- Read Me First
- MPLS LDP Graceful Restart
- NSF SSO--MPLS LDP and LDP Graceful Restart
- ISSU MPLS Clients
- MPLS Traffic Engineering--RSVP Graceful Restart
- NSF SSO--MPLS TE and RSVP Graceful Restart
- AToM Graceful Restart
- NSF SSO--Any Transport over MPLS and AToM Graceful Restart
- Configuring NSF SSO--MPLS VPN
- SSO and ISSU--MPLS VPN 6VPE and 6PE Support
- SSO Support for MPLS TE Autotunnel and Automesh
- MPLS Traffic Engineering Nonstop Routing Support
Contents
- MPLS LDP Graceful Restart
- Finding Feature Information
- Prerequisites for MPLS LDP Graceful Restart
- Restrictions for MPLS LDP Graceful Restart
- Information About MPLS LDP Graceful Restart
- How MPLS LDP Graceful Restart Works
- How a Route Processor Advertises That It Supports MPLS LDP Graceful Restart
- What Happens If a Route Processor Does Not Have MPLS LDP Graceful Restart
- How to Configure MPLS LDP Graceful Restart
- Configuring MPLS LDP Graceful Restart
- Verifying the MPLS LDP Graceful Restart Configuration
- Configuration Examples for MPLS LDP Graceful Restart
- Configuring MPLS LDP Graceful Restart Example
- Additional References
- Feature Information for MPLS LDP Graceful Restart
MPLS LDP Graceful Restart
When a router is configured with Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) Graceful Restart (GR), it assists a neighboring router that has MPLS LDP Stateful Switchover/Nonstop Forwarding (SSO/NSF) Support and Graceful Restart to recover gracefully from an interruption in service. MPLS LDP GR functions strictly in helper mode, which means it can only help other routers that are enabled with MPLS SSO/NSF and GR to recover. If the router with LDP GR fails, its peer routers cannot help the router recover.
For brevity, the following are used in this document:
MPLS LDP SSO/NSF Support and Graceful Restart is called LDP SSO/NSF.
The MPLS LDP GR feature described in this document refers to helper mode.
When you enable MPLS LDP GR on a router that peers with an MPLS LDP SSO/NSF-enabled router, the SSO/NSF-enabled router can maintain its forwarding state when the LDP session between them is interrupted. While the SSO/NSF-enabled router recovers, the peer router forwards packets using stale information. This enables the SSO/NSF-enabled router to become operational more quickly.
- Finding Feature Information
- Prerequisites for MPLS LDP Graceful Restart
- Restrictions for MPLS LDP Graceful Restart
- Information About MPLS LDP Graceful Restart
- How to Configure MPLS LDP Graceful Restart
- Configuration Examples for MPLS LDP Graceful Restart
- Additional References
- Feature Information for MPLS LDP Graceful Restart
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 module.
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 LDP Graceful Restart
You must enable MPLS LDP GR on all route processors for an LDP session to be preserved during an interruption in service.
Restrictions for MPLS LDP Graceful Restart
Information About MPLS LDP Graceful Restart
- How MPLS LDP Graceful Restart Works
- How a Route Processor Advertises That It Supports MPLS LDP Graceful Restart
- What Happens If a Route Processor Does Not Have MPLS LDP Graceful Restart
How MPLS LDP Graceful Restart Works
MPLS LDP GR works in strict helper mode, which means it helps a neighboring route processor that has MPLS LDP SSO/NSF to recover from disruption in service without losing its MPLS forwarding state. The disruption in service could be the result of a TCP or UDP event or the stateful switchover of a route processor. When the neighboring router establishes a new session, the LDP bindings and MPLS forwarding states are recovered.
In the topology shown in the figure below, the following elements have been configured:
LDP sessions are established between Router 1 and Router 2, as well as between Router 2 and Router 3.
Router 2 has been configured with MPLS LDP SSO/NSF. Routers 1 and 3 have been configured with MPLS LDP GR.
A label switched path (LSP) has been established between Router 1 and Router 3.
The following process shows how Routers 1 and 3, which have been configured with MPLS LDP GR, help Router 2, which has been configured with LDP SSO/NSF, recover from a disruption in service:
Router 1 notices an interruption in service with Router 2. (Router 3 also performs the same actions in this process.)
Router 1 marks all the label bindings from Router 2 as stale, but it continues to use the bindings for MPLS forwarding.
Router 1 reestablishes an LDP session with Router 2, but keeps its stale label bindings. If you issue a showmplsldpneighbor command with the graceful-restart keyword, the command output displays the recovering LDP sessions.
Both routers readvertise their label binding information. If Router 1 relearns a label from Router 2 after the session has been established, the stale flags are removed. The showmplsforwarding-tablecommand displays the information in the MPLS forwarding table, including the local label, outgoing label or VC, prefix, label-switched bytes, outgoing interface, and next hop.
You can set various graceful restart timers. See the following commands for more information:
How a Route Processor Advertises That It Supports MPLS LDP Graceful Restart
A Route Processor (RP) that is configured to perform MPLS LDP GR includes the Fault Tolerant (FT) Type Length Value (TLV) in the LDP initialization message. The RP sends the LDP initialization message to a neighbor to establish an LDP session.
The FT session TLV includes the following information:
The Learn from Network (L) flag is set to 1, which indicates that the route processor is configured to perform MPLS LDP GR.
The Reconnect Timeout field shows the time (in milliseconds) that the neighbor should wait for a reconnection if the LDP session is lost. In this release, the timer is set to 0, which indicates that if the local router fails, its peers should not wait for it to recover. The timer setting indicates that the local router is working in helper mode.
The Recovery Time field shows the time (in milliseconds) that the neighbor should retain the MPLS forwarding state during a recovery. If a neighbor did not preserve the MPLS forwarding state before the restart of the control plane, the neighbor sets the recovery time to 0.
What Happens If a Route Processor Does Not Have MPLS LDP Graceful Restart
If two route processors establish an LDP session and one route processor is not configured for MPLS LDP GR, the two route processors create a normal LDP session but do not have the ability to perform MPLS LDP GR. Both route processors must be configured for MPLS LDP GR.
How to Configure MPLS LDP Graceful Restart
Configuring MPLS LDP Graceful Restart
To configure MPLS LDP Graceful Restart, perform the following task.
You must enable MPLS LDP GR on all route processors for an LDP session to be preserved during an interruption in service.
MPLS LDP GR is enabled globally. When you enable MPLS LDP GR, it has no effect on existing LDP sessions. New LDP sessions that are established can perform MPLS LDP GR.
 Note | You can also issue the mpls label protocol ldp command in global configuration mode, which enables LDP on all interfaces configured for MPLS. |
1.
enable
2.
configure
terminal
3.
ip
cef
distributed
4.
mpls
ldp
graceful-restart
5.
interface
type
slot
/
subslot
/
port
[.
subinterface-number]
6.
mpls
ip
7.
mpls
label
protocol
ldp
8.
exit
9.
exit
DETAILED STEPS
Verifying the MPLS LDP Graceful Restart Configuration
To verify that MPLS LDP Graceful Restart is configured correctly, perform the following task.
1.
enable
2.
show
mpls
ldp
neighbor
graceful
restart
3.
show
mpls
ldp
graceful-restart
4.
exit
DETAILED STEPS
| Step 1 |
enable
Use this command to enable privileged ECEC mode. Enter your password if prompted. For example: Example: Router>? enable Router# |
| Step 2 |
show
mpls
ldp
neighbor
graceful
restart
Use this command to display graceful restart information for LDP sessions. For example: Example:
Router# show mpls ldp neighbor graceful restart
Peer LDP Ident: 10.20.20.20:0; Local LDP Ident 10.17.17.17:0
TCP connection: 10.20.20.20.16510 - 10.17.17.17.646
State: Oper; Msgs sent/rcvd: 8/18; Downstream
Up time: 00:04:39
Graceful Restart enabled; Peer reconnect time (msecs): 120000
Peer LDP Ident: 10.19.19.19:0; Local LDP Ident 10.17.17.17:0
TCP connection: 10.19.19.19.11007 - 10.17.17.17.646
State: Oper; Msgs sent/rcvd: 8/38; Downstream
Up time: 00:04:30
Graceful Restart enabled; Peer reconnect time (msecs): 120000
|
| Step 3 |
show
mpls
ldp
graceful-restart
Use this command to display graceful restart sessions and session parameters. For example: Example:
Router# show mpls ldp graceful-restart
LDP Graceful Restart is enabled
Neighbor Liveness Timer: 5 seconds
Max Recovery Time: 200 seconds
Down Neighbor Database (0 records):
Graceful Restart-enabled Sessions:
VRF default:
Peer LDP Ident: 10.18.18.18:0, State: estab
Peer LDP Ident: 10.17.17.17:0, State: estab
|
| Step 4 |
exit
Use this command to exit to user EXEC mode. For example: Example: Router# exit Router> |
Configuration Examples for MPLS LDP Graceful Restart
Configuring MPLS LDP Graceful Restart Example
The figure below shows a configuration where MPLS LDP GR is enabled on Router 1 and MPLS LDP SSO/NSF is enabled on Routers 2 and 3. In this configuration example, Router 1 creates an LDP session with Router 2. Router 1 also creates a targeted session with Router 3 through a traffic engineering tunnel using Router 2.
Router 1 configured with LDP GR:
!
ip subnet-zero
ip cef
mpls label range 16 10000 static 10001 1048575
mpls label protocol ldp
mpls ldp logging neighbor-changes
mpls ldp graceful-restart
mpls traffic-eng tunnels
no mpls traffic-eng auto-bw timers frequency 0
mpls ldp router-id Loopback0 force
!
interface Loopback0
ip address 20.20.20.20 255.255.255.255
no ip directed-broadcast
no ip mroute-cache
!
interface Tunnel1
ip unnumbered Loopback0
no ip directed-broadcast
mpls label protocol ldp
mpls ip
tunnel destination 19.19.19.19
tunnel mode mpls traffic-eng
tunnel mpls traffic-eng autoroute announce
tunnel mpls traffic-eng priority 7 7
tunnel mpls traffic-eng bandwidth 500
tunnel mpls traffic-eng path-option 1 dynamic
!
interface ATM5/1/0
no ip address
no ip directed-broadcast
atm clock INTERNAL
no atm enable-ilmi-trap
no atm ilmi-keepalive
!
interface ATM5/1/0.5 point-to-point
ip address 10.12.0.2 255.0.0.0
no ip directed-broadcast
no atm enable-ilmi-trap
pvc 6/100
encapsulation aal5snap
mpls label protocol ldp
mpls traffic-eng tunnels
mpls ip
ip rsvp bandwidth 1000
!
router ospf 100
log-adjacency-changes
redistribute connected
network 10.12.0.0 0.255.255.255 area 100
network 10.20.20.20 0.0.0.0 area 100
mpls traffic-eng router-id Loopback0
mpls traffic-eng area 100
Router 2 configured with LDP SSO/NSF:
! redundancy mode sso ! ip cef no ip domain-lookup mpls label range 17 10000 static 10001 1048575 mpls label protocol ldp mpls ldp logging neighbor-changes mpls ldp graceful-restart mpls traffic-eng tunnels no mpls traffic-eng auto-bw timers frequency 0 no mpls advertise-labels mpls ldp router-id Loopback0 force ! interface Loopback0 ip address 10.17.17.17 255.255.255.255 no ip directed-broadcast ! interface ATM4/0/0 no ip address no ip directed-broadcast no ip mroute-cache atm clock INTERNAL atm sonet stm-1 no atm enable-ilmi-trap no atm ilmi-keepalive ! interface ATM4/0/0.5 point-to-point ip address 10.12.0.1 255.0.0.0 no ip directed-broadcast no atm enable-ilmi-trap pvc 6/100 encapsulation aal5snap mpls label protocol ldp mpls traffic-eng tunnels mpls ip ip rsvp bandwidth 1000 ! interface POS5/1/0 ip address 10.11.0.1 255.0.0.0 no ip directed-broadcast encapsulation ppp mpls label protocol ldp mpls traffic-eng tunnels mpls ip no peer neighbor-route clock source internal ip rsvp bandwidth 1000 ! router ospf 100 log-adjacency-changes redistribute connected nsf enforce global network 10.11.0.0 0.255.255.255 area 100 network 10.12.0.0 0.255.255.255 area 100 network 10.17.17.17 0.0.0.0 area 100 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 100 ! ip classless
Router 3 configured with LDP SSO/NSF:
! redundancy mode sso ! ip subnet-zero ip cef ! no ip finger no ip domain-lookup mpls label protocol ldp mpls ldp neighbor 10.11.11.11 targeted ldp mpls ldp logging neighbor-changes mpls ldp graceful-restart mpls traffic-eng tunnels no mpls traffic-eng auto-bw timers frequency 0 mpls ldp discovery directed-hello interval 12 mpls ldp discovery directed-hello holdtime 130 mpls ldp discovery directed-hello accept mpls ldp router-id Loopback0 force ! interface Loopback0 ip address 10.19.19.19 255.255.255.255 no ip directed-broadcast ! interface POS1/0 ip address 10.11.0.2 255.0.0.0 no ip directed-broadcast encapsulation ppp mpls label protocol ldp mpls traffic-eng tunnels mpls ip no peer neighbor-route clock source internal ip rsvp bandwidth 1000 ! router ospf 100 log-adjacency-changes redistribute connected nsf enforce global network 10.11.0.0 0.255.255.255 area 100 network 10.19.19.19 0.0.0.0 area 100 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 100 ! ip classless
Additional References
The following sections provide references related to MPLS LDP GR.
Related Documents
|
Related Topic |
Document Title |
|---|---|
|
MPLS Label Distribution Protocol |
MPLS Label Distribution Protocol (LDP) |
|
LDP commands |
Cisco IOS Multiprotocol Label Switching Command Reference |
Standards
|
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 |
MIBs Link |
|---|---|
|
MPLS Label Distribution Protocol MIB Version 8 Upgrade |
To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
|
RFCs |
Title |
|---|---|
|
RFC 3036 |
LDP Specification |
|
RFC 3478 |
Graceful Restart Mechanism for Label Distribution |
Technical Assistance
|
Description |
Link |
|---|---|
|
The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password. |
Feature Information for MPLS LDP Graceful Restart
The 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 . An account on Cisco.com is not required.|
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
MPLS LDP Graceful Restart |
Cisco IOS XE Release 2.1 |
When a router is configured with Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) Graceful Restart (GR), it assists a neighboring router that has MPLS LDP Stateful Switchover/Nonstop Forwarding (SSO/NSF) Support and Graceful Restart to recover gracefully from an interruption in service. MPLS LDP GR functions strictly in helper mode, which means it can only help other routers that are enabled with MPLS SSO/NSF and GR to recover. If the router with LDP GR fails, its peer routers cannot help the router recover. In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers. The following commands were introduced or modified: debugmplsldpgraceful-restart, mplsldpgraceful-restart, mplsldpgraceful-restarttimersmax-recovery, mplsldpgraceful-restarttimersneighbor-liveness, showmplsipbinding, showmplsldpbindings, showmplsldpgraceful-restart, showmplsldpneighbor. |