Mpls Label Distribution Protocol Igp Synchronization; Configuring Mpls Ldp Is-Is Synchronization - Cisco NCS 5500 Series Configuration Manuals

MPLS Label Distribution Protocol IGP Synchronization

Step 13
show isis [ instance instance-id ] neighbors [ interface-type interface-instance ] [ summary ] [ detail ] [ systemid
system-id ]
Example:
RP/0/RP0/CPU0:router# show isis neighbors summary
(Optional) Displays information about IS-IS neighbors.
MPLS Label Distribution Protocol IGP Synchronization
Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) Interior Gateway Protocol (IGP)
Synchronization ensures that LDP has completed label exchange before the IGP path is used for switching.
MPLS traffic loss can occur in the following two situations:
• When an IGP adjacency is established, the router begins forwarding packets using the new adjacency
• When an LDP session closes, the router continues to forward traffic using the link associated with the
This feature provides a mechanism to synchronize LDP and IS-IS to minimize MPLS packet loss. The
synchronization is accomplished by changing the link metric for a neighbor IS-IS link-state packet (LSP),
based on the state of the LDP session.
When an IS-IS adjacency is established on a link but the LDP session is lost or LDP has not yet completed
exchanging labels, IS-IS advertises the maximum metric on that link. In this instance, LDP IS-IS synchronization
is not yet achieved.
Note In IS-IS, a link with a maximum wide metric (0xFFFFFF) is not considered for shortest path first (SPF).
Therefore, the maximum wide metric of -1 (0XFFFFFE) is used with MPLS LDP IGP synchronization.
When LDP IS-IS synchronization is achieved, IS-IS advertises a regular (configured or default) metric on
that link.

Configuring MPLS LDP IS-IS Synchronization

This task explains how to enable Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP)
IS-IS synchronization. MPLS LDP synchronization can be enabled for an address family under interface
configuration mode. Only IPv4 unicast address family is supported. This task is optional.
SUMMARY STEPS
1. configure
2. router isis instance-id
3. interface type interface-path-id
4. address-family ipv4 unicast
5. mpls ldp sync [ level { 1 | 2 }]
6. commit
Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x
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before LDP has exchanged labels with peers on that link.
LDP peer rather than using an alternate path with an established LDP session.
Implementing IS-IS