Tunnel Concentrator supports ARP Responder by default. Tunnel Concentrator stores its own local ARP lookup table and can proxy and respond to ARP requests. No configuration is required to enable this feature
To update its ARP table, Tunnel Concentrator uses the following logic:
Tunnel Concentrator updates its ARP table using IP address - MAC address mappings that it learns from DHCP packets, or from the source IP address of packets that ingress over a GRE tunnel.
Tunnel Concentrator does not store mappings that it learns from the bridged portion of the network.
To respond to ARP requests, Tunnel Concentrator does a lookup of its ARP table for a MAC address that maps to the target IP address from the ARP request and responds as per these rules:
If the ARP lookup succeeds, Tunnel Concentrator returns an ARP response to the sender directly with the correct MAC address.
If the ARP lookup fails, Tunnel Concentrator forwards the ARP broadcast to the bridged network. Tunnel Concentrator does not forward ARP broadcasts to GRE tunnels.