IGPs in use

Mon Oct 12 23:47:12 UTC 1998

> it probably depends on what you mean by "large".  If you mean "the 5 largest"
> then yes, most use ISIS (but not all).  If you mean the 50 largest, then 
> OSPF becomes much more prominent (that is, hardly anyone but the largest
> ISPs use ISIS, at least from my discussions with dozens at my previous
> and current employer).

Likely because their networks have been 'round the longest and ISIS was the 
"IGP of choice" not long ago.  Also, some have/had requirements for ISO CLNS 
ISIS routing support as well.

The use of ISIS shouldn't lead folks to believe that OSPF doesn't scale well 
though.

-danny