Can we use same VRID (VRRP instance) for both IPv4 and IPv6 virtual router in VRRP or VRRP-E?
In a layer-3 router, we have requirement to configure interface VE with both IPv4 and IPv6 gateways with same VRID in VRRP-E.
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Yes. The VRID field is an 8-bit field in the VRRP packet, which makes up part of the virtual MAC address. A network interface will have the same MAC address for both IPv4 and IPv6, which are completely separate layer-3 protocols. IPv4 and IPv6 VRRP packets are not interoperable, and an IPv4 VRRP packet can have the same VRID as an IPv6 VRRP packet.
What VRRP is really doing is fooling the hosts on a network at layer-2 (MAC address). When a host uses ARP in IPv4, or ND in IPv6 to determine the MAC address of its configured gateway (the virtual IP address), VRRP will return a virtual MAC address. Traffic destined for the configured gateway will be encapsulated at layer-2 with the (virtual) destination MAC address.