OSPF vs ISIS - Which do you prefer & why?

I'm not sure it is worthy of an argument. I think I've only ever heard
of anyone migrating from one to the other. That was AOL presenting
their conversion from OSPF to IS-IS at NANOG a number of years ago:


The article you refer to more or less covers some of the major
differences, largely academic these days. They are close enough
alike now that it is probably just best to use what you know or already
have running.

When I migrated a RIPv2 network to OSPF I don't remember if I
consciously choose it over IS-IS for any particular reason or, more
likely, just went with it because it seemed like the IETF-preferred way
to go. That would have been a dumb reason and later I kind of wish I
had used IS-IS, because of the security isolation at layer 2 and
relatively modest changes to support IPv6. But I wouldn't go through
the trouble of changing it now. There is no compelling reason.

I've considered leaving IPv4 on OSPF and putting IPv6 on IS-IS, but I'm
not sure it really matters. It might be nice to get the experience on
the resume, but that might not be a good justification to the network
staff and management for a production network.


When I converted an OSPF network at $old_job to IS-IS back in 2011, the
NOC were not too pleased with the idea.

Took several workshops to reassure them that we didn't all need to move
to Mars if we did this. Suffice it to say, the migration went famously,
and considering it works well, they didn't even need to touch it at all
on an ongoing basis (not that OSPF needed hand-holding).

The resistance to move is mostly borne out of fear (and a bit of
laziness to learning something new). That can be said for pretty much
anything the network has never ran before that Engineering want to
implement. Giving them leadership does the trick.