CCNP TSHOOT 6.0 - The Cisco Learning Network

CCNPv6 TSHOOT
Sample First Hop Redundancy
Troubleshooting Flow
Determine if
outages are
caused by
FHRP or
other
protocols
Determine if
FHRP
addresses
are used by
hosts
Verify Layer 3
connectivity
between routers
Investigate
FHRP
router-toroutercommunication
Investigate
FHRP role
selection
Verify reception of
FHRP messages
© 2009 Cisco Systems, Inc. All rights reserved. TSHOOT v1.0—41
Many problems with FHRPs are caused by underlying problems in the Layer 3 connectivity between the routers.
Therefore, a good next-step in the troubleshooting process is to verify that there is Layer 3 connectivity between
all routers that are participating in the FHRP. Ping from each of the participating routers to the IP addresses of the
other participating routers. If one of these pings fail, start a troubleshooting process to diagnose and resolve the
Layer 3 connectivity issues between the routers before further investigating the FHRP.
When you have confirmed that there is Layer 3 connectivity between the participating routers in general, you must
verify the proper transmission and reception of FHRP packets. To limit potential disruption, always use show
commands to gather information before using debug commands.
Verify Reception of FHRP Messages
DLS1#show standby vlan 100 brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vl100 100 110 P Active local 10.1.100.253 10.1.100.254
DLS2#show standby vlan 100 brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vl100 100 100 P Standby 10.1.100.252 local 10.1.100.254
This example shows how to confirm proper transmission and reception of HSRP messages. For GLBP or VRRP,
the procedure is similar, although the command output is slightly different.
To confirm the proper reception of HSRP messages on all routers in the group, verify that all routers list an active
and a standby router and that these roles are listed in a consistent way across all the routers. The show
standby brief command is concise and still shows the most relevant information. As you can see in the
example, switch DLS2 lists the IP address of switch DLS1 as the active router. As the standby router, it lists
“local” to indicate that it considers itself to be the standby router. On switch DLS1, the situation is the opposite:
The address of switch DLS2 is listed as the standby address, while the active router is listed as local. While you
are verifying these roles, this is also a good opportunity to confirm that both the standby group number and the
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