IPv6 tunneling - gre ip

This example is going to use the same topology as IPv6 tunneling - IPv6IP. In this mode, the passenger protocol is IPv6, the carrier protocol is GRE and IPv4 is used as the transport.

Here is the network:

[R1]---[R2]---[R3]---[R4]

R1-R2: IPv6 network 2002:1:0:12::/64
R2-R3: IPv4 network 172.12.23.0/24
R3-R4: IPv6 network 2002:1:0:34::/64

Make sure you enable ipv6 unicast routing on R2 and R3:

R2(config)#ipv6 unicast-routing

R3(config)#ipv6 unicast-routing

Configuration is pretty much the same as ipv6ip except the mode is different. In fact, we don't even need to specify a mode as gre ip is the default. I will show it here just for clarity but note that it will probably not show up in the running-config:

R2(config)#int tunnel 1
R2(config-if)#description gre ip tunnel
R2(config-if)#ipv6 address 2002:2:0:23::2/64
R2(config-if)#tunnel source 172.12.23.2
R2(config-if)#tunnel destination 172.12.23.3
R2(config-if)#tunnel mode gre ip

R3(config)#int tunnel 1
R3(config-if)#description gre ip tunnel
R3(config-if)#ipv6 address 2002:2:0:23::3/64
R3(config-if)#tunnel source 172.12.23.3
R3(config-if)#tunnel destination 172.12.23.2
R3(config-if)#tunnel mode gre ip

Let's add the static routes:

R2(config)#ipv6 route 2002:1:0:34::/64 Tunnel1

R3(config)#ipv6 route 2002:1:0:12::/64 Tunnel1

Verify:

R1#ping 2002:1:0:34::4

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2002:1:0:34::4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 44/70/88 ms

R2#debug tunnel
Tunnel Interface debugging is on
R2#
*Mar 1 01:09:12.999: Tunnel1: GRE/IP encapsulated 172.12.23.2->172.12.23.3 (linktype=79, len=124)
*Mar 1 01:09:13.095: Tunnel1: GRE/IP to classify 172.12.23.3->172.12.23.2 (len=124 type=0x86DD ttl=254 tos=0x0)

Some of the benefits of this mode are that GRE tunnels can carry more than just IPv6. At work, we sometimes use them for multicast and some other non-IP traffic, we even use them to route normal IP packets to default destinations across VPN clouds.