IPv6 tunneling over IPv4 - Manual Tunnel

We know that IPv4 and IPv6 addresses are not compatible with each other. Let's say the existing infrastructure is running on IPv4. If we need to implement IPv6 on few of the hosts, we need to use some sort of a technique for IPv6 hosts to communicate with each other using existing IPv4 network. One of the ways we can achieve this is by using a tunneling method.

In this post we will see how we can implement "Manual Tunnel". 

As shown in the diagram below, we have R1, R2 and R3 connected with each other. 

All three routers are running EIGRP and there is an IPv4 reachability from R1 to R3.

BFD (Bidirectional Forwarding Detection)

In this post, we will look into a feature called BFD (bidirectional forwarding detection). In normal routing protocol operation, the link failure is detected by using the hello/holddown/dead timers. 

Depending on the routing protocol, you can lower the timers to achieve fast failure detection. e.g. in the case of OSPF the lowest dead time can be one second and one can set the hello interval as low as 50ms.

However lowering these timers can result in higher CPU utilization. Also it will unnecessarily waste the link bandwidth. 

There is a better way of achieving fast failure detection through BFD. BFD is a UDP-based protocol that provides fast (in milliseconds) routing protocol independent detection of layer-3 next hop failures.

Let's see how it works. As shown in the diagram below, routers R1 and R2 are connected via Switch 1 and Switch 2. Both the routers are running OSPF and we can see the OSPF neighbourship is up.