12 Oct
1998
12 Oct
'98
7:47 p.m.
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