Isis Nsr; Multi-Instance Is-Is; Multiprotocol Label Switching Traffic Engineering; Overload Bit On Router - Cisco ASR 9000 Series Routing Configuration Manual

ISIS NSR

If you configure IETF NSF on the Cisco IOS XR router and a neighbor router does not support IETF NSF,
Note
the affected adjacencies flap, but nonstop forwarding is maintained to all neighbors that do support IETF
NSF. A restart reverts to a cold start if no neighbors support IETF NSF.
ISIS NSR
Non Stop Routing suppresses routing changes on peers to SSO-enabled devices during processor switchover
events (SSO or ISSU), reducing network instability and downtime. Non Stop Routing allows for the forwarding
of data packets to continue along known routes while the routing protocol information is being restored
following a processor switchover. When Non Stop Routing is used, peer networking devices have no knowledge
of any event on the switching over router. All information needed to continue the routing protocol peering
state is transferred to the standby processor, so it can continue immediately upon a switchover.
Under NSR mode, ISIS processes running on standby sync information with ISIS processes running on active
and maintains same set of isis neighbors, lsp databases, tunnels, etc. This reduces the startup time for ISIS
process to become fully operational after the switchover, which can be very useful in a scale environment.

Multi-Instance IS-IS

You can configure up to eight IS-IS instances. MPLS can run on multiple IS-IS processes as long as the
processes run on different sets of interfaces. Each interface may be associated with only a single IS-IS instance.
Cisco IOS XR software prevents the double-booking of an interface by two instances at configuration time—two
instances of MPLS configuration causes an error.
Because the Routing Information Base (RIB) treats each of the IS-IS instances as equal routing clients, you
must be careful when redistributing routes between IS-IS instances. The RIB does not know to prefer Level
1 routes over Level 2 routes. For this reason, if you are running Level 1 and Level 2 instances, you must
enforce the preference by configuring different administrative distances for the two instances.

Multiprotocol Label Switching Traffic Engineering

The MPLS TE feature enables an MPLS backbone to replicate and expand the traffic engineering capabilities
of Layer 2 ATM and Frame Relay networks. MPLS is an integration of Layer 2 and Layer 3 technologies.
For IS-IS, MPLS TE automatically establishes and maintains MPLS TE label-switched paths across the
backbone by using Resource Reservation Protocol (RSVP). The route that a label-switched path uses is
determined by the label-switched paths resource requirements and network resources, such as bandwidth.
Available resources are flooded by using special IS-IS TLV extensions in the IS-IS. The label-switched paths
are explicit routes and are referred to as traffic engineering (TE) tunnels.

Overload Bit on Router

The overload bit is a special bit of state information that is included in an LSP of the router. If the bit is set
on the router, it notifies routers in the area that the router is not available for transit traffic. This capability is
useful in four situations:
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
348
Implementing IS-IS