The options available for an IGP routing protocol within 6NET were: static routing, RIPv6 or IS-IS. The option ‘static routing’ would have been very difficult to manage in practice, and would not have been very scalable. The dynamic routing options available were ‘RIPv6’ and ‘IS-IS’.

RIPv6 is a distance vector routing protocol while ‘IS-IS’ is a link-state protocol. Although a distance vector routing protocol is easier to troubleshoot and the operation simpler to understand, it was preferred to utilise a link-state protocol due to its advantages in convergence, tuning and additional features (like opaque information, enhanced TLV (Type/Length, Value) information for Traffic
Engineering, etc.).

Integrated IS-IS was used only to distribute the core router reachability. For everything else BGP4+ was used. No route exchange was used between IGP and EGP.

The 6NET ISIS topology is depicted in Figure 12-2.