HSRP or L3 issue

[mrshabbs]

Whilst carrying out resilience testing to confirm igp/ebgp multipath is working, I have stumbled upon the below issue.

The attached sketch crudely shows the topolgy of the network. 2 cores with a cross connect running ibgp, from each of the cores I have 1 link to each Dist switch, 4 links in total running ebgp. Between the Dist switches I have a L2 trunk link.

Under normal operation, when pinging a client in vlan 10, traffic flows through C1 to D1 (active hsrp for vlan 10). To confirm multipath, I shutdown the 3 p2p links, C1toD1, C1toD2, C2toD1. Traffic should then be routed C1 to C2 to D2 to D1, or so I thought. Shutting down the 3 links results in a loss of connectivity to the client in Vlan 10. If the L2 ort-channel between D1&D2 is then also broken, traffic is restored.

I can only think that this interruption to traffic is because of hsrp, D1 remains active until the port-channel is broken.
I was expecting hsrp to take care of this, i.e. traffic would flow D1 to D2 to C2 to C1?

I am also wondering if the lack of a L3 ibgp p2p link between D1 & D2 is also contributing to the loss of connectivity, i.e. no route from D1 to D2 to C2 to C1.

Any help much appreciated!!

Thanks

[Muhammad Awais Khan]

Hi,

After reviewing your above scenario, it seems you are not using HSRP tracking feature. Without HSRP tracking, the passive or backup SVI on your devices will become active only if that particular Vlan lets say in your example Vlan 10 goes down. With tracking, you can monitor the state of the directly connected interface and whenever interface went down then priority of active HSRP VLAN will become down by 10 which can force passive HSRP to take over if you define priorities well.

If thats the case, i would recommend you to review below doc for HSRP with object tracking:

https://www.cisco.com/c/en/us/td/docs/switches/blades/3040/software/release/12-2_44_se/configuration/guide/swhsrp.html#wp1083959

[i.hughes]

The HSRP config would be useful, have you tracking, pre-empting etc set