Multicast Mls Nsf With Sso; Routing Protocols - Cisco 7604 Configuration Manual

Understanding NSF with SSO Supervisor Engine Redundancy
supervisor engine signals when the RIB has converged. The software removes all FIB and adjacency
entries that have an epoch older than the current switchover epoch. The FIB now represents the newest
routing protocol forwarding information.

Multicast MLS NSF with SSO

NSF with SSO does not support IPv6 multicast traffic. If you configure support for IPv6 multicast traffic,
Note
configure RPR or RPR+ redundancy.
Multicast multilayer switching (MMLS) NSF with SSO is required so that Layer 3 multicast traffic that
is switched by the router is not dropped during switchover. Without MMLS NSF with SSO, the Layer 3
multicast traffic is dropped until the multicast protocols converge.
During the switchover process, traffic is forwarded using the old database (from the previously active
supervisor engine). After multicast routing protocol convergence has taken place, the shortcuts
downloaded by the newly active MSFC will be merged with the existing flows and marked as new
shortcuts. Stale entries will slowly be purged from the database allowing NSF to function during the
switchover while ensuring a smooth transition to the new cache.
Because multicast routing protocols such as Protocol Independent Multicast (PIM) sparse mode and PIM
dense mode are data driven, multicast packets are leaked to the router during switchover so that the
protocols can converge.
Because the traffic does not need to be forwarded by software for control-driven protocols such as
bidirectional PIM, the router will continue to leak packets using the old cache for these protocols. The
router builds the mroute cache and installs the shortcuts in hardware. After the new routes are learned,
a timer is triggered to go through the database and purge the old flows.
Multicast MLS NSF with SSO requires NSF support in the unicast protocols.
Note

Routing Protocols

The routing protocols run only on the MSFC of the active supervisor engine, and they receive routing
updates from their neighbor routers. Routing protocols do not run on the MSFC of the redundant
supervisor engine. Following a switchover, the routing protocols request that the NSF-aware neighbor
devices send state information to help rebuild the routing tables. Alternately, the IS-IS protocol can be
configured to synchronize state information from the active to the redundant supervisor engine to help
rebuild the routing table on the NSF-capable device in environments where neighbor devices are not
NSF-aware. Cisco NSF supports the BGP, OSPF, IS-IS, and EIGRP protocols
For NSF operation, the routing protocols depend on CEF to continue forwarding packets while the
Note
routing protocols rebuild the routing information.
BGP Operation
When an NSF-capable router begins a BGP session with a BGP peer, it sends an OPEN message to the
peer. Included in the message is a statement that the NSF-capable device has "graceful" restart
capability. Graceful restart is the mechanism by which BGP routing peers avoid a routing flap following
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
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Chapter 7 Configuring NSF with SSO Supervisor Engine Redundancy
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