In this post, we are going to cover one of the IPv4 to IPv6 transition mechanisms that we ran out of time for when we conducted an evening session of our CCIE R&S Lab Fundamentals Bootcamp course here at IPexpert. This feature is termed a GRE-IPv6 tunnel. It is a statically defined, point-to-point type of method for connected two network areas of IPv6 that might be separated by IPv4-only network devices.

In an earlier post we examined the Manual Configured Tunnel (MCT) for moving IPv6 traffic though IPv4 only networks. In this post, we are going to examine the Generic Routing Encapsulation (GRE) approach to tunneling IPv6 traffic through an IPv4 cloud.

With this approach, the IPv6 packet is encapsulated using a standard IPv4 GRE tunnel approach. Perhaps you are curious why we would add the overhead of GRE when we can encapsulate the packet for transport. Especially when you consider that we can encapsulate the packet directly as we did with the Manual Configured Tunnel (MCT).

The GRE approach is required within integrated IS-IS and IPv6 tunnel environments. If you plan on sending both IS-IS traffic and IPv6 traffic over the tunnel, the protocol field of the GRE header allows for the identification of the passenger protocol if you have both IS-IS and IPv6 traffic to send over this tunnel.

Here we demonstrate the configuration. Notice how similar this is to our MCT. Notice also that this would be the default tunnel encapsulation, we just show the commands here for illustration purposes.

ROUTERA

ROUTERA(config)# ipv6 unicast-routing

ROUTERA(config)# interface loopback 0

ROUTERA(config-if)# ipv6 rip MYRIPNG enable

ROUTERA(config-if)# exit

ROUTERA(config)# interface tunnel 0

ROUTERA(config-if)# ipv6 address 2001:1313::1/64

ROUTERA(config-if)# tunnel source fastethernet0/0

ROUTERA(config-if)# tunnel destination 10.20.20.3

ROUTERA(config-if)# tunnel mode gre ip

ROUTERA(config-if)# ipv6 rip MYRIPNG enable

ROUTERA(config-if)# end

ROUTERB

ROUTERB(config)# ipv6 unicast-routing

ROUTERB(config)# interface loopback 0

ROUTERB(config-if)# ipv6 rip MYRIPNG enable

ROUTERB(config-if)# exit

ROUTERB(config)# interface tunnel 0

ROUTERB(config-if)# ipv6 address 2001:1313::3/64

ROUTERB(config-if)# tunnel source fastethernet0/0

ROUTERB(config-if)# tunnel destination 10.10.10.1

ROUTERB(config-if)# tunnel mode gre ip

ROUTERB(config-if)# ipv6 rip MYRIPNG enable

ROUTERB(config-if)# end

Anthony Sequeira CCIE, CCSI

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