8. IGP Issues

As stated above, many router vendors require an identifier for tagging their IGP processes. However, this tag does not need to be globally unique. In practice this information is never seen by exterior routing protocols. If already running an exterior routing protocol, it is perfectly reasonable to use your AS number as an IGP tag; if you do not, choosing from the private use range is also acceptable (see "Reserved AS Numbers"). Merely running an IGP is not grounds for registration of an AS number.

With the advent of BGP4 it becomes necessary to use an IGP that can carry classless routes. Examples include OSPF [OSPF] and ISIS [ISIS].