VRRP - using the same ID on subinterfaces
When implementing an FHRP solution using VRRP, it is possible to use the same VRRP ID number on different physical interfaces as indicated in this note about using the same ID on different interfaces.
However, in more recent versions of IOS, it seems that it is not possible to do so on subinterfaces of the same physical interface. For example, the following is the result of attempting to do so:
R1(config)#int gi 0/0.1 R1(config-subif)#encapsulation dot1Q 10 R1(config-subif)#ip address 192.168.1.1 255.255.255.0 R1(config-subif)#vrrp 10 ip 192.168.1.254 R1(config-subif)#exit R1(config)#int gi 0/0.2 R1(config-subif)#encapsulation dot1Q 20 R1(config-subif)#ip address 192.168.2.1 255.255.255.0 R1(config-subif)#vrrp 10 ip 192.168.2.254 % Cannot create new VRRP group
The error message does not indicate the reason for not being able to create the new VRRP group.
However, the reason does seem to be because the same VRRP ID is being used on multiple subinterfaces of the same physical interface. If you attempt to use the same VRRP ID on different physical interfaces it will be successful.
The above was tested using IOSv Version 15.9(3)M6 on Cisco's CML platform. It may be that in previous versions of IOS this was possible and this is why we see it in Cisco documentation, but it has changed in the more recent versions.