MPLS Traffic Engineering Interarea Tunnels
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MPLS Traffic Engineering Interarea TunnelsLast Updated: March 1, 2012
The MPLS Traffic Engineering: Interarea Tunnels feature allows you to establish Multiprotocol Label Switching (MPLS) traffic engineering (TE) tunnels that span multiple Interior Gateway Protocol (IGP) areas and levels, removing the restriction that had required the tunnel headend and tailend routers both be in the same area. The IGP can be either Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF).
Finding Feature InformationYour software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required. Prerequisites for MPLS Traffic Engineering Interarea TunnelsRestrictions for MPLS Traffic Engineering Interarea Tunnels
Information About MPLS Traffic Engineering Interarea Tunnels
Interarea Tunnels FunctionalityTo configure an interarea tunnel, you specify on the headend router a loosely routed explicit path for the tunnel label switched path (LSP) that identifies each 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. For example, to configure a TE tunnel from router R1 to router R3 in the simple multiarea network shown in the figure below, you would specify ABR1 and ABR2 as loose hops in the explicit path for the tunnel.
To signal the tunnel LSP, the headend router (R1) computes the path to ABR1 and sends a Resource Reservation Protocol (RSVP) Path message specifying the path from itself to ABR1 as a sequence of strict hops followed by the path from ABR1 to the tailend as a sequence of loose hops (ABR2, R3). When ABR1 receives the Path message, it expands the path across the backbone area to ABR2 and forwards the Path message specifying the path from itself to ABR2 as a sequence of strict hops followed by the path from ABR2 to the tunnel tailend (R3) as a loose hop. When ABR2 receives the Path message, it expands the path across the tailend area to R3 and propagates the Path message specifying the path from itself to R2 as a sequence of strict hops.
The following MPLS TE features are supported on interarea traffic engineering LSPs: Autoroute Destination FunctionalityThe autoroute destination feature allows you to automatically route traffic through a TE tunnel instead of manually configuring static routes. You enable this feature on a per-tunnel basis by using the tunnel mpls traffic-eng autoroute destination command. The following sections describe how the autoroute destination feature interacts with other features:
CBTS Interaction with Autoroute DestinationTE tunnels that have the autoroute destination feature enabled can also be configured as class-based traffic shaping (CBTS) tunnel bundle masters or members. Within a CBTS bundle, only the master tunnel with autoroute destination enabled is installed into the Routing Information Base (RIB); that is, the member tunnels are not installed into the RIB. If member tunnels that have autoroute destination enabled are unconfigured from the bundle, they become regular TE tunnels and TE requests that the static process installs static routes over those tunnels in the RIB. Conversely, when regular TE tunnels with autoroute destination enabled are added to a CBTS bundle as members, TE requests that the static process removes the automatic static routes over those tunnels from the RIB. Manually Configured Static Routes Interaction with Autoroute DestinationIf there is a manually configured static route to the same destination as a tunnel with autoroute destination enabled via the tunnel mpls traffic-eng autoroute destination command, traffic for that destination is load-shared between the static route and the tunnel with autoroute destination enabled. Autoroute Announce Interaction with Autoroute DestinationFor intra-area tunnels, if a tunnel is configured with both autoroute announce and autoroute destination, the tunnel is announced to the RIB by both the IGP and the static process. RIBs prefer static routes, not IGP routes, so the autoroute destination features takes precedence over autoroute announce. Forwarding Adjacency Interaction with Autoroute DestinationIf a tunnel is configured with both forwarding adjacency and autoroute destination, the tunnel is announced to the RIB by both the IGP and the static process. The RIB prefers the static route. However, because the IGP was notified about the tunnel via the forwarding adjacency command and the tunnel information was flooded, forwarding adjacency continues to function. MPLS Traffic Engineering Interarea Tunnels Benefits
How to Configure MPLS Traffic Engineering Interarea Tunnels
Configuring OSPF for Interarea TunnelsConfiguring OSPF for ABR RoutersFor each ABR that is running OSPF, perform the following steps to configure traffic engineering on each area you want tunnels in or across. By having multiple areas and configuring traffic engineering in and across each area, the router can contain changes within the network within an area. DETAILED STEPS Configuring OSPF for Non-ABR RoutersFor each non-ABR that is running OSPF, perform the following steps to configure OSPF.
DETAILED STEPS
Configuring IS-IS for Interarea Tunnels
Configuring IS-IS for Backbone RoutersTo configure IS-IS for background (level-1-2) routers, perform the following steps.
DETAILED STEPS
Configuring IS-IS for Nonbackbone RoutersTo configure IS-IS for nonbackbone routers, perform the following steps.
DETAILED STEPS
Configuring IS-IS for InterfacesTo configure IS-IS for interfaces, perform the following steps.
DETAILED STEPS
Configuring MPLS and RSVP to Support Traffic EngineeringSUMMARY STEPS
DETAILED STEPS
Configuring an MPLS Traffic Engineering Interarea Tunnel
Configuring an MPLS Traffic Engineering Interarea Tunnel to Use Explicit PathsSUMMARY STEPS
DETAILED STEPS
Configuring Explicit PathsSUMMARY STEPS
DETAILED STEPS
Configuring an MPLS Traffic Engineering Tunnel with Autoroute DestinationSUMMARY STEPS
DETAILED STEPS
Configuration Examples for MPLS Traffic Engineering Interarea Tunnels
Configuring OSPF for Interarea Tunnels ExampleThe following configuration fragments show how to configure OSPF for interarea tunnels assuming that: Router R1 OSPF Configurationrouter ospf 1 network 192.168.10.10 0.0.0.0 area 1 network 192.168.35.0 0.0.0.255 area 1 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 1 Router Rx OSPF Configurationrouter ospf 1 network 192.168.30.30 0.0.0.0 area 1 network 192.168.35.0 0.0.0.255 area 1 network 192.168.45.0 0.0.0.255 area 1 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 1 Router Ra OSPF ConfigurationRa is an ABR for Area 0 and Area 1. Interface POS2/0 is in Area 1 and interface POS3/0 is in Area 0. The mpls traffic-eng area commands configure Ra for IGP TE updates for both areas. router ospf 1 network 192.168.40.40 0.0.0.0 area 0 network 192.168.45.0 0.0.0.255 area 1 network 192.168.55.0 0.0.0.255 area 0 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 0 mpls traffic-eng area 1 Router Rb OSPF ConfigurationRb is an ABR for Area 0 and Area 2. Interface POS4/0 is in Area 0 and interface POS5/0 is in Area 2. The mpls traffic-eng area commands configure Rb for IGP TE updates for both areas. router ospf 1 network 192.168.60.60 0.0.0.0 area 0 network 192.168.65.0 0.0.0.255 area 0 network 192.168.75.0 0.0.0.255 area 2 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 0 mpls traffic-eng area 2 Router Rz OSPF Configuration router ospf 1 network 192.168.70.70 0.0.0.0 area 2 network 192.168.75.0 0.0.0.255 area 2 network 192.168.85.0 0.0.0.255 area 2 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 2 Router R2 OSPF Configuration router ospf 1 network 192.168.20.20 0.0.0.0 area 2 network 192.168.85.0 0.0.0.255 area 2 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 2 Configuring IS-IS for Interarea Tunnels ExampleThe following configuration fragments illustrate how to configure IS-IS for interarea tunnels assuming that: Router R1 IS-IS Configurationinterface POS1/0 ip router isis router isis metric-style wide net 10.0000.0100.0000.0010 mpls traffic-eng router-id Loopback0 mpls traffic-eng level-1 Router Rx IS-IS Configurationclns routing interface POS1/0 ip router isis interface POS2/0 ip router isis router isis metric-style wide net 10.0000.2000.0100.0001 mpls traffic-eng router-id Loopback0 mpls traffic-eng level-1 Router Ra IS-IS Configurationclns routing interface POS2/0 ip router isis interface POS3/0 ip router isis router isis metric-style wide net 10.0000.2000.0200.0002 mpls traffic-eng router-id Loopback0 mpls traffic-eng level-1 mpls traffic-eng level-2 Router Ry IS-IS Configurationclns routing interface POS3/0 ip router isis interface POS4/0 ip router isis router isis metric-style wide net 10.0000.2000.0300.0003 mpls traffic-eng router-id Loopback0 mpls traffic-eng level-2 Router Rb IS-IS Configurationclns routing interface POS4/0 ip router isis interface POS5/0 ip router isis router isis metric-style wide net 10.0000.2000.0400.0004 mpls traffic-eng router-id Loopback0 mpls traffic-eng level-1 mpls traffic-eng level-2 Configuring MPLS and RSVP to Support Traffic Engineering ExampleThe following configuration fragments show how to configure MPLS and RSVP to support traffic engineering on the routers. Router R1 Traffic Engineering Configurationip cef mpls traffic-eng tunnels interface Loopback0 ip address 192.168.10.10 255.255.255.255 interface POS1/0 !Each interface supporting MPLS TE must include the following: mpls traffic-eng tunnels ip rsvp bandwidth The configuration of routers Rx, Ra, Ry, Rb, Rz, and R2 for traffic engineering operation is similar to that for R1. Configuring an MPLS Traffic Engineering Interarea Tunnel ExampleThe following configuration fragments show how to configure an MPLS traffic engineering interarea tunnel. Tunnel1 is configured with a path option that is loosely routed through Ra and Rb. R1 Interarea Tunnel ConfigurationThe following commands configure an MPLS TE tunnel to use explicit paths: interface Tunnel1 ip unnumbered Loopback0 tunnel destination 192.168.20.20 tunnel mode mpls traffic-eng tunnel mpls traffic-eng bandwidth 300 tunnel mpls traffic-eng path-option 1 explicit name path-tunnel1 The following commands configure an explicit path: ip explicit-path name path-tunnel1 next-address loose 192.168.40.40 next-address loose 192.168.60.60 next-address loose 192.168.20.20 !Specifying the tunnel tailend in the loosely routed !path is optional.
Additional ReferencesRelated DocumentsMIBsTechnical Assistance
Feature Information for MPLS Traffic Engineering Interarea TunnelsThe following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
GlossaryABR --Area Border Router.A router connecting two areas. In OSPF, ABRs belong to both areas and must maintain separate topological databases for each. When an OSPF router has interfaces in more than one area, it is an Area Border Router. area --A logical set of network segments (for example, one that is OSPF-based) and their attached devices. Areas usually are connected to other areas by routers, making up a single autonomous system. OSPF and IS-IS define their areas differently. OSPF area borders are marked by routers. Some interfaces are in one area, and other interfaces are in another area. With IS-IS, all the routers are completely within an area, and the area borders are on links, not on routers. The routers that connect the areas are level-2 routers, and routers that have no direct connectivity to another area are level-1 routers. area ID --In an IS-IS router, this area address is associated with the entire router rather than an interface. A router can have up to three area addresses. Both the area ID and the system ID are defined on an IS-IS router by a single address, the Network Entry Title (NET). autonomous system --A collection of networks under a common administration sharing a common routing strategy. Autonomous systems are subdivided by areas. Cisco Express Forwarding --An advanced Layer 3 IP switching technology. Cisco Express Forwarding optimizes network performance and scalability for networks that have large and dynamic traffic patterns, such as the Internet, and for networks characterized by intensive Web-based applications or interactive sessions. Cisco Express Forwarding uses a Forwarding Information Base (FIB) to make IP destination prefix-based switching decisions. The FIB is conceptually similar to a routing table or information base. When routing or topology changes occur in the network, the IP routing table is updated, and those changes are reflected in the FIB. The FIB maintains next-hop address information based on the information in the IP routing table. headend --The upstream, transmit end of a tunnel. The router that originates and maintains the traffic engineering LSP. IGP --Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common IGPs include OSPF and Routing Information Protocol (RIP). interarea TE --Ability for a traffic engineering LSP to span multiple areas. IS-IS --Intermediate System-to-Intermediate System. IS-IS is an OSI link-state hierarchical routing protocol based on DECnet Phase V routing, where intermediate system (IS) routers exchange routing information based on a single metric to determine the network topology. label switched path (LSP) tunnel --A configured connection between two routers in which label switching is used to carry the packets. level-1 routers --Routers that are directly connected to other areas. The routers are not in the backbone. MPLS does not run in the background. These routers are also called internal routers. level-2 routers --Routers that connect two areas. These routers let you run MPLS in the background. load balancing --The distribution of traffic among multiple paths to the same destination so that the router uses bandwidth efficiently. Load balancing increases the use of network segments, thus increasing effective network bandwidth. LSP --label switched path. A sequence of hops such as R0...Rn in which a packet travels from R0 to Rn through label switching mechanisms. A label switched path can be chosen dynamically, based on normal routing mechanisms, or through configuration. mask --A bit combination used to describe which part of an address refers to the network or the subnet and which part refers to the host. MPLS --Multiprotocol Label Switching. A method for forwarding packets (frames) through a network. It enables routers at the edge of a network to apply labels to packets. ATM switches or existing routers in the network core can switch packets according to the labels with minimal lookup overhead. OSPF --Open Shortest Path First. Link-state, hierarchical IGP routing algorithm proposed as a successor to Routing Information Protocol (RIP) in the Internet community. OSPF features include least-cost routing, multipath routing, and load balancing. process ID --Distinguishes one process from another within the device. An OSPF process ID can be any positive integer, and it has no significance outside the router on which it is configured. router ID --Something by which a router originating a packet can be uniquely distinguished from all other routers. For example, an IP address from one of the router's interfaces. static routing --A static route is a fixed path preprogrammed by a network administrator. Static routes cannot make use of routing protocols and don't self-update after receipt of routing update messages; they must be updated by hand. tailend --The downstream, receive end of a tunnel. The router that terminates the traffic engineering LSP. traffic engineering --The techniques and processes that cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods were used. tunnel --A secure communication path between two peers, such as two routers. A traffic engineering tunnel is a label switched tunnel that is used for traffic engineering. Such a tunnel is set up through means other than normal Layer 3 routing; it is used to direct traffic over a path different from the one that Layer 3 routing could cause the tunnel to take. virtual link --Ordinarily, each area is directly connected to area 0. A virtual link is used for a connection when an area is connected to an area that is one area away from area 0. Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R) Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. © 2012 Cisco Systems, Inc. All rights reserved.
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