Eigrp Nonstop Forwarding - Cisco 3750G - Catalyst Integrated Wireless LAN Controller Configuration Manual

Configuring EIGRP

EIGRP Nonstop Forwarding

The switch stack supports two levels of EIGRP nonstop forwarding:
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EIGRP NSF Awareness
The EIGRP NSF Awareness feature is supported for IPv4 in the IP services image, beginning with Cisco
IOS Release 12.2(25)SEC. When the neighboring router is NSF-capable, the Layer 3 switch 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 Feature Guide at this URL:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a0080160010
.html
EIGRP NSF Capability
Beginning with Cisco IOS Release 12.2(35)SE, the IP services image 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 switch
has no neighbors, and the topology table is empty. The switch must bring up the interfaces, reacquire
neighbors, and rebuild the topology and routing tables without interrupting the traffic directed toward
the switch 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.
NSF is not supported on interfaces configured for Hot Standby Router Protocol (HSRP).
Note
Use the nsf EIGRP routing configuration command to enable EIGRP NSF routing. Use the show ip
protocols privileged EXEC command to verify that NSF is enabled on the device. See the command
reference for this release for information about the nsf command.
Catalyst 3750 Switch Software Configuration Guide
35-38
EIGRP NSF Awareness, page 35-38
EIGRP NSF Capability, page 35-38
Chapter 35 Configuring IP Unicast Routing
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