The tunnel source interface
address should be an interface that is set up to be reachable from receivers
under all instances. You can use a physical interface address, but it can cause
the tunnel to go down if that physical interface is down. A loopback interface
is recommended to sustain availability. You do not need a separate loopback
address, you can reuse the loopback interface that you usually would have to
carry router and router-ID IP address (usually Loopback 0).
IP PIM passive is the recommended and supported mode on AMT interfaces
to enable IP multicast routing for AMT tunnel interfaces. This is recommended
since no PIM messages (only AMT/IGMP messages) will be sent or received via the
On an AMT relay, you need only one tunnel interface to which all
gateways can connect. Therefore the interface is a multipoint interface. Every
gateway interface can only connect to one relay, but you can configure multiple
Even though AMT tunnels (relay and gateway) only support IPv4 tunnels,
the IPv4 tunnels can carry both IPv4 and IPv6 simultaneously. You can configure
the AMT for the version(s) of IP that you need.
If you want to set up a redundant AMT relay, your AMT relay address
configured on the gateway should be any IP address that you set up as an
anycast address on your relays. If you do not plan to use redundant (Anycast)
Relay, you can use the relays tunnel source address on the gateways.
If you shut down the anycast Loopback interface, the AMT relay would not
accept new AMT gateway tunnel requests. IP routing for the anycast address
would only point to any other relays active with the same address and new
requests would therefore go to those relays. Any AMT gateways already connected
to this relay would stay on this relay, because they already are using the
relays interface address.