xxvaf@WR.BBNPLANET.COM (Vince Fuller) writes:

There are some drawbacks to IS-IS: ...

IS-IS uses an underlying traffic exchange which is based on OSI/CLNS. This introduces requirements for OSI addressing and CLNS implementation which are otherwise useless in an IP-centric network. IMHO, this represents a substantial bit of operational complexity (obtaining CLNS addresses, teaching operations/engineering staff how to use them and interpret them while debugging, etc., etc...)

While it does require OSI addressing, it does not require CLNP forwarding. As to the engineering and operations aspects, the additional complexity can, with a reasonable implementation, be almost completely hidden. For example:

show isis adjacency IS-IS adjacency database: Interface System L State Hold (secs) SNPA fxp0.0 lab5 2 Up 16 0:0:c0:cc:a0:bf fxp0.0 lab2 2 Up 25 0:0:c0:e8:69:db fxp0.0 lab10 1 Up 22 0:a0:c9:36:b3:a6

On a pragmatic note, though, the relative successes of IS-IS and OSPF in the large provider marketplace probably has more to do with the relative competence of the cisco's original OSPF and IS-IS implementors than anything else (only someone else who suffered through OSPF's growing pains way back in the 9.0-9.1 days can really appreciate this comment...)

Very true, tho those of us who had ringside seats do sympathize. ;-) Tony