I have created a GRE tunnel between a 460g2 and another device.
I have configured a /31 on the GRE tunnel.
I have enabled forwarding on the GRE tunnel.
I am only able to ping the remote side of the tunnel from the 460 itself. I can ping using its IP of the tunnel as the source, or using another (loopback) IP of the 460 as the source.
From a 480 connected to the 460, I can ping the 460's tunnel IP, but not the remote IP. Watching the traffic counters and sniffing on the remote device shows that packets are not even entering the tunnel, so I assume the 460 is not forwarding traffic (that doesn't originate with itself).
This seems to be the same symptoms of when a VLAN does not have IP forwarding enabled.
ping x.x.x.235 from y.y.y.73
Ping(ICMP) x.x.x.235: 4 packets, 8 data bytes, interval 1 second(s).
16 bytes from x.x.x.235: icmp_seq=0 ttl=60 time=25 ms
16 bytes from x.x.x.235: icmp_seq=1 ttl=60 time=20 ms
sho tunnel "rtr-1_xxx"
Name Type Flags
rtr-1_xxx GRE x.x.x.132 => x.x.x.51 U
Total tunnels: 2