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VRRP flapping between two routers in same switch

Hi people

I have a problem with VRRP or maybe spanning tree, I'm not sure yet and need some input.

My two 1921 routers are connected to a 3750-E stack of two switches where the different routers are connected with two trunk interfaces to one switch each. Both physical interface on the routers are configured with sub interfaces having separate VRRP groups. The attached image is a quick illustration of the setup.

A few times every hour I get log entries on Router2 saying it has become VRRP master of all VRRP groups and then a few seconds later VRRP backup again. I understand it would be a STP problem if the routers where physically distant with trunks between them but they are in the stame switch stack. The 3750 stack does however log MACFLAP_NOTIF on the VRRP MAC addresses when the flapping occurs.

Below is an example of the interface config on most of the flapping interfaces. Any ideas?

 

Router1

interface GigabitEthernet0/1.404
 description DMZ
 encapsulation dot1Q 404
 ip address 192.168.34.1 255.255.255.0
 ip flow ingress
 ip flow egress
 ip virtual-reassembly in
 vrrp 34 ip 192.168.34.1
 

Router2

interface GigabitEthernet0/1.404
 description DMZ
 encapsulation dot1Q 404
 ip address 192.168.34.2 255.255.255.0
 ip access-group DMZ in
 ip flow ingress
 ip flow egress
 vrrp 34 ip 192.168.34.1

 

Regards

Fredrik

  • LAN Switching and Routing
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