Eigrp Nonstop Forwarding - Cisco Catalyst 9500 series Configuration Manual

EIGRP Nonstop Forwarding

EIGRP Nonstop Forwarding
The Device supports two levels of EIGRP nonstop forwarding:
• EIGRP NSF Awareness
• EIGRP NSF Capability
EIGRP NSF Awareness
The Network Advantage license supports EIGRP NSF Awareness for IPv4. When the neighboring router is
NSF-capable, the Layer 3 Device continues to forward packets from the neighboring router during the interval
between the primary Route Processor (RP) in a router failing and the backup RP taking over, or while the
primary RP is manually reloaded for a nondisruptive software upgrade.
This feature cannot be disabled. For more information on this feature, see the "EIGRP Nonstop Forwarding
(NSF) Awareness" section of the Cisco IOS IP Routing Protocols Configuration Guide, Release 12.4.
EIGRP NSF Capability
The Network Advantage license supports EIGRP Cisco NSF routing to speed up convergence and to eliminate
traffic loss after a stack master change. For details about this NSF capability, see the "Configuring Nonstop
Forwarding" chapter in the High Availability Configuration Guide, Cisco IOS XE Release 3S.
The Network Advantage license also supports EIGRP NSF-capable routing for IPv4 for better convergence
and lower traffic loss following a stack master change. When an EIGRP NSF-capable stack master restarts
or a new stack master starts up and NSF restarts, the Device has no neighbors, and the topology table is empty.
The Device must bring up the interfaces, reacquire neighbors, and rebuild the topology and routing tables
without interrupting the traffic directed toward the Device stack. EIGRP peer routers maintain the routes
learned from the new stack master and continue forwarding traffic through the NSF restart process.
To prevent an adjacency reset by the neighbors, the new stack master uses a new Restart (RS) bit in the EIGRP
packet header to show the restart. When the neighbor receives this, it synchronizes the stack in its peer list
and maintains the adjacency with the stack. The neighbor then sends its topology table to the stack master
with the RS bit set to show that it is NSF-aware and is aiding the new stack master.
If at least one of the stack peer neighbors is NSF-aware, the stack master receives updates and rebuilds its
database. Each NSF-aware neighbor sends an end of table (EOT) marker in the last update packet to mark the
end of the table content. The stack master recognizes the convergence when it receives the EOT marker, and
it then begins sending updates. When the stack master has received all EOT markers from its neighbors or
when the NSF converge timer expires, EIGRP notifies the routing information database (RIB) of convergence
and floods its topology table to all NSF-aware peers.
EIGRP Stub Routing
The EIGRP stub routing feature reduces resource utilization by moving routed traffic closer to the end user.
Routing Configuration Guide, Cisco IOS XE Everest 16.6.x (Catalyst 9500 Switches)
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Configuring IP Unicast Routing