I am having a problem with HSRP routers occasionally becoming active-active.
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. This configuration has worked for almost two years now without having this issue. I am not sure if BGP has something to do with this as we has just started after recent implementation of BGP routing with our ISP
Attached is the output of "sh ip int " + "sh cdp ne" + sh span" from a different router that had the same problem.
So, Router 1 loses connection to the access switch. When I check the CDP neighbour, the router is unable to detect the switch. The router port to the switch is up/up and spanning tree status is forwarding but unable to ping the access switch.
During times when the issue is happening, the access switch can sometimes see the router in cdp neighbor, the interface to the router is up/up and spanning tree status of the port is forwarding.
Sometimes when I reset the port on the router, the link will be re-established but it will go down again after about 45 seconds.
Reloading the router1 will fix the problem but it appears that the HWIC-4ESW become dumb every few weeks.
If I show the arp on the router, it will say that the mac address to the switch is "incomplete"
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