I have an issue with HSRP routers occasionally becoming active-active in our branch networks.
The site has two 1921 routers with HWIC-4ESW each and connect to Catalyst 2960 Access switches. Router1 is normally the active router and Router2 the standby router.
Occasionally, Router1 loses connectivity to the access switch, so Router 2 does not get any HSRP response from Router 1 and becomes active router as well, creating an active-active scenario.
Router1 port Fa0/0/0 stays forwarding though it is unable to reach Access switch 1. If I run show CDP neighbour, the router is unable to see the Switch1 (CDP is running on both router and switch).
Access Switch1 port F0/1 is also forwarding but unable to ping router 1. It can see Router 1 when I run show CDP neighbour.
If I bounce the ports, they will see each other for a about 45 seconds then drop the connection again.
The only way to restore the connection and fix the HSRP active-active router scenario is to reboot Router 1.
This happens is randomly in several branches with the same topology once to twice a month. The configuration has worked fine with no issues for over a year. I am not sure if this has anything to do with BGP since this issue started after we implemented BGP routing with our ISPs.
