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Webcast-Catalyst9k
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HSRP and lost routes

I have designed a two router (6509) environment with multiple VLANs. To load balance I have split the VLAN (odd/even) between the 6509s. The 6509s are connected via a unique Layer 3 trunk. EIGRP is being used.

As I understand it, when I detach an uplink from a VLAN, the interface on its 6509 will drop and the routing entry will be dropped on that router. If it turns out that this was the Active Router, the Standby will take over.

Now in a ODD/EVEN VLAN split, if I drop an interface on a STANDBY router, all VLANs that use this router as the ACTIVE will NOT see a route to the detached VLAN. The route table will show no entry as the interface is down, even thought the VLAN is active on the other router.

Assuming I am correct in this discription (in tests we lost connectivity when the standby interface was pulled), how do I get EIGRP to see there is a route to the "missing" VLAN via the other router?

1 REPLY
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Re: HSRP and lost routes

Don't mix routing and HSRP up--the operation of HSRP should have nothing to do with your routing protocol, and the operation of the routing protocol should not have anything to do with HSRP. In this case, if the two routers are neighbors, or are receiving each other's routes through the network, then when one router's link to the common subnet fails, it should still see the subnet as reachable through another link to the other router, or through a neighbor that leads towards the core of the network.

If you aren't seeing this, then there is something going on with routing we need to look at--with the link between the routers down, I would look at the remaning neighbors available, and try to figure out which one I would have expected to learn the route that I'm no longer connected to through. I would then work my way back to the router that is still connected to the link I've lost connectivity to, and try to figure out where the information isn't being pushed through.

:-)

Russ.W

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