Specifications

Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
RC-178
Cisco IOS XR Routing Configuration Guide
MPLS LDP-IGP Synchronization Compatibility with LDP Graceful Restart
LDP graceful restart protects traffic when an LDP session is lost. If a graceful restart-enabled LDP
session fails, MPLS LDP IS-IS synchronization is still achieved on the interface while it is protected by
graceful restart. MPLS LDP IGP synchronization is eventually lost under the following circumstances:
• LDP fails to restart before the LDP graceful restart reconnect timer expires.
• The LDP session on the protected interface fails to recover before the LDP graceful restart recovery
timer expires.
MPLS LDP-IGP Synchronization Compatibility with IGP Nonstop Forwarding
IS-IS nonstop forwarding (NSF) protects traffic during IS-IS process restarts and route processor (RP)
failovers. LDP IS-IS synchronization is supported with IS-IS NSF only if LDP graceful restart is also
enabled over the interface. If IS-IS NSF is not enabled, the LDP synchronization state is not retained
across restarts and failovers.
Label Distribution Protocol IGP Auto-configuration
Label Distribution Protocol (LDP) Interior Gateway Protocol (IGP) auto-configuration simplifies the
procedure to enable LDP on a set of interfaces used by an IGP instance. LDP IGP auto-configuration can
be used on a large number interfaces (for example, when LDP is used for transport in the core) and on
multiple IGP instances simultaneously.
This feature supports the IPv4 address family for the default VPN routing and forwarding (VRF)
instance.
LDP IGP auto-configuration can also be explicitly disabled on individual interfaces under LDP using the
igp auto-config disable command. This allows LDP to receive all IGP interfaces except the ones
explicitly disabled.
See Cisco IOS XR Multiprotocol Label Switching Configuration Guide for information on configuring
LDP IGP auto-configuration.
MPLS TE Forwarding Adjacency
MPLS TE forwarding adjacency allows a network administrator to handle a traffic engineering, label
switch path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network, based on the Shortest
Path First (SPF) algorithm. A forwarding adjacency can be created between routers in the same IS-IS
level. 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 cost of the link 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.
MPLS TE forwarding adjacency is considered in IS-IS SPF only if a two-way connectivity check is
achieved. This is possible if the forwarding adjacency is bidirectional or the head end and tail end routers
of the MPLS TE tunnel are adjacent.
The MPLS TE forwarding adjacency feature is supported by IS-IS. For details on configuring MPLS TE
forwarding adjacency, see Cisco IOS XR Multiprotocol Label Switching Configuration Guide.