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Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
RC-276
Cisco IOS XR Routing Configuration Guide
OL-14356-01
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.
MPLS TE Interarea Tunnels
MPLS TE interarea tunnels allow you to establish MPLS TE tunnels that span multiple IGP areas (Open
Shorted Path First [OSPF]) and levels (IS-IS), removing the restriction that required that both the tunnel
headend and tailend routers be in the same area. The IGP can be either IS-IS or OSPF. See the
“Configuring MPLS Traffic Engineering for IS-IS” section on page RC-295 for information on
configuring MPLS TE for IS-IS.
For details on configuring MPLS TE interarea tunnels, see Cisco IOS XR Multiprotocol Label Switching
Configuration Guide.
IP Fast Reroute
The IP Fast Reroute (IPFRR) loop-free alternate (LFA) computation provides protection against link
failure. Locally computed repair paths are used to prevent packet loss caused by loops that occur during
network reconvergence after a failure. See IETF draft-ietf-rtgwg-ipfrr-framework-06.txt and
draft-ietf-rtgwg-lf-conv-frmwk-00.txt for detailed information on IPFRR LFA.