Enabling Fabric Route Mode on the VRRP Backup Router

Note

On the 7100-Series, Fabric route mode requires an advanced router license. See License Overview for advanced router license details.

The fabric route mode allows a VRRP instance in the backup state to forward IPv4 and IPv6 packets destined for the VRRP MAC address. This feature provides for sharing of the traffic load across VRRP routers.

When fabric route mode is enabled on a VRRP router, the router behavior is exactly as detailed in RFC 5798 with these exceptions:

• Accept-Mode – A VRRP backup router with fabric route mode enabled will respond to ICMP packets it receives that are destined for the virtual gateway. A VRRP instance that wants to allow a non-owner virtual IP address to be pingable must enable the VRRP instance in fabric route mode to respond to ICMP packets using the vrrp accept-mode command.
• Forwarding – The VRRP standard forwarding defines a single VRRP master router and one or more VRRP backup router. Packets arriving on the backup router, destined for the VRRP MAC address, are cross bridged to the VRRP master router. The VRRP master router forwards the packet to the network (see Standard VRRP Forwarding). The VRRP backup router remains in a dormant state and is not allowed to forward any traffic destined to the virtual gateway MAC address.
  

  Standard VRRP Forwarding
  

  

  With VRRP fabric route mode enabled on the backup router, a VRRP master and a backup router are started. Packets arriving on the backup router, destined to the VRRP MAC address, are no longer cross bridged. All IPv4 or IPv6 traffic destined for the VRRP MAC address and received directly on the VRRP backup router enabled for fabric route mode is now forwarded to the network by the backup router (See Fabric Route VRRP Forwarding). All ACL, policy rules, router application services, and routing is applied to the incoming packet.

  

  Fabric Route VRRP Forwarding
  

  
• IPV4 ARP – All broadcast ARP requests are still handled by the VRRP master router except for unicast ARP requests destined for the VRRP MAC address received by the VRRP backup router with fabric route mode enabled. The VRRP backup fabric route mode enabled router processes these requests.
• IPV6 Neighbor Discovery – All neighbor solicitation requests are handled by the VRRP master router, except for unicast neighbor solicitation requests destined for the VRRP MAC address received by the VRRP fabric route mode enabled backup router. The VRRP fabric route mode enabled backup router will process these requests.

Use the vrrp fabric-route-mode command, in interface configuration mode, specifying the VRID the fabric mode is applied to, to enable fabric route mode on the VRRP router. This command can be applied to both the VRRP master and backup routers, but will only be operational on the VRRP backup router.

Use the show running-config command, specifying the interface the VRRP router is configured on, to display determine whether VRRP fabric route mode has been configured on the router.