It is possible to exchange routing information between two autonomous systems or routing domains without using a standard exterior routing protocol between two separate, standard interior routing protocols. The most common way of doing this is to run both interior protocols independently in one of the border routers with an exchange of route information between the two processes.
As with the exchange of information from an EGP to an IGP, without appropriate controls these exchanges of routing information between two IGPs in a single router are subject to creation of routing loops.