Anycast IP Gateway routers use TLV 187 to advertise the configured routing interfaces. You must associate the routing interfaces with Layer 2 VSNs, and configure each Anycast IP Gateway-enabled interface with a gateway IP and a gateway MAC.
The gateway MAC uses the VRRP MAC address format with the virtual router ID (VRID) in the last byte, 00:00:5e:00:01:xx. The gateway MAC must be the same on different routers for the same associated Layer 2 VSN. Different interfaces can share the gateway MAC. As a best practice, use the same VRID on different interfaces whenever possible.
You can configure a different gateway IP from the VLAN IP, or as a One IP interface, which uses the same IP as the VLAN. The gateway IP must be in different subnets for different interfaces, and must be the same on different routers for the same associated Layer 2 VSNs.
The BEB floods broadcast ARP queries for the Anycast IP Gateway address to all routers. Anycast IP Gateway routers can also issue ARP queries in the subnets of the routing interfaces. For ARP queries initiated by Anycast IP Gateway routers, the sender hardware address (MAC address) and sender protocol address (IP address) differ by scenario. The following table provides details for each scenario.
| Scenario | Ethernet Source Address | Sender Hardware Address | Sender Protocol Address |
|---|---|---|---|
| ARP reply | VLAN chassis MAC | GW MAC | GW IP |
| ARP query non One IP | VLAN chassis MAC | VLAN chassis MAC | VLAN IP |
| ARP query One IP without CLIP | VLAN chassis MAC | VLAN chassis MAC | 0.0.0.0 |
| ARP query One IP with CIP | VLAN chassis MAC | VLAN chassis MAC | CLIP IP |
BEBs process the I-SID Attributes TLVs that contain Anycast IP Gateway information advertised by routers for each locally-created Layer 2 VSN, and install a static MAC entry for the gateway MAC with the next hop of the closest router based on SPB cost. BEBs do not dynamically learn the gateway MAC. If multiple gateway routers are reachable with the same SPB cost, the BEB makes the selection based on the IS-IS system ID:
If a vIST node advertises the routing interface TLV, the next-hop BMAC for the static MAC entry is the virtual BMAC of the cluster. If only one of the vIST peers is configured as a router, then the other peer always selects its peer as the next-hop, regardless of the SPB cost.
Multi-area SPB boundary nodes can redistribute I-SID Attributes TLVs if you enable the Multi-area SPB Layer 2 VSN redistribution policy . The TLVs contain a metric field to advertise the SPB cost from a physical node to the Multi-area SPB virtual node to compare against the cost of routers in the local area.
The designated boundary node only redistributes the routing information for its closest Anycast IP Gateway router to the other SPB area for each Layer 2 VSN.