A short look at the GRE (Generic Routing Encapsulation) and how we can configure an OSPFv3 neighbor relationship across it.
In this scenario, we will establish a GRE tunnel between R9 and R14:
We will use the tunnel to send IPv6 packets across the intermediate IPv4 network and we will establish an OSPFv3 neighbor relationship between R9 and R14.
The tunnel between R9 and R14 will be established between their loopback IP addresses. Traffic send into the tunnel from R14's perspective will be as follows:
Let's go ahead and configure the R14 side of the tunnel:
This (on both ends) is enough to establish a tunnel through which we can send IPv6 packets. The IPv6 address that was configured on the tunnel will be installed into the routing table as a direct route.
Let's verify whether or not we can ping across the tunnel:
We can ping the IPv6 address across the IPv4 network.
In a traceroute, the 2001:2::9 is only one hop away. The IPv4 packets carrying the tunneled traffic travel two hops in our example.
Now , let's establish a neighbor relationship between R14 and R9 across the tunnel. We'll use BFD to shorten the time needed to detect the neighbor being down:
After configuring R9, let's check out the neighbor relationships:
That's about it. Besides BFD, there is also the possibility to use ethernet oam to keep track of the GRE tunnel status.