Talk:Constrained Shortest Path First

Present in OSPF and IS-IS
The article's focus is on MPLS, but link pruning exists in both OSPF and IS-IS. In either of these protocols, unidirectional links are removed before shortest path computation. I.e., if router A's LSA/LSP advertises a link to router B, but router B's LSA/LSP does not advertise an opposite link, then the supposed link from A to B is pruned. IS-IS performs an additional pruning of all outbound links from routers which have the overload (OL) bit set in their LSP (except for self, i.e. if it's the calculating router's own LSP). (This can be – inaccurately – emulated in OSPF by setting the metrics of these links much higher than those of "normal" links.)

What the IGPs do not do is pruning different sets of links on the same router, that is, have a single router calculate multiple routing tables. I am guessing this is the distinguishing criterion for calling it CSPF. In any case, this point could be clarified, if anyone knows how. Aragorn2 (talk) 13:31, 26 October 2015 (UTC)