, thus eliminating the requirement that headend and tailend routers should reside in a single area.
For detailed information about MPLS-TE features, see the MPLS-TE Features - Details topic.
Note |
MPLS-TE Nonstop Routing (NSR) is enabled by default without any user configuration and cannot be disabled. MPLS-TE NSR means the application is in hot-standby mode and standby MPLS-TE instance is ready to take over from the active instance quickly on RP failover. Note that the MPLS-TE does not do routing. If there is standby card available then the MPLS-TE instance is in a hot-standby position. The following output shows the status of MPLS-TE NSR: During any issues with the MPLS-TE, the NSR on the router gets affected which is displayed in the show redundancy output as follows: |
MPLS-TE automatically establishes and maintains label switched paths (LSPs) across the backbone by using RSVP. The path that an LSP uses is determined by the LSP resource requirements and network resources, such as bandwidth. Available resources are flooded by extensions to a link state based Interior Gateway Protocol (IGP). MPLS-TE tunnels are calculated at the LSP headend router, based on a fit between the required and available resources (constraint-based routing). The IGP automatically routes the traffic to these LSPs. Typically, a packet crossing the MPLS-TE backbone travels on a single LSP that connects the ingress point to the egress point.
The following sections describe the components of MPLS-TE:
From a Layer 2 standpoint, an MPLS tunnel interface represents the headend of an LSP. It is configured with a set of resource requirements, such as bandwidth and media requirements, and priority. From a Layer 3 standpoint, an LSP tunnel interface is the headend of a unidirectional virtual link to the tunnel destination.
This calculation module operates at the LSP headend. The module determines a path to use for an LSP. The path calculation uses a link-state database containing flooded topology and resource information.
RSVP operates at each LSP hop and is used to signal and maintain LSPs based on the calculated path.
This module operates at each LSP hop, performs link call admission on the RSVP signaling messages, and keep track on topology and resource information to be flooded.
Either Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF) can be used as IGPs. These IGPs are used to globally flood topology and resource information from the link management module.
This forwarding mechanism provides routers with a Layer 2-like ability to direct traffic across multiple hops of the LSP established by RSVP signaling.
MPLS-TE preemption consists of freeing the resources of an established LSP, and assigning them to a new LSP. The freeing of resources causes a traffic disruption to the LSP that is being preempted. Soft preemption is an extension to the RSVP-TE protocol to minimize and even eliminate such traffic disruption over the preempted LSP.
The soft-preemption feature attempts to preempt the LSPs in a graceful manner to minimize or eliminate traffic loss. However, the link might be over-subscribed for a period of time.
In a network that implements soft preemption, zero traffic loss is achieved in this manner:
When signaling a new LSP, the ingress router indicates to all the intermediate nodes that the existing LSP is to be softly preempted, in case its resources are needed and is to be reassigned.
When a given intermediate node needs to soft-preempt the existing LSP, it sends a new or special path error (preemption pending) to the ingress router. The intermediate node does not dismantle the LSP and maintains its state.
When the ingress router receives the path error (preemption pending) from the intermediate node, it immediately starts a re-optimization that avoids the link that caused the preemption.
When the re-optimization is complete, the ingress router tears down the soft-preempted LSP.
The soft-preemption over FRR backup tunnels feature enables to move LSP traffic over the backup tunnels when the LSP is soft- preempted. MPLS TE tunnel soft-preemption allows removal of extra TE traffic in a graceful manner, by giving the preempted LSP a grace period to move away from the link. Though this mechanism saves the traffic of the preempted LSP from being dropped, this might cause traffic drops due to congestion as more bandwidth is reserved on the link than what is available. When the soft-preemption over FRR backup tunnel is enabled, the traffic of the preempted LSP is moved onto the FRR backup, if it is available and ready. This way, the capacity of the backup tunnel is used to remove the potential congestion that might be caused by soft-preemption.
There are few limitations to the configured SRLG feature:
The exclude-address and exclude-srlg options are not allowed in the IP explicit path strict-address network.
Whenever SRLG values are modified after tunnels are signaled, they are verified dynamically in the next path verification cycle.
This section describes the RSVP-TE Dark Bandwidth Accounting feature that allows for the co-existence of non-zero bandwidth RSVP-TE tunnels and Segment Routing (SR) in the same network domain. This feature measures dark bandwidth traffic and accounts for it in the RSVP-TE bandwidth reservations to avoid overbooking the links in the network.
Dark bandwidth is the actual utilization of the link by the subset of the traffic that is not explicitly admission controlled by RSVP-TE. Dark bandwidth is not considered during path computation and admission control for distributed RSVP-TE LSPs.
In this solution, SR is assumed to be the main source of dark bandwidth on the links in the network. In addition, SR traffic is considered to have a higher priority than any other traffic transported by RSVP-TE LSPs. Therefore, the bandwidth consumed by SR effectively reduces the link bandwidth available to RSVP-TE LSPs.
The RSVP-TE Dark Bandwidth Accounting feature consists of the following:
The measurement of SR traffic on interfaces via new per-interface aggregate SR counters
The calculation of dark bandwidth rate based on the measured SR traffic statistics
The calculation of the RSVP-TE effective maximum reservable bandwidth (BMRe).
The BMRe is used for the purpose of pre-emption as well as advertisement (flooding) via IGP. A threshold is evaluated before triggering flooding.
The statistics collector process (statsD) is responsible for returning statistics counters for each feature. For each traffic engineering (TE)-enabled interface, the TE process collects new SR bandwidth rate statistics (samples) from the statsD process, within a specified sampling interval. These samples are collected over a period of time called an application interval.
After each application interval, the average value of the collected rate samples is used to compute the dark bandwidth rate and the BMRe rate.
The following example shows how the BMRe is computed (assuming a link capacity of 10Gbps and a configured BMR [BMRc] of 90%):
Link capacity = 10Gbps
BMRc = RSVP percentage of link capacity = 9Gbps
Calculated dark bandwidth rate = 2Gpbs
BMRe = 7Gbps
In this example, the bandwidth available for RSVP-TE LSP admission is 7Gbps. This value is flooded in the network if the flooding threshold is crossed.
Note |
When you change the RSVP bandwidth percentage configuration or when the bundle capacity changes due to bundle-member state change, TE accounts for the dark bandwidth when new bandwidth values are advertised. |
Note |
The measured dark bandwidth can be increased or decreased based on a configurable adjustment factor. |
When the dark bandwidth rate increases for a link, it will lower the BMR of that link, which might trigger preemption of the RSVP-TE LSPs. Preemption consists of freeing the resources of an established LSP, and assigning them to a new LSP. The freeing of resources causes a traffic disruption to the LSP that is being preempted.
This section contains the following topics:
The Point-to-Multipoint (P2MP) Resource Reservation Protocol-Traffic Engineering (RSVP-TE) solution allows service providers to implement IP multicast applications, such as IPTV and real-time video, broadcast over the MPLS label switch network. The RSVP-TE protocol is extended to signal point-to-point (P2P) and P2MP label switched paths (LSPs) across the MPLS network.
Note |
|
By using RSVP-TE extensions as defined in RFC 4875, multiple subLSPs are signaled for a given TE source. The P2MP tunnel is considered as a set of Source-to-Leaf (S2L) subLSPs that connect the TE source to multiple leaf Provider Edge (PE) nodes.
At the TE source, the ingress point of the P2MP-TE tunnel, IP multicast traffic is encapsulated with a unique MPLS label, which is associated with the P2MP-TE tunnel. The traffic continues to be label-switched in the P2MP tree. If needed, the labeled packet is replicated at branch nodes along the P2MP tree. When the labeled packet reaches the egress leaf (PE) node, the MPLS label is removed and forwarded onto the IP multicast tree across the PE-CE link.
To enable end-to-end IP multicast connectivity, RSVP is used in the MPLS-core for P2MP-TE signaling and PIM is used for PE-CE link signaling.
All edge routers are running PIM-SSM or Source-Specific Multicast (SSM) to exchange multicast routing information with the directly-connected Customer Edge (CE) routers.
In the MPLS network, RSVP P2MP-TE replaces PIM as the tree building mechanism, RSVP-TE grafts or prunes a given P2MP tree when the end-points are added or removed in the TE source configuration (explicit user operation).
These are the definitions for Point-to-Multipoint (P2MP) tunnels. Cisco 8000 Series routers only support the role of a mid-point.
Configures the node in which Label Switched Path (LSP) signaling is initiated.
Specifies the transit node in which LSP signaling is processed (for example, not a source or receiver).
Specifies the node in which LSP signaling ends.
Specifies the node in which packet replication is performed.
Specifies the P2MP-TE LSP segment that runs from the source to one leaf.
P2MP RSVP-TE (RFC 4875) is supported. RFC 4875 is based on nonaggregate signaling; for example, per S2L signaling. Only P2MP LSP is supported.
The interface tunnel-mte command identifies the P2MP interface type.
P2MP tunnel setup is supported with label replication.
Explicit routing is supported by using under utilized links.
Reoptimization is supported by calculating a better set of paths to the destination with no traffic loss.
Note |
Per-S2L reoptimization is not supported. |
IPv4 and IPv6 payloads are supported.
IPv4 and IPv6 multicast forwarding are supported on a P2MP tunnel interface through a static IGMP and MLD group configuration.
Both IP multicast and P2MP Label Switch Multicast (LSM) coexist in the same network; therefore, both use the same forwarding plane (LFIB or MPLS Forwarding Infrastructure [MFI]).
P2MP label replication supports only Source-Specific Multicast (SSM) traffic. SSM configuration supports the default value, none.
Static mapping for multicast groups to the P2MP-TE tunnel is required.
Single point of traffic control ensures that signaling and path engineering parameters (for example, protection and diversity) are configured only at the TE source node.
Ability to configure explicit paths to enable optimized traffic distribution and prevention of single point of failures in the network.
Link protection of MPLS-labeled traffic traversing branch paths of the P2MP-TE tree.
Ability to do bandwidth Admission Control (AC) during set up and signaling of P2MP-TE paths in the MPLS network.
RSVP-TE signals a P2MP tunnel base that is based on a manual configuration. If all Source-to-Leaf (S2L)s use an explicit path, the P2MP tunnel creates a static tree that follows a predefined path based on a constraint such as a deterministic Label Switched Path (LSP). If the S2L uses a dynamic path, RSVP-TE creates a P2MP tunnel base on the best path in the RSVP-TE topology. RSVP-TE supports bandwidth reservation for constraint-based routing.
RSVP-TE distributes stream information in which the topology tree does not change often (where the source and receivers are). For example, large scale video distribution between major sites is suitable for a subset of multicast applications. Because multicast traffic is already in the tunnel, the RSVP-TE tree is protected as long as you build a backup path.
The P2MP tunnel is signaled by the dynamic and explicit path option in the IGP intra area. Only interArea and interAS, which are used for the P2MP tunnels, are signaled by the verbatim path option.
The Point-to-Multipoint Label Switch Path (P2MP LSP) has only a single root, which is the Ingress Label Switch Router (LSR). The P2MP LSP is created based on a receiver that is connected to the Egress LSR. The Egress LSR initiates the creation of the tree (for example, tunnel grafting or pruning is done by performing an individual sub-LSP operation) by creating the Forwarding Equivalency Class (FEC) and Opaque Value.
Note |
Grafting and pruning operate on a per destination basis. |
The Opaque Value contains the stream information that uniquely identifies the tree to the root. To receive label switched multicast packets, the Egress Provider Edge (PE) indicates to the upstream router (the next hop closest to the root) which label it uses for the multicast source by applying the label mapping message.
The upstream router does not need to have any knowledge of the source; it needs only the received FEC to identify the correct P2MP LSP. If the upstream router does not have any FEC state, it creates it and installs the assigned downstream outgoing label into the label forwarding table. If the upstream router is not the root of the tree, it must forward the label mapping message to the next hop upstream. This process is repeated hop-by-hop until the root is reached.
By using downstream allocation, the router that wants to receive the multicast traffic assigns the label for it. The label request, which is sent to the upstream router, is similar to an unsolicited label mapping (that is, the upstream does not request it). The upstream router that receives that label mapping uses the specific label to send multicast packets downstream to the receiver. The advantage is that the router, which allocates the labels, does not get into a situation where it has the same label for two different multicast sources. This is because it manages its own label space allocation locally.
P2MP tunnels are signaled by using the dynamic and explicit path-options in an IGP intra area. InterArea cases for P2MP tunnels are signaled by the verbatim path option.
Path options for P2MP tunnels are individually configured for each sub-LSP. Only one path option per sub-LSP (destination) is allowed. You can choose whether the corresponding sub-LSP is dynamically or explicitly routed. For the explicit option, you can configure the verbatim path option to bypass the topology database lookup and verification for the specified destination.
Both dynamic and explicit path options are supported on a per destination basis by using the path-option (P2MP-TE) command. In addition, you can combine both path options.
Explicit Path Option
Configures the intermediate hops that are traversed by a sub-LSP going from the TE source to the egress MPLS node. Although an explicit path configuration enables granular control sub-LSP paths in an MPLS network, multiple explicit paths are configured for specific network topologies with a limited number of (equal cost) links or paths.
Dynamic Path Option
Computes the IGP path of a P2MP tree sub-LSP that is based on the OSPF and ISIS algorithm. The TE source is dynamically calculated based on the IGP topology.
Note |
Dynamic path option can only compute fully-diverse standby paths. While, explicit path option supports partially diverse standby paths as well. |
Dynamic path calculation for each sub-LSP uses the same path parameters as those for the path calculation of regular point-to-point TE tunnels. As part of the sub-LSP path calculation, the link resource (bandwidth) is included, which is flooded throughout the MPLS network through the existing RSVP-TE extensions to OSPF and ISIS. Instead of dynamic calculated paths, explicit paths are also configured for one or more sub-LSPs that are associated with the P2MP-TE tunnel.
OSPF or ISIS are used for each destination.
TE topology and tunnel constraints are used to input the path calculation.
Tunnel constraints such as affinity, bandwidth, and priorities are used for all destinations in a tunnel.
Path calculation yields an explicit route to each destination.
The static path calculation does not require any new extensions to IGP to advertise link availability.
Explicit path is required for every destination.
Offline path calculation is used.
TE topology database is not needed.
If the topology changes, reoptimization is not required.
The Point-to-Multipoint (P2MP) implicit null feature enables the forwarding of unicast traffic over P2MP tunnels. This feature is enabled by default and requires no configuration.
In a P2MP tunnel, the tailend router signals the implicit null label to the midpoint router. If the given MPI leg of the P2MP tunnel is implicit null capable (where the penultimate router is capable to do penultimate hop popping), the FIB (Forwarding Information Base) creates two NRLDI (Non Recursive Load Distribution Index) entries, one for forwarding the IPv6 labeled packets, and the other for non-labeled IPv4 unicast traffic.
The headend and the tailend routers handle the unicast traffic arriving on the P2MP tunnel. The midpoint router forwards the unicast traffic to its bud and tailend routers.
The use of implicit null at the end of a tunnel is called penultimate hop popping (PHP). The FIB entry for the tunnel on the PHP router shows a "pop label" as the outgoing label.
In some cases, it could be that the packets have two or three or more labels in the label stack. Then the implicit null label used at the tailend router would signal the penultimate hop router to pop one label and send the labeled packet with one label less to the tailend router. Then the tailend router does not have to perform two label lookups. The use of the implicit null label does not mean that all labels of the label stack must be removed; only one label is "popped" off (remove the top label on the stack). In any case, the use of the implicit null label prevents the tailend router from performing two lookups.
Restriction - The P2MP implicit null feature may cause multicast traffic drop with implicit null label on the tailend routers. This is because the P2MP implicit null feature does not support forwarding of multicast traffic when no label is received on the tailend router.
MPLS-TE requires co-ordination among several global neighbor routers. RSVP, MPLS-TE and IGP are configured on all routers and interfaces in the MPLS traffic engineering network. Explicit path and TE tunnel interfaces are configured only on the head-end routers. MPLS-TE requires some basic configuration tasks explained in this section.
Building MPLS-TE topology, sets up the environment for creating MPLS-TE tunnels. This procedure includes the basic node and interface configuration for enabling MPLS-TE. To perform constraint-based routing, you need to enable OSPF or IS-IS as IGP extension.
Before you start to build the MPLS-TE topology, the following pre-requisites are required:
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
Enable RSVP on the port interface.
This example enables MPLS-TE on a node and then specifies the interface that is part of the MPLS-TE. Here, OSPF is used as the IGP extension protocol for information distribution.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# interface hundredGigE 0/0/0/3
Router(config)# router ospf area 1
Router(config-ospf)# area 0
Router(config-ospf-ar)# mpls traffic-eng
Router(config-ospf-ar)# interface hundredGigE 0/0/0/3
Router(config-ospf-ar-if)# exit
Router(config-ospf)# mpls traffic-eng router-id 192.168.70.1
Router(config)# commitThis example enables MPLS-TE on a node and then specifies the interface that is part of the MPLS-TE. Here, IS-IS is used as the IGP extension protocol for information distribution.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# interface hundredGigE 0/0/0/3
Router(config)# router isis 1
Router(config-isis)# net 47.0001.0000.0000.0002.00
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# mpls traffic-eng level 1
Router(config-isis-af)# exit
Router(config-isis)# interface hundredGigE 0/0/0/3
Router(config-isis-if)# exit
Router(config)# commitAutomatic bandwidth allows you to dynamically adjust bandwidth reservation based on measured traffic. MPLS-TE automatic bandwidth monitors the traffic rate on a tunnel interface and resizes the bandwidth on the tunnel interface to align it closely with the traffic in the tunnel. MPLS-TE automatic bandwidth is configured on individual Label Switched Paths (LSPs) at every headend router.
Adjustment Threshold - It is defined as a percentage of the current tunnel bandwidth and an absolute (minimum) bandwidth. Both thresholds must be fulfilled for the automatic bandwidth to resignal the tunnel. The tunnel bandwidth is resized only if the difference between the largest sample output rate and the current tunnel bandwidth is larger than the adjustment thresholds.
For example, assume that the automatic bandwidth is enabled on a tunnel in which the highest observed bandwidth B is 30 Mbps. Also, assume that the tunnel was initially configured for 45 Mbps. Therefore, the difference is 15 mbit/s. Now, assuming the default adjustment thresholds of 10% and 10kbps, the tunnel is signaled with 30 Mbps when the application timer expires. This is because 10% of 45Mbit/s is 4.5 Mbit/s, which is smaller than 15 Mbit/s. The absolute threshold, which by default is 10kbps, is also crossed.
The following table specifies the parameters that can be configured as part of automatic bandwidth configuration.
|
Bandwidth Parameters |
Description |
|---|---|
|
Application frequency |
Configures how often the tunnel bandwidths changed for each tunnel. The default value is 24 hours. |
|
Bandwidth limit |
Configures the minimum and maximum automatic bandwidth to set on a tunnel. |
|
Bandwidth collection frequency |
Enables bandwidth collection without adjusting the automatic bandwidth. The default value is 5 minutes. |
|
Overflow threshold |
Configures tunnel overflow detection. |
|
Adjustment threshold |
Configures the tunnel-bandwidth change threshold to trigger an adjustment. |
This example enables automatic bandwidth on MPLS-TE tunnel interface and configure the following automatic bandwidth variables.
Application frequency
Bandwidth limit
Adjustment threshold
Overflow detection
Router# configure
Router(config)# interface tunnel-te 1
Router(config-if)# auto-bw
Router(config-if-tunte-autobw)# application 1000
Router(config-if-tunte-autobw)# bw-limit min 30 max 1000
Router(config-if-tunte-autobw)# adjustment-threshold 50 min 800
Router(config-if-tunte-autobw)# overflow threshold 100 limit 1
Router(config)# commit
Verify the automatic bandwidth configuration using the show mpls traffic-eng tunnels auto-bw brief command.
Router# show mpls traffic-eng tunnels auto-bw brief
Tunnel LSP Last appl Requested Signalled Highest Application
Name ID BW(kbps) BW(kbps) BW(kbps) BW(kbps) Time Left
-------------- ------ ---------- ---------- ---------- ---------- --------------
tunnel-te1 5 500 300 420 1h 10m|
Feature Name |
Release Information |
Feature Description |
|---|---|---|
|
Configuring Automatic Capacity With Load-Interval Configuration |
Release 7.3.3 |
With this feature, you can enable the load-interval configuration for a main tunnel's clones, along with the automatic capacity feature. |
The auto-bandwidth feature resizes MPLS-TE tunnels based on traffic loads. Multiple auto-bandwidth tunnels can be created for balancing traffic loads and redundancy.
The auto-capacity feature is an extension of the auto-bandwidth feature. With auto-capacity, for an auto-bandwidth enabled MPLS-TE tunnel, you can enable automatic creation and deletion of tunnels based on real-time capacity demands. These tunnels are called clones. For a main TE tunnel, you can specify the minimum and maximum number of clones, and allocate a nominal tunnel bandwidth value. Clones are automatically added to, or removed from, the main TE tunnel, based on the nominal bandwidth.
Consider the auto-capacity configuration example:
Router(config)# mpls traffic-eng
Router(config-mpls-te)# named-tunnels tunnel-te YOW2YZZ
Router(config-te-tun-name)# load-interval 90
Router(config-te-tun-name)# auto-bw
Router(config-mpls-te-tun-autobw)# auto-capacity
Router(config-mpls-te-tun-autobw)# commit
retries to establish the LSPs. The timeout range is 1 to 600 seconds.
The auto-capacity function is disabled by default. Since auto-bandwidth and auto-capacity functions are inter-related, these are the corresponding changes in behavior:
When you enable auto-capacity, it is associated with a specific TE-tunnel, under the auto-bandwidth function. When you disable auto-bandwidth, auto-capacity is also disabled.
If the load interval is enabled for the main tunnel, it is automatically applied to its clones too. For a main tunnel, if the auto-capacity feature is enabled but a load interval is not enabled, the clones’ load interval value is set to a default of 300 seconds.
Splitting and Merging Tunnels
When there is a change in demand for bandwidth, MPLS-TE adds or reduces the number of tunnels and resizes the bandwidth of all the tunnels. It verifies these rules during this activity.
The number of tunnels between the headend-tailend router pair is within the specified range, and the bandwidth per tunnel is within the auto-bandwidth range.
The (Bandwidth-per-tunnel)*(Number-of-Tunnels) >= Total-tunnel-bandwidth requirement.
While Rule 1 is enforced, MPLS-TE attempts to enforce Rule 2.
When the split requirement is met, and the maximum number of clones is not reached, at least one extra clone is added.
When the merge requirement is met, and the minimum number of clones is not reached, at least one clone is removed
The nominal bandwidth value is used to balance the requirements of: (a) Number of tunnels and (b) Bandwidth for each tunnel. This helps in avoiding a merging or splitting instance at the next application event.
/* Automatic Capacity Function */
Router# configure
Router(config)# mpls traffic-eng
The auto-capacity feature is only valid for the main tunnel YOW2YZZ, with reference to which, clones are created or removed.
Router(config-mpls-te)# named-tunnels tunnel-te YOW2YZZ
Router(config-te-tun-name)# auto-bw auto-capacity
MPLS-TE maintains the number of clones between 1 and 7. Including the main tunnel YOW2YZZ, the tunnel count range is between 2 and 8.
Router(config-te-tun-autocapacity)# max-clones 7
Router(config-te-tun-autocapacity)# min-clones 1
The nominal-bandwidth option is used for specifying the target bandwidth based on which MPLS-TE calculates the number of required tunnels.
Router(config-te-tun-autocapacity)# nominal-bandwidth 2000000
MPLS-TE also uses the merge-bandwidth and split-bandwidth values when implementing the auto-capacity feature.
Router(config-te-tun-autocapacity)# merge-bandwidth 1000000
Router(config-te-tun-autocapacity)# split-bandwidth 3000000
Router(config-te-tun-autocapacity)# commit
/* View the Auto-Capacity Feature Configuration */
Router# show mpls traffic-eng tunnels name YOW2YZZ
Name: YOW2YZZ Ifhandle:0xf000014
..
Config Parameters:
..
Load-interval: 300 seconds ..
Auto-Capacity: Enabled
Minimum Clones: 1; Maximium Clones: 7
Nominal BW: 2000000 kbps; Merge BW: 1000000 kbps; Split BW: 3000000 kbps
Statistics:
Splits: 0; Merges: 0
Clones Created: 1; Clones Deleted: 0
Clones High Watermark: 1
Number of clones: 1
Clone: YOW2YZZ-1
Created: Thu Jan 27 13:55:06 2022; State: down
..
An MPLS-TE tunnel sets up labeled connectivity and provides dynamic bandwidth capacity between its endpoints. The auto-bandwidth function addresses the dynamic bandwidth capacity demands by resizing the MPLS-TE tunnels based on the measured traffic loads. However, many customers require multiple auto-bandwidth tunnels between two endpoints for load balancing and redundancy. The auto-bandwidth bundle TE++ function is an extension of the auto-bandwidth feature, and provides this support. When the aggregate bandwidth between the endpoints changes, MPLS-TE creates new tunnels or removes existing tunnels to load balance the traffic.
When MPLS-TE automatically creates new tunnels to meet increasing bandwidth demands, they are called clones. The original tunnel and its clones collectively form a set. The clones inherit the properties of the main tunnel, except for the user-configured load-interval value. You can specify an upper limit and lower limit on the number of clones.
Splitting is the process of creating a new clone. When the bandwidth of a tunnel crosses the split bandwidth value, MPLS-TE creates a clone.
The following figure explains how MPLS-TE creates clones when the split bandwidth exceeds the configured value.
Merging is the process of removing a clone. If the bandwidth goes below the merge bandwidth value in a set of tunnels, MPLS-TE removes a clone.
The following figure explains how MPLS-TE removes clones when the bandwidth falls below the merge bandwidth value.
There are multiple ways to load-share the aggregate bandwidth demand among the tunnels in a set. An algorithm chooses the pair that satisfies the aggregate bandwidth requirements. You can configure a nominal bandwidth to guide the algorithm that determines the average bandwidth of the tunnels. If you don't configure, MPLS-TE uses the average of the split bandwidth and merge bandwidth values as the nominal bandwidth.
The following guidelines and restrictions apply for the auto-bandwidth bundle TE++ feature.
This feature only supports named tunnels, and doesn't support tunnel-te interfaces.
The range for the lower limit on the number of clones is 0–63. The default value is 0. The upper limit range is 1–63. The default value is 63.
Configure the following parameters:
min-clones : Specifies the minimum number of clones that the original tunnel can create.
max-clones : Specifies the maximum number of clones that the original tunnel can create.
nominal-bandwidth : Specifies the average bandwidth for computing the number of tunnels to satisfy the overall demand.
split-bandwidth : Specifies the bandwidth for splitting the original tunnel. If the tunnel bandwidth exceeds the configured split bandwidth, MPLS-TE creates clones.
merge-bandwidth : Specifies the bandwidth for merging clones with the original tunnel. If the bandwidth goes below the merge bandwidth value, MPLS-TE removes the clones.
Configuration Example: Named MPLS-TE Tunnel
This example shows how to configure the auto-bandwidth bundle TE++ feature for a named MPLS-TE tunnel.
Here, the lower and upper limits on the number of clones are two and four, respectively. The bandwidth size for splitting and merging are 200 kbps and 100 kbps, respectively.
Router(config)# mpls traffic-eng
Router(config-mpls-te)# named-tunnels
Router(config-te-named-tunnels)# tunnel-te xyz
Router(config-te-tun-name)# auto-bw
Router(config-mpls-te-tun-autobw)# auto-capacity
Router(config-te-tun-autocapacity)# min-clones 2
Router(config-te-tun-autocapacity)# max-clones 4
Router(config-te-tun-autocapacity)# nominal-bandwidth 150
Router(config-te-tun-autocapacity)# split-bandwidth 200
Router(config-te-tun-autocapacity)# merge-bandwidth 100
The MPLS Traffic Engineering Auto-Tunnel Backup feature enables a router to dynamically build backup tunnels on the interfaces that are configured with MPLS TE tunnels instead of building MPLS-TE tunnels statically.
The MPLS-TE Auto-Tunnel Backup feature has these benefits:
Backup tunnels are built automatically, eliminating the need for users to pre-configure each backup tunnel and then assign the backup tunnel to the protected interface.
Protection is expanded—FRR does not protect IP traffic that is not using the TE tunnel or Label Distribution Protocol (LDP) labels that are not using the TE tunnel.
The TE attribute-set template that specifies a set of TE tunnel attributes, is locally configured at the headend of auto-tunnels. The control plane triggers the automatic provisioning of a corresponding TE tunnel, whose characteristics are specified in the respective attribute-set.
This example configures Auto-Tunnel backup on an interface and specifies the attribute-set template for the auto tunnels. In this example, unused backup tunnels are removed every 20 minutes using a timer and also the range of tunnel interface numbers are specified.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# interface HundredGigabitEthernet 0/0/0/3
Router(config-mpls-te-if)# auto-tunnel backup
Router(config-mpls-te-if-auto-backup)# attribute-set ab
Router(config-mpls-te)# auto-tunnel backup timers removal unused 20
Router(config-mpls-te)# auto-tunnel backup tunnel-id min 6000 max 6500
Router(config-mpls-te)# commit
Router# show mpls traffic-eng tunnels brief
TUNNEL NAME DESTINATION STATUS STATE
tunnel-te0 200.0.0.3 up up
tunnel-te1 200.0.0.3 up up
tunnel-te2 200.0.0.3 up up
tunnel-te50 200.0.0.3 up up
*tunnel-te60 200.0.0.3 up up
*tunnel-te70 200.0.0.3 up up
*tunnel-te80 200.0.0.3 up up To remove all the backup autotunnels, perform this task.
Router# clear mpls traffic-eng auto-tunnel backup unused all
Use the show mpls traffic-eng auto-tunnel summary command to verify MPLS-TE autotunnel information, including the ones removed.
The MPLS-TE auto-tunnel mesh (auto-mesh) feature allows you to set up full mesh of TE Point-to-Point (P2P) tunnels automatically with a minimal set of MPLS traffic engineering configurations. You can configure one or more mesh-groups and each mesh-group requires a destination-list (IPv4 prefix-list) listing destinations, which are used as destinations for creating tunnels for that mesh-group.
You can configure MPLS-TE auto-mesh type attribute-sets (templates) and associate them to mesh-groups. Label Switching Routers (LSRs) can create tunnels using the tunnel properties defined in this attribute-set.
Auto-Tunnel mesh configuration minimizes the initial configuration of the network. You can configure tunnel properties template and mesh-groups or destination-lists on TE LSRs that further creates full mesh of TE tunnels between those LSRs. It eliminates the need to reconfigure each existing TE LSR in order to establish a full mesh of TE tunnels whenever a new TE LSR is added in the network.
This example configures an auto-tunnel mesh group and specifies the attributes for the tunnels in the mesh-group.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# auto-tunnel mesh
Router(config-mpls-te-auto-mesh)# tunnel-id min 1000 max 2000
Router(config-mpls-te-auto-mesh)# group 10
Router(config-mpls-te-auto-mesh-group)# attribute-set 10
Router(config-mpls-te-auto-mesh-group)# destination-list dl-65
Router(config-mpls-te)# attribute-set auto-mesh 10
Router(config-mpls-te-attribute-set)# autoroute announce
Router(config-mpls-te-attribute-set)# auto-bw collect-bw-only
Router(config)# commit
Verify the auto-tunnel mesh configuration using the show mpls traffic-eng auto-tunnel mesh command.
Router# show mpls traffic-eng auto-tunnel mesh
Auto-tunnel Mesh Global Configuration:
Unused removal timeout: 1h 0m 0s
Configured tunnel number range: 1000-2000
Auto-tunnel Mesh Groups Summary:
Mesh Groups count: 1
Mesh Groups Destinations count: 3
Mesh Groups Tunnels count:
3 created, 3 up, 0 down, 0 FRR enabled
Mesh Group: 10 (3 Destinations)
Status: Enabled
Attribute-set: 10
Destination-list: dl-65 (Not a prefix-list)
Recreate timer: Not running
Destination Tunnel ID State Unused timer
---------------- ----------- ------- ------------
192.168.0.2 1000 up Not running
192.168.0.3 1001 up Not running
192.168.0.4 1002 up Not running
Displayed 3 tunnels, 3 up, 0 down, 0 FRR enabled
Auto-mesh Cumulative Counters:
Last cleared: Wed Oct 3 12:56:37 2015 (02:39:07 ago)
Total
Created: 3
Connected: 0
Removed (unused): 0
Removed (in use): 0
Range exceeded: 0Fast reroute (FRR) provides link protection to LSPs enabling the traffic carried by LSPs that encounter a failed link to be rerouted around the failure. The reroute decision is controlled locally by the router connected to the failed link. The headend router on the tunnel is notified of the link failure through IGP or through RSVP. When it is notified of a link failure, the headend router attempts to establish a new LSP that bypasses the failure. This provides a path to reestablish links that fail, providing protection to data transfer. The path of the backup tunnel can be an IP explicit path, a dynamically calculated path, or a semi-dynamic path. For detailed conceptual information on fast reroute, see the MPLS-TE Features - Details topic.
The following prerequisites are required to create an MPLS-TE tunnel:
You must have a router ID for the neighboring router.
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID to the routers, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
This example configures fast reroute on an MPLS-TE tunnel. Here, tunnel-te 2 is configured as the back-up tunnel. You can use the protected-by command to configure path protection for an explicit path that is protected by another path.
Router# configure
Router(config)# interface tunnel-te 1
Router(config-if)# fast-reroute
Router(config-if)# exit
Router(config)# mpls traffic-eng
Router(config-mpls-te)# interface HundredGigabitEthernet 0/0/0/3
Router(config-mpls-te-if)# backup-path tunnel-te 2
Router(config)# interface tunnel-te 2
Router(config-if)# backup-bw global-pool 5000
Router(config-if)# ipv4 unnumbered Loopback0
Router(config-if)# destination 192.168.92.125
Router(config-if)# path-option l explicit name backup-path protected by 10
Router(config-if)# path-option l0 dynamic
Router(config)# commit
Use the show mpls traffic-eng fast-reroute database command to verify the fast reroute configuration.
Router# show mpls traffic-eng fast-reroute database
Tunnel head FRR information:
Tunnel Out intf/label FRR intf/label Status
---------- ---------------- ---------------- -------
tt4000 HundredGigabitEthernet 0/0/0/3:34 tt1000:34 Ready
tt4001 HundredGigabitEthernet 0/0/0/3:35 tt1001:35 Ready
tt4002 HundredGigabitEthernet 0/0/0/3:36 tt1001:36 Ready
MPLS-TE Flexible Name-based Tunnel Constraints provides a simplified and more flexible means of configuring link attributes and path affinities to compute paths for the MPLS-TE tunnels.
In traditional TE, links are configured with attribute-flags that are flooded with TE link-state parameters using Interior Gateway Protocols (IGPs), such as Open Shortest Path First (OSPF).
MPLS-TE Flexible Name-based Tunnel Constraints lets you assign, or map, up to 32 color names for affinity and attribute-flag attributes instead of 32-bit hexadecimal numbers. After mappings are defined, the attributes can be referred to by the corresponding color name.
This example shows assigning a how to associate a tunnel with affinity constraints.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# affinity-map red 1
Router(config-mpls-te)# interface HundredGigabitEthernet 0/0/0/3
Router(config-mpls-te-if)# attribute-names red
Router(config)# interface tunnel-te 2
Router(config-if)# affinity include red
Router(config)# commitPerform this task to configure forwarding path in the MPLS-TE interface.
Router # configure
Router(config)# interface tunnel-te 1
Router(config-if)# forward-class 1
Router(config-if)# exit
Router(config)# commit
IETF DS-TE mode uses IETF-defined extensions for RSVP and IGP. This mode interoperates with third-party vendor equipment. IETF mode supports multiple bandwidth constraint models, including Russian Doll Model (RDM) and Maximum Allocation Model (MAM), both with two bandwidth pools.
This example configures an IETF DS-TE tunnel using MAM.
Router# configure
Router(config)# rsvp interface HundredGigabitEthernet 0/0/0/3
Router(config-rsvp-if)# bandwidth mam max-reservable-bw 1000 bc0 600 bc1 400
Router(config-rsvp-if)# exit
Router(config)# mpls traffic-eng
Router(config-mpls-te)# ds-te mode ietf
Router(config-mpls-te)# ds-te bc-model mam
Router(config-mpls-te)# exit
Router(config)# interface tunnel-te 2
Router(config-if)# signalled bandwidth sub-pool 10
Router(config)# commit
Use the show mpls traffic-eng topology command to verify the IETF DS-TE tunnel using MAM configuration.
IETF DS-TE mode uses IETF-defined extensions for RSVP and IGP. This mode interoperates with third-party vendor equipment.
IETF mode supports multiple bandwidth constraint models, including Russian Doll Model (RDM) and Maximum Allocation Model (MAM), both with two bandwidth pools. In an IETF DS-TE network, identical bandwidth constraint models must be configured on all nodes.
The following prerequisites are required to create a IETF mode DS-TE tunnel using RDM:
You must have a router ID for the neighboring router.
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID to the routers, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
This example configures an IETF DS-TE tunnel using RDM.
Router# configure
Router(config)# rsvp interface HundredGigabitEthernet 0/0/0/3
Router(config-rsvp-if)# bandwidth rdm 100 150
Router(config-rsvp-if)# exit
Router(config)# mpls traffic-eng
Router(config-mpls-te)# ds-te mode ietf
Router(config-mpls-te)# exit
Router(config)# interface tunnel-te 2
Router(config-if)# signalled bandwidth sub-pool 10 class-type 1
Router(config)# commit
Use the show mpls traffic-eng topology command to verify the IETF DS-TE tunnel using RDM configuration.
The MPLS TE Interarea Tunneling feature allows you to establish MPLS TE tunnels that span multiple Interior Gateway Protocol (IGP) areas and levels. This feature removes the restriction that required the tunnel headend and tailend routers both to be in the same area. The IGP can be either Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF).To configure an inter-area tunnel, you specify on the headend router a loosely routed explicit path for the tunnel label switched path (LSP) that identifies each area border router (ABR) the LSP should traverse using the next-address loose command. The headend router and the ABRs along the specified explicit path expand the loose hops, each computing the path segment to the next ABR or tunnel destination.
This example configures an IPv4 explicit path with ABR configured as loose address on the headend router.
Router# configure
Router(config)# explicit-path name interarea1
Router(config-expl-path)# index1 next-address loose ipv4 unicast 172.16.255.129
Router(config-expl-path)# index 2 next-address loose ipv4 unicast 172.16.255.131
Router(config)# interface tunnel-te1
Router(config-if)# ipv4 unnumbered Loopback0
Router(config-if)# destination 172.16.255.2
Router(config-if)# path-option 10 explicit name interarea1
Router(config)# commit
Path protection provides an end-to-end failure recovery mechanism for MPLS-TE tunnels. A secondary Label Switched Path (LSP) is established, in advance, to provide failure protection for the protected LSP that is carrying a tunnel's TE traffic. When there is a failure on the protected LSP, the source router immediately enables the secondary LSP to temporarily carry the tunnel's traffic. Failover is triggered by a RSVP error message sent to the LSP head end. Once the head end received this error message, it switches over to the secondary tunnel. If there is a failure on the secondary LSP, the tunnel no longer has path protection until the failure along the secondary path is cleared. Path protection can be used within a single area (OSPF or IS-IS), external BGP [eBGP], and static routes. Both the explicit and dynamic path-options are supported for the MPLS-TE path protection feature. You should make sure that the same attributes or bandwidth requirements are configured on the protected option.
The following prerequisites are required for enabling path protection.
You should ensure that your network supports MPLS-TE, Cisco Express Forwarding, and Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF).
You should configure MPLS-TE on the routers.
This example configures how to configure path protection for a mpls-te tunnel. The primary path-option should be present to configure path protection. In this configuration, R1 is the headend router and R3 is the tailend router for the tunnel while R2 and R4 are mid-point routers. In this example, 6 explicit paths and 1 dynamic path is created for path protection. You can have upto 8 path protection options for a primary path.
Note |
Path-protection through user-specified path-options is not supported and the protected-by is used specifically only for numbered tunnels and unavailable for named-tunnels. |
Router # configure
Router(config)# interface tunnel-te 0
Router(config-if)# destination 192.168.3.3
Router(config-if)# ipv4 unnumbered Loopback0
Router(config-if)# autoroute announce
Router(config-if)# path-protection
Router(config-if)# path-option 1 explicit name r1-r2-r3-00 protected-by 2
Router(config-if)# path-option 2 explicit name r1-r2-r3-01 protected-by 3
Router(config-if)# path-option 3 explicit name r1-r4-r3-01 protected-by 4
Router(config-if)# path-option 4 explicit name r1-r3-00 protected-by 5
Router(config-if)# path-option 5 explicit name r1-r2-r4-r3-00 protected-by 6
Router(config-if)# path-option 6 explicit name r1-r4-r2-r3-00 protected-by 7
Router(config-if)# path-option 7 dynamic
Router(config-if)# exit
Router(config)# commit
Use the show mpls traffic-eng tunnels command to verify the MPLS-TE path protection configuration.
Router# show mpls traffic-eng tunnels 0
Name: tunnel-te0 Destination: 192.168.92.125 Ifhandle:0x8007d34
Signalled-Name: router
Status:
Admin: up Oper: up Path: valid Signalling: connected
path option 1, type explicit r1-r2-r3-00 (Basis for Setup, path weight 2)
Protected-by PO index: 2
path option 2, type explicit r1-r2-r3-01 (Basis for Standby, path weight 2)
Protected-by PO index: 3
path option 3, type explicit r1-r4-r3-01
Protected-by PO index: 4
path option 4, type explicit r1-r3-00
Protected-by PO index: 5
path option 5, type explicit r1-r2-r4-r3-00
Protected-by PO index: 6
path option 6, type explicit r1-r4-r2-r3-00
Protected-by PO index: 7
path option 7, type dynamic
G-PID: 0x0800 (derived from egress interface properties)
Bandwidth Requested: 0 kbps CT0
Creation Time: Fri Oct 13 15:05:28 2017 (01:19:11 ago)
Config Parameters:
Bandwidth: 0 kbps (CT0) Priority: 7 7 Affinity: 0x0/0xffff
Metric Type: TE (global)
Path Selection:
Tiebreaker: Min-fill (default)
Hop-limit: disabled
Cost-limit: disabled
Delay-limit: disabled
Path-invalidation timeout: 10000 msec (default), Action: Tear (default)
AutoRoute: enabled LockDown: disabled Policy class: not set
Forward class: 0 (not enabled)
Forwarding-Adjacency: disabled
Autoroute Destinations: 0
Loadshare: 0 equal loadshares
Auto-bw: disabled
Fast Reroute: Disabled, Protection Desired: None
Path Protection: Enabled
BFD Fast Detection: Disabled
Reoptimization after affinity failure: Enabled
Soft Preemption: Disabled
History:
Tunnel has been up for: 01:14:13 (since Fri Oct 13 15:10:26 UTC 2017)
Current LSP:
Uptime: 01:14:13 (since Fri Oct 13 15:10:26 UTC 2017)
Reopt. LSP:
Last Failure:
LSP not signalled, identical to the [CURRENT] LSP
Date/Time: Fri Oct 13 15:08:41 UTC 2017 [01:15:58 ago]
Standby Reopt LSP:
Last Failure:
LSP not signalled, identical to the [STANDBY] LSP
Date/Time: Fri Oct 13 15:08:41 UTC 2017 [01:15:58 ago]
First Destination Failed: 192.3.3.3
Prior LSP:
ID: 8 Path Option: 1
Removal Trigger: path protection switchover
Standby LSP:
Uptime: 01:13:56 (since Fri Oct 13 15:10:43 UTC 2017)
Path info (OSPF 1 area 0):
Node hop count: 2
Hop0: 192.168.1.2
Hop1: 192.168.3.1
Hop2: 192.168.3.2
Hop3: 192.168.3.3
Standby LSP Path info (OSPF 1 area 0), Oper State: Up :
Node hop count: 2
Hop0: 192.168.2.2
Hop1: 192.168.3.1
Hop2: 192.168.3.2
Hop3: 192.168.3.3
Displayed 1 (of 4001) heads, 0 (of 0) midpoints, 0 (of 0) tails
Displayed 1 up, 0 down, 0 recovering, 0 recovered heads
The backup tunnels that bypass only a single link of the LSP path are referred as Next Hop (NHOP) backup tunnels because they terminate at the LSP's next hop beyond the point of failure. They protect LSPs, if a link along their path fails, by rerouting the LSP traffic to the next hop, thus bypassing the failed link.
This example configures next hop backup tunnel on an interface and specifies the attribute-set template for the auto tunnels. In this example, unused backup tunnels are removed every 20 minutes using a timer and also the range of tunnel interface numbers are specified.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# interface HundredGigabitEthernet 0/0/0/3
Router(config-mpls-te-if)# auto-tunnel backup nhop-only
Router(config-mpls-te-if-auto-backup)# attribute-set ab
Router(config-mpls-te)# auto-tunnel backup timers removal unused 20
Router(config-mpls-te)# auto-tunnel backup tunnel-id min 6000 max 6500
Router(config)# commit
For P2MP tunnels, a Cisco 8000 Series router supports the mid-point router function, and does not support source or receiver functions. To know how to configure a source or receiver (destination) router in a P2MP tunnel, refer the MPLS configuration guide for the corresponding platform.
The P2MP-TE Auto-tunnels feature enables dynamic creation and management of P2MP auto-tunnels for the transport of VPLS traffic on Cisco IOS XR Software. The P2MP-TE auto-tunnel configuration is disabled by default. Use the auto-tunnel p2mp tunnel-id command to enable a P2MP-TE Auto-tunnel. This configures the tunnel ID range that can be allocated to P2MP auto-tunnels. This also determines the maximum number of P2MP auto-tunnels that can be created.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# auto-tunnel p2mp
Router(config-te-auto-p2mp)# tunnel-id min 10000 max 11000
Router(config-te-auto-p2mp)# commit
Perform this task to enable the soft-preemption feature in the MPLS TE configuration mode. By default, this feature is disabled. You can configure the soft-preemption feature for each node. It has to be explicitly enabled for each node.
If soft-preemption is enabled, the head-end node tracks whether an LSP desires the soft-preemption treatment. However, when a soft-preemption feature is disabled on a node, this node continues to track all LSPs desiring soft-preemption. This is needed in a case when soft-preemption is re-enabled, TE will have the property of the existing LSPs without any re-signaling.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# soft-preemption
Router(config-soft-preemption)# timeout 100
Router(config-soft-preemption)# commit
Perform this task to enable the soft-preemption feature on a MPLS TE tunnel. By default, this feature is disabled. It has to be explicitly enabled.
When soft preemption is enabled on a tunnel, a path-modify message is sent for the current LSP, reopt LSP, path protection LSP, and current LSP in FRR active state, with the soft preemption desired property.
Router# configure
Router(config)# interface tunnel-te 10
Router(config-if)# soft-preemption
Router(config-if)# commit
Before enabling soft-preemption over FRR backup, ensure that you enable soft-preemption, and activate the FRR backup tunnel.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# soft-preemption frr-rewrite
Router(config-mpls-te)# commit
Regular traffic engineering does not provide bandwidth guarantees to different traffic classes. A single bandwidth constraint is used in regular TE that is shared by all traffic. MPLS DS-TE enables you to configure multiple bandwidth constraints on an MPLS-enabled interface. These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint. Cisco IOS XR software supports two DS-TE modes: Pre-standard and IETF. Pre-standard DS-TE uses the Cisco proprietary mechanisms for RSVP signaling and IGP advertisements. This DS-TE mode does not interoperate with third-party vendor equipment. Pre-standard DS-TE is enabled only after configuring the sub-pool bandwidth values on MPLS-enabled interfaces.
Pre-standard Diff-Serve TE mode supports a single bandwidth constraint model a Russian Doll Model (RDM) with two bandwidth pools: global-pool and sub-pool.
The following prerequisites are required to configure a Pre-standard DS-TE tunnel.
You must have a router ID for the neighboring router.
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID to the routers, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
This example configures a pre-standard DS-TE tunnel.
Router# configure
Router(config)# rsvp interface HundredGigabitEthernet 0/0/0/3
Router(config-rsvp-if)# bandwidth 100 150 sub-pool 50
Router(config-rsvp-if)# exit
Router(config)# interface tunnel-te 2
Router(config-if)# signalled bandwidth sub-pool 10
Router(config)# commit
Use the show mpls traffic-eng topology command to verify the pre-standard DS-TE tunnel configuration.
Shared Risk Link Groups (SRLG) in MPLS traffic engineering refer to situations in which links in a network share common resources. These links have a shared risk, and that is when one link fails, other links in the group might fail too.
OSPF and IS-IS flood the SRLG value information (including other TE link attributes such as bandwidth availability and affinity) using a sub-type length value (sub-TLV), so that all routers in the network have the SRLG information for each link.
MPLS-TE SRLG feature enhances backup tunnel path selection by avoiding using links that are in the same SRLG as the interfaces it is protecting while creating backup tunnels.
This example creates a backup tunnel and excludes the protected node IP address from the explicit path.
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# interface HundredGigabitEthernet 0/0/0/3
Router(config-mpls-te-if)# backup-path tunnl-te 2
Router(config-mpls-te-if)# exit
Router(config)# interface tunnel-te 2
Router(config-if)# ipv4 unnumbered Loopback0
Router(config-if)# path-option 1 explicit name backup-srlg
Router(config-if)# destination 192.168.92.125
Router(config-if)# exit
Router(config)# explicit-path name backup-srlg-nodep
Router(config-if)# index 1 exclude-address 192.168.91.1
Router(config-if)# index 1 exclude-srlg 192.168.92.2
Router(config)# commit
There are few limitations to the configured SRLG feature:
The exclude-address and exclude-srlg options are not allowed in the IP explicit path strict-address network.
Whenever SRLG values are modified after tunnels are signaled, they are verified dynamically in the next path verification cycle.
Creating an MPLS-TE tunnel is a process of customizing the traffic engineering to fit your network topology. The MPLS-TE tunnel is created at the headend router. You need to specify the destination and path of the TE LSP.
To steer traffic through the tunnel, you can use the following ways:
Static Routing
Autoroute Announce
Forwarding Adjacency
The following prerequisites are required to create an MPLS-TE tunnel:
You must have a router ID for the neighboring router.
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID to the routers, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
This example configures an MPLS-TE tunnel on the headend router with a destination IP address 192.168.92.125. The bandwidth for the tunnel, path-option, and forwarding parameters of the tunnel are also configured. You can use static routing, autoroute announce or forwarding adjacency to steer traffic through the tunnel.
Router# configure
Router(config)# interface tunnel-te 1
Router(config-if)# destination 192.168.92.125
Router(config-if)# ipv4 unnumbered Loopback0
Router(config-if)# path-option 1 dynamic
Router(config-if)# autoroute announce | forwarding-adjacency
Router(config-if)# signalled-bandwidth 100
Router(config)# commit
Verify the configuration of MPLS-TE tunnel using the following command.
Router# show mpls traffic-engineering tunnels brief
Signalling Summary:
LSP Tunnels Process: running
RSVP Process: running
Forwarding: enabled
Periodic reoptimization: every 3600 seconds, next in 2538 seconds
Periodic FRR Promotion: every 300 seconds, next in 38 seconds
Auto-bw enabled tunnels: 0 (disabled)
TUNNEL NAME DESTINATION STATUS STATE
tunnel-te1 192.168.92.125 up up
Displayed 1 up, 0 down, 0 recovering, 0 recovered heads If the IGP calculation on a router results in an equal cost multipath (ECMP) scenario where next-hop interfaces are a mix of MPLS-TE tunnels and physical interfaces, you may want to ensure that a TE tunnel is preferred. Consider this topology:
All links in the network have a metric of 5.
To offload a congested link between R3 and R4, an MPLS-TE tunnel is created from R3 to R2.
If the metric of the tunnel is also 5, traffic from R3 to R5 is load-balanced between the tunnel and the physical R3-R4 link.
To ensure that the MPLS-TE tunnel is preferred in such scenarios, configure the autoroute metric command on the tunnel interface. The modified metric is applied in the routing information base (RIB), and the tunnel is preferred over the physical path of the same metric. Sample configuration:
Router# configure
Router(config)# interface tunnel-te 1
Router(config-if)# autoroute metric relative -1
The autoroute metric command syntax is autoroute metric {absolute|relative} value
absolute enables the absolute metric mode, for a metric range between 1 and 2147483647.
relative enables the relative metric mode, for a metric range between -10 and 10, including zero.
Note |
|
To enable RSVP-TE Dark Bandwidth Accounting feature, perform the following steps:
Enable per-interface aggregate SR counters.
Configure TE dark bandwidth accounting.
| Command or Action | Purpose | |||||
|---|---|---|---|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
||||
|
Step 2 |
hw-module profile cef dark-bw enable Example: |
Enables per-interface aggregate SR counters for all interfaces on the router.
|
||||
|
Step 3 |
mpls traffic-eng Example: |
Enters MPLS TE configuration mode. |
||||
|
Step 4 |
bandwidth-accounting Example: |
Enables RSVP-TE dark bandwidth accounting and enters bandwidth accounting configuration mode. |
||||
|
Step 5 |
application interval seconds Example: |
Configures the length of the application interval in seconds. At the end of application interval, dark bandwidth rates are computed and applied to all RSVP-TE enabled interfaces. If the interval is reconfigured while the timer is running, the new value is compared to the time remaining for the running timer. The timer is adjusted so that the lower of these two values is used for this interval. The subsequent interval will use the newly configured value.
Range is from 90 to 1800. The default value is 180. |
||||
|
Step 6 |
application enforced Example: |
Enables enforcement of the calculated BMRe rate. |
||||
|
Step 7 |
sampling-interval seconds Example: |
Configures the length of the sampling interval in seconds. The dark bandwidth rate is collected from the statistics collector process (statsD) at the end of each sampling interval for each TE link. If the interval is reconfigured while the timer is running, the new value is compared to the time remaining for the running timer. The timer is adjusted so that the lower of these two values is used for this interval. The subsequent interval will use the newly configured value. Range is from 10 to 600. The default is 60. |
||||
|
Step 8 |
adjustment-factor percentage Example: |
Configures TE to over-book (>100%) or under-book (<100%) the effective maximum reservable bandwidth (BMRe). The measured dark-bandwidth will be scaled based on the adjustment factor. Range is from 0 to 200. The default value is 100. |
||||
|
Step 9 |
flooding threshold up percentage down percentage Example: |
Configures the reserved bandwidth thresholds. When bandwidth crosses one of these thresholds, flooding is triggered. Range is from 0 to 100. The default value is 10. |
||||
|
Step 10 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
||||
|
Step 11 |
mpls traffic-eng link-management bandwidth-accounting enforce all Example: |
(Optional) Applies the measured rates immediately. When you apply measured rates immediately, the RSVP-TE bandwidth-accounting might flood the updated bandwidth values immediately. Applying measured rates immediately does not affect the periodic application of the bandwidth. |
||||
|
Step 12 |
clear mpls traffic-eng link-management bandwidth-accounting Example: |
(Optional) Erases the collected sample history and resets the application and sample timers. |
||||
|
Step 13 |
show interface type_path accounting Example: |
(Optional) Displays the per-interface SR accounting. |
||||
|
Step 14 |
show mpls traffic-eng link-management summary Example: |
(Optional) Displays a summary of link management information, including bandwidth accounting information. |
||||
|
Step 15 |
show mpls traffic-eng link-management advertisements Example: |
(Optional) Displays local link information that MPLS-TE link management is currently flooding into the global TE topology. |
||||
|
Step 16 |
show mpls traffic-eng link-management interfaces [ type interface-path-id ] [detail ] [ bandwidth-accounting ] Example: |
(Optional) Displays bandwidth accounting and utilization details and link management information. |
To display the per-interface SR counters, use the show interface type_path accounting command:
RP/0/RP0/CPU0:router# show interface hundredGigE 0/0/0/26 accounting
Mon Feb 3 23:29:48.449 UTC
HundredGigE0/0/0/26
Protocol Pkts In Chars In Pkts Out Chars Out
ARP 3 222 3 126
IPV6_ND 11 1122 13 1112
CLNS 99 121910 94 116212
SR_MPLS 0 0 3126 581436
Note |
The SR_MPLS counter is an egress-only counter and includes all traffic from the following:
|
To display detailed SR bandwidth utilization, use the show mpls traffic-eng link-management interface type_path detail command:
Router# show mpls traffic-eng link-management interface hundredGigE 0/0/0/26 detail bandwidth-accounting
System Information::
Links Count : 16 (Maximum Links Supported 800)
Link ID:: HundredGigE0/0/0/26 (26.1.1.1)
Local Intf ID: 22
Link Status:
Link Label Type : PSC
Physical BW : 1000000 kbits/sec
BCID : RDM
Max Reservable BW : 529309 kbits/sec (reserved: 94% in, 94% out)
Flooded Max Reservable BW: 529309 kbits/sec
BC0 (Res. Global BW) : 529309 kbits/sec (reserved: 94% in, 94% out)
BC1 (Res. Sub BW) : 0 kbits/sec (reserved: 100% in, 100% out)
MPLS TE Link State : MPLS TE on, RSVP on, admin-up
IGP Neighbor Count : 1
Max Res BW (RDM) : 900000 kbits/sec
BC0 (RDM) : 900000 kbits/sec
BC1 (RDM) : 0 kbits/sec
Max Res BW (MAM) : 0 kbits/sec
BC0 (MAM) : 0 kbits/sec
BC1 (MAM) : 0 kbits/sec
Bandwidth Accounting: Segment-Routing
Bandwidth Accounting Enforced: Yes
Bandwidth Utilization Details:
Sampling Interval : 30 sec
Application Interval : 90 sec
Adjustment Factor : 200%
Max Reservable BW Up Threshold : 30
Max Reservable BW Down Threshold: 30
Last Application at: 23:46:32 Mon 03 Feb 2020 (51 seconds ago)
Segment-Routing BW Utilization : 185346 kbits/sec
Adjusted BW Utilization : 370692 kbits/sec
Enforced BW Utilization : 370692 kbits/sec
Next Application at: 19:42:43 Sun 30 Apr 2017 (in 38 seconds)
Last Collection at : 19:41:42 Sun 30 Apr 2017 (23 seconds ago)
Next Collection at : 19:42:11 Sun 30 Apr 2017 (in 6 seconds)
Bandwidth Samples (Kbps):
Timestamp Segment-Routing
19:40:12 Sun 30 Apr 2017 187961
19:40:42 Sun 30 Apr 2017 180130
19:41:12 Sun 30 Apr 2017 187949
To display a summary of link management information, including bandwidth accounting information, use the show mpls traffic-eng link-management summary command:
Router# show mpls traffic-eng link-management summary
System Information::
Links Count : 14 (Maximum Links Supported 800)
Flooding System : enabled
IGP Areas Count : 1
IGP Areas
----------
IGP Area[1]:: IS-IS 0 level 2
Flooding Protocol : IS-IS
Flooding Status : flooded
Periodic Flooding : enabled (every 180 seconds)
Flooded Links : 7
IGP System ID : 0000.0000.0001
MPLS TE Router ID : 10.0.0.1
IGP Neighbors : 7
Bandwidth accounting:
Sampling interval: 30 seconds, Next in 29 seconds
Application interval: 90 seconds, Next in 1 secondsTo display local link information that MPLS-TE link management is currently flooding into the global TE topology, use the showmpls traffic-eng link-management advertisements command:
Router# show mpls traffic-eng link-management advertisements
Flooding Status : Ready
Last Flooding : 470 seconds ago
Last Flooding Trigger : Link BW changed
Next Periodic Flooding In : 143 seconds
Diff-Serv TE Mode : Not enabled
Configured Areas : 1
IGP Area[1]:: IS-IS 0 level 2
Flooding Protocol : IS-IS
IGP System ID : 0000.0000.0001
MPLS TE Router ID : 10.0.0.1
Flooded Links : 5
Link ID:: 0 (GigabitEthernet0/1/1/0)
Link IP Address : 10.12.110.1
O/G Intf ID : 22
Neighbor : ID 0000.0000.0002.00, IP 10.12.110.2
TE Metric : 10
IGP Metric : 10
Physical BW : 1000000 kbits/sec
BCID : RDM
Max Reservable BW : 899999 kbits/sec
Res Global BW : 899999 kbits/sec
Res Sub BW : 0 kbits/sec
|
Feature Name |
Release Information |
Feature Description |
|---|---|---|
|
Configure Autoroute Tunnel as Designated Path |
Release 7.6.2 |
Simplify the path selection for a traffic class and split traffic among multiple TE tunnels to achieve many benefits such as security and service-level agreements. You can now exclusively specify an autoroute tunnel to forward traffic to a particular tunnel destination address without considering the IS-IS metric for traffic path selection. Earlier, MPLS-TE considered either the Forwarding Adjacency (FA) or Autoroute (AA) tunnel to forward traffic based only on IS-IS metric. The feature introduces the mpls traffic-eng tunnel restricted command. |
MPLS-TE builds a unidirectional tunnel from a source to a destination using label switched path (LSP) to forward traffic.
To forward the traffic through MPLS tunneling, you can use autoroute, forwarding adjacency, or static routing:
Autoroute (AA) functionality allows to insert the MPLS TE tunnel in the Shortest Path First (SPF) tree for the tunnel to transport all the traffic from the headend to all destinations behind the tail-end. AA is only known to the tunnel headend router.
Forwarding Adjacency (FA) allows the MPLS-TE tunnel to be advertised as a link in an IGP network with the cost of the link associated with it. Routers outside of the TE domain can see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.
Static routing allows you to inject static IP traffic into a tunnel as the output interface for the routing decision.
Prior to this release, by default, MPLS-TE considers FA or AA tunnels to forward traffic based on the IS-IS metric. The lower metric is always used to forward traffic. There was no mechanism to forward traffic to a specific tunnel interface.
For certain prefixes to achieve many benefits such as security and service-level agreements, there might be a need to forward traffic to a specific tunnel interface that has a matching destination address.
With this feature, you can exclusively use AA tunnels to forward traffic to their tunnel destination address irrespective of IS-IS metric. Traffic steering is performed based on the prefixes and not metrics. Traffic to other prefixes defaults to the forwarding-adjacency (FA) tunnels.
To enable this feature, use the mpls traffic-eng tunnel restricted command.
Also, you may require more than one AA tunnel to a particular remote PE and use ECMP to forward traffic across AA tunnels. You can configure a loopback interface with one primary address and multiple secondary addresses on the remote PE, using one IP for the FA tunnel destination, and others for the AA tunnels destinations. Multiple IP addresses are advertised in the MPLS TE domain using the typed length value (TLV) 132 in IS-IS. A TLV-encoded data stream contains code related to the record type, the record length of the value, and value. TLV 132 represents the IP addresses of the transmitting interface.
When MPLS-TE tunnel restricted is configured, the following is the behavior:
A complete set of candidate paths is available for selection on a per-prefix basis during RIB update as the first hop computation includes all the AA tunnels terminating on a node up to a limit of 64 and the lowest cost forwarding-adjacency or native paths terminating on the node or inherited from the parent nodes in the first hops set for the node.
During per-prefix computation, AA tunnel first hops are used for traffic sent to their tunnel destination address even if FA tunnel or native first hops have a better metric. AA tunnel first-hops are not used for any other prefixes.
ECMP is used when multiple AA tunnel first hops have the same destination address and metric.
During per-prefix computation, AA tunnel first hops are used for traffic sent to their tunnel destination address, and for all other destinations on the tunnel tail node or behind it, even if a native path has a better metric.
Adding mpls traffic-eng tunnel preferred configuration has no effect when the tunnel restricted is already configured.
If there’s no AA tunnel or if the tunnel is down, then native paths are used for all other destinations on the tunnel tail node or behind it.
The route metric for a prefix reflects the chosen first-hop, not necessarily the lowest cost SPF distance to the node.
The total number of interface addresses to the number that can be contained in 255 bytes is 63 for IPv4 and 15 for IPv6.
When this feature is enabled, a maximum of 64 tunnels can terminate on the tail node.
Let's understand how to configure the feature using the following topology:
Consider the topology where PE1 has three MPLS tunnels connecting to PE2.
Tunnel-t31: Forwarding adjacency (FA) is configured to the primary address of Loopback 0 on PE2 (10.1.1.103).
Tunnel- t32: Autoroute announce (AA) is configured to a secondary address of Loopback 0 on PE2 (10.1.2.103).
Tunnel-t33: Autoroute announce (AA) is configured to a secondary address of Loopback 0 on PE2 (10.1.3.103).
This feature is not enabled by default. When this feature is not enabled, traffic is load balanced over all AA tunnels towards the same remote PE provided the tunnel metric is the same:
Router# show routes
i L2 10.1.1.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
i L2 10.1.2.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
i L2 10.1.3.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
i L2 10.2.0.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
10.2.0.104/32 [115/50] via 10.1.2.103, 00:00:30, tunnel-t32
[115/50] via 10.1.3.103, 00:00:30, tunnel-t33
You can configure the feature using the mpls traffic-eng tunnel restricted command.
RP/0/RSP0/CPU0:ios# configure
RP/0/RSP0/CPU0:ios(config)# router isis 1
RP/0/RSP0/CPU0:ios(config-isis)# address-family ipv4 unicast
RP/0/RSP0/CPU0:ios(config-isis-af# mpls traffic-eng tunnel restricted
The following example shows the AA tunnel metric running configuration:
router isis 1
address-family ipv4 unicast
mpls traffic-eng tunnel restricted
!
!
end
When you enable the feature, traffic towards a particular prefix is sent only over the tunnel that has that IP address as destination.
Router# show route
i L2 10.1.1.103/32 [115/40] via 10.1.1.103, 00:00:04, tunnel-t31
i L2 10.1.2.103/32 [115/40] via 10.1.2.103, 00:00:04, tunnel-t32
i L2 10.1.3.103/32 [115/40] via 10.1.3.103, 00:00:04, tunnel-t33
i L2 10.2.0.103/32 [115/40] via 10.1.1.103, 00:00:04, tunnel-t31
i L2 10.2.0.104/32 [115/50] via 10.1.1.103, 00:00:04, tunnel-t31
When multiple restricted AA tunnels are created towards the same destination IP address, router load balances traffic across all those tunnels:
Router# show route
i L2 10.1.1.103/32 [115/40] via 10.1.1.101, 00:00:08, GigabitEthernet0/0/0/2
[115/40] via 10.1.3.101, 00:00:08, GigabitEthernet0/0/0/3
i L2 10.1.2.103/32 [115/40] via 10.1.2.103, 00:00:08, tunnel-t32
[115/40] via 10.1.2.103, 00:00:30, tunnel-t34
i L2 10.1.3.103/32 [115/40] via 10.1.3.103, 00:00:08, tunnel-t33
i L2 10.2.0.103/32 [115/40] via 10.1.1.101, 00:00:08, GigabitEthernet0/0/0/2
[115/40] via 10.1.3.101, 00:00:08, GigabitEthernet0/0/0/3
i L2 10.2.0.104/32 [115/50] via 10.1.1.101, 00:00:08, GigabitEthernet0/0/0/2
[115/50] via 10.1.3.101, 00:00:08, GigabitEthernet0/0/0/3
Fast Reroute (FRR) is a mechanism for protecting MPLS TE LSPs from link and node failures by locally repairing the LSPs at the point of failure, allowing data to continue to flow on them while their headend routers try to establish new end-to-end LSPs to replace them. FRR locally repairs the protected LSPs by rerouting them over backup tunnels that bypass failed links or node.
Note |
If FRR is greater than 50ms, it might lead to a loss of traffic. |
Backup tunnels that bypass only a single link of the LSP’s path provide link protection. They protect LSPs if a link along their path fails by rerouting the LSP’s traffic to the next hop (bypassing the failed link). These tunnels are referred to as next-hop (NHOP) backup tunnels because they terminate at the LSP’s next hop beyond the point of failure.
FRR provides node protection for LSPs. Backup tunnels that bypass next-hop nodes along LSP paths are called next-next-hop (NNHOP) backup tunnels because they terminate at the node following the next-hop node of the LSP paths, bypassing the next-hop node. They protect LSPs if a node along their path fails by enabling the node upstream of the failure to reroute the LSPs and their traffic around the failed node to the next-next hop. NNHOP backup tunnels also provide protection from link failures, because they bypass the failed link and the node.
MPLS Differentiated Services Aware Traffic Engineering (DS-TE) is an extension of the regular MPLS-TE feature. Regular traffic engineering does not provide bandwidth guarantees to different traffic classes. A single bandwidth constraint is used in regular TE that is shared by all traffic. To support various classes of service (CoS), you can configure multiple bandwidth constraints. These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint.
Cisco IOS XR software supports two DS-TE modes: pre-standard and IETF. The pre-standard DS-TE mode uses the Cisco proprietary mechanisms for RSVP signaling and IGP advertisements. This DS-TE mode does not interoperate with third-party vendor equipment. Pre-standard DS-TE is enabled only after configuring the sub-pool bandwidth values on MPLS-enabled interfaces. Pre-standard DS-TE mode supports a single bandwidth constraint model a Russian Doll Model (RDM) with two bandwidth pools: global-pool and sub-pool. TE class map is not used with Pre-standard DS-TE mode.
IETF DS-TE mode uses IETF-defined extensions for RSVP and IGP. This mode inter-operates with third-party vendor equipment. IETF mode supports multiple bandwidth constraint models, including RDM and Maximum Allocation Bandwidth Constraint Model (MAM), both with two bandwidth pools. In an IETF DS-TE network, identical bandwidth constraint models must be configured on all nodes. TE class map is used with IETF DS-TE mode and must be configured the same way on all nodes in the network.
The MAM constraint model has the following characteristics:
Easy to use and intuitive.
Isolation across class types.
Simultaneously achieves isolation, bandwidth efficiency, and protection against QoS degradation.
The RDM constraint model has these characteristics:
Allows greater sharing of bandwidth among different class types.
Ensures bandwidth efficiency simultaneously and protection against QoS degradation of all class types.
Specifies that it is used with preemption to simultaneously achieve isolation across class-types such that each class-type is guaranteed its share of bandwidth, bandwidth efficiency, and protection against QoS degradation of all class types.
MPLS TE forwarding adjacency allows you to handle a TE label-switched path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network that is based on the Shortest Path First (SPF) algorithm. Both Intermediate System-to-Intermediate System (IS-IS) and Open Shortest Path First (OSPF) are supported as the IGP. A forwarding adjacency can be created between routers regardless of their location in the network. The routers can be located multiple hops from each other.
As a result, a TE tunnel is advertised as a link in an IGP network with the tunnel's cost associated with it. Routers outside of the TE domain see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network. TE tunnel interfaces are advertised in the IGP network just like any other links. Routers can then use these advertisements in their IGPs to compute the SPF even if they are not the headend of any TE tunnels.
Automatic bandwidth allows you to dynamically adjust bandwidth reservation based on measured traffic. MPLS-TE automatic bandwidth is configured on individual Label Switched Paths (LSPs) at every headend router. MPLS-TE automatic bandwidth monitors the traffic rate on a tunnel interface and resizes the bandwidth on the tunnel interface to align it closely with the traffic in the tunnel.
For every traffic-engineered tunnel that is configured for an automatic bandwidth, the average output rate is sampled, based on various configurable parameters. Then, the tunnel bandwidth is readjusted automatically based on either the largest average output rate that was noticed during a certain interval, or a configured maximum bandwidth value.
While re-optimizing the LSP with the new bandwidth, a new path request is generated. If the new bandwidth is not available, the last good LSP remains used. This way, the network experiences no traffic interruptions. If minimum or maximum bandwidth values are configured for a tunnel, the bandwidth, which the automatic bandwidth signals, stays within these values.
The output rate on a tunnel is collected at regular intervals that are configured by using the application command in MPLS-TE auto bandwidth interface configuration mode. When the application period timer expires, and when the difference between the measured and the current bandwidth exceeds the adjustment threshold, the tunnel is re-optimized. Then, the bandwidth samples are cleared to record the new largest output rate at the next interval. If a tunnel is shut down, and is later brought again, the adjusted bandwidth is lost, and the tunnel is brought back with the initially configured bandwidth. When the tunnel is brought back, the application period is reset.
The MPLS-TE interarea tunneling feature allows you to establish TE tunnels spanning multiple Interior Gateway Protocol (IGP) areas and levels, thus eliminating the requirement that headend and tailend routers reside in a single area.
Interarea support allows the configuration of a TE LSP that spans multiple areas, where its headend and tailend label switched routers (LSRs) reside in different IGP areas. Customers running multiple IGP area backbones (primarily for scalability reasons) requires Multiarea and Interarea TE . This lets you limit the amount of flooded information, reduces the SPF duration, and lessens the impact of a link or node failure within an area, particularly with large WAN backbones split in multiple areas.
The following figure shows a typical interarea TE network using OSPF.
The following figure shows a typical interlevel (IS-IS) TE Network.
As shown in the topology, R2, R3, R7, and R4 maintain two databases for routing and TE information. For example, R3 has TE topology information related to R2, flooded through Level-1 IS-IS LSPs plus the TE topology information related to R4, R9, and R7, flooded as Level 2 IS-IS Link State PDUs (LSPs) (plus, its own IS-IS LSP).
Loose hop optimization allows the re-optimization of tunnels spanning multiple areas and solves the problem which occurs when an MPLS-TE LSP traverses hops that are not in the LSP's headend's OSPF area and IS-IS level. Interarea MPLS-TE allows you to configure an interarea traffic engineering (TE) label switched path (LSP) by specifying a loose source route of ABRs along the path. Then it is the responsibility of the ABR (having a complete view of both areas) to find a path obeying the TE LSP constraints within the next area to reach the next hop ABR (as specified on the headend router). The same operation is performed by the last ABR connected to the tailend area to reach the tailend LSR.
Network performance metrics such as packet loss, delay, delay variation, and bandwidth utilization is a critical measure for traffic engineering (TE) in service provider networks. These network performance metrics provide network operators information about the performance characteristics of their networks for performance evaluation and helps to ensure compliance with service level agreements. The service-level agreements (SLAs) of service providers depend on the ability to measure and monitor these network performance metrics. Network operators can use performance measurement (PM) feature to monitor the network metrics for links as well as end-to-end TE label switched paths (LSPs).
To configure the metric type to be used for path calculation for a given tunnel, use the path-selection metric command in either the MPLS-TE configuration mode or under the tunnel interface configuration mode.
The metric type specified per interface takes the highest priority, followed by the MPLS-TE global metric type.
Note |
If the delay metric is configured, CSPF finds a path with optimizedminimum link delay metric. See the Configuring Performance Measurement chapter in the Segment Routing Configuration Guide for information on configuring interface performance delay measurement. |
Configuration Example
The following example shows how to set the path-selection metric to use the IGP metric under a specific tunnel interface:
Router# configure
Router(config)# interface tunnel-te 1
Router(config-if)# path-selection metric igp
Router(config-if)# commitThe following example shows how to set the path-selection metric to use the delay metric under the MPLS-TE configuration mode:
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# path-selection metric delay
Router(config-mpls-te)# commit Apply the path-selection delay-limit configuration to set the upper limit on the path aggregate delay when computing paths for MPLS-TE LSPs. After you configure the path-selection delay-limit value, if the sum of minimum-delay metric from all links that are traversed by the path exceeds the specified delay-limit, CSPF will not return any path. The periodic path verification checks if the delay-limit is crossed.
The path-selection delay-limit value can be configured at the global MPLS-TE, per-interface tunnel, and per path-option attribute set. The path-selection delay-limit per path-option attribute set takes the highest priority, followed by per-interface, and then the MPLS-TE global path-selection delay-limit values.
The delay limit range is a value from 1 to 4294967295 microseconds.
Note |
See the Configuring Performance Measurement chapter in the Segment Routing Configuration Guide for information on configuring interface performance delay measurement. |
Configuration Example
The following example shows how to set the path-selection delay limit under a specific tunnel interface:
Router# configure
Router(config)# interface tunnel-te2000
Router(config-if)# path-selection metric delay
Router(config-if)# path-selection delay-limit 200
Router(config-if)# commitThe following example shows how to set the path-selection delay limit under a path-option attribute set:
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# attribute-set path-option test
Router(config-te-attribute-set)# path-selection delay-limit 300
Router(config-te-attribute-set)# root
Router(config)# interface tunnel-te1000
Router(config-if)# path-option 10 dynamic attribute-set test
Router(config-if)# commitThe following example shows how to set the path-selection delay limit under the global MPLS-TE configuration mode:
Router# configure
Router(config)# mpls traffic-eng
Router(config-mpls-te)# path-selection metric delay
Router(config-mpls-te)# path-selection delay-limit 150
Router(config-mpls-te)# commitFor additional information related to implementing MPLS-TE, refer to the following references:
|
Related Topic |
Document Title |
|---|---|
|
MPLS-TE commands |
MPLS Traffic Engineering Commands module in MPLS Command Reference for Cisco 8000 Series Routers. |
|
Standards |
Title |
|---|---|
|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
— |
|
MIBs |
MIBs Link |
|---|---|
| — |
To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http://cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml |
|
RFCs |
Title |
|---|---|
|
RFC 4124 |
Protocol Extensions for Support of Diffserv-aware MPLS Traffic Engineering, F. Le Faucheur, Ed. June 2005. (Format: TXT=79265 bytes) (Status: PROPOSED STANDARD) |
|
RFC 4125 |
Maximum Allocation Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering, F. Le Faucheur, W. Lai. June 2005. (Format: TXT=22585 bytes) (Status: EXPERIMENTAL) |
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RFC 4127 |
Russian Dolls Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering, F. Le Faucheur, Ed. June 2005. (Format: TXT=23694 bytes) (Status: EXPERIMENTAL) |
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Description |
Link |
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