OSPF vs ISIS - Which do you prefer & why?

Joel M Snyder Joel.Snyder at Opus1.com
Thu Nov 10 12:30:24 UTC 2016

 >> Vendor support for IS-IS is quite limited - many options for OSPF.

 >Depends on the vendor.

I think you misunderstood his point: it's not the knobs, but the 
vendors.  Generally, when you're trying to integrate random crap into an 
otherwise well-structured network, you'll find OSPF available, but very 
rarely IS-IS.

I run into this a lot in the security appliance space, where you want 
your security appliances to either learn or advertise routes internally 
(VPN tunnel reachability is a big reason for this), but also in devices 
such as load balancers and other middlebox cruft that occasionally needs 
to participate in routing advertisement/subscription.

Some vendors grab random open source routing protocol code that includes 
everything and dump it into their boxes, usually accessible via an 
entirely separate configuration interface; this can include IS-IS, but 
these implementations rarely actually work as they are usually "check 
list" implemented for a specific RFP or customer and never get widely 

The ones who actually care about making it work almost always include 
RIP and OSPF, with a few shout-outs to BGP.  IS-IS (and OSPF v3) rarely 
makes the cut.

In a world where you are doing well-controlled Cisco/Juniper/etc 
networks with fairly homogeneous code bases, the engineers get to have 
this discussion.  When you have to link in devices for which routing is 
not their primary reason to exist, your options narrow very quickly. 
It's not ideal; that's just the way it is.


Joel M Snyder, 1404 East Lind Road, Tucson, AZ, 85719
Senior Partner, Opus One       Phone: +1 520 324 0494
jms at Opus1.COM                http://www.opus1.com/jms

More information about the NANOG mailing list