how does hsrp/eigrp work in this scenario

Unanswered Question
Dec 12th, 2009


I have a site with 2 routers, 1 x 10meg ethernet and 1 x  2 meg e1 for backup, they are using hsrp and are tracking the reachabilty of a route on both router. they are also using eigrp. they both connect to a remote datacentre.

If I unplug the lan port from the primary router, what would happen, would the backup router learn the route via the primary routers lan port originally? and then track that and it if goes down, it would use the feasible route from its own e1 wan interface?, and would both routers be hsrp active at this time as they cannot see each others hello's ?


I have this problem too.
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Giuseppe Larosa Sat, 12/12/2009 - 09:26

Hello Carl,

the question is wise.

if both are tracking the presence of a route in the IP routing table with a tracking object AND if EIGRP is running on all links of interest, (primary WAN link 10 Mbps, secondary WAN E1 link, and internal Vlan(s)) the monitored route will no disappear but the route on the secondary path will be installed.

As a result of this primary router will still be the HSRP active.

R1 will have its route via R2, so it may start to send ICMP redirect to each client trying to use it to reach the remote network.

If ICMP redirect sending is disabled R1 has to resend all packets received by clients to R2.

I would suggest to track the state of the primary WAN interface on the primary router and of the E1 link on the secondary router. IF EIGRP is running on all links of interest it can deal with topology changes and in this way HSRP active follows the device with the best path to the remote datacenter.

Actually, with my proposal when primary link fails HSRP priority of R1 is reduced and R2 takes over.

With default settings priority is reduced by 10 so have configured priorities that differ of less then 10 like 105 and 100.

The command preempt is needed to have the desired behaviour or  R2 cannot take over even if its priority 100 is greater then 105-10=95

This is an important point.

The only case when both routers claim to be active for an HSRP group is if they don't see each other HSRP hellos. This may happen in case of a failure in the internal lan switch(es) or a bridging loop.

When the fault is in one WAN interface primary router

Hope to help



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