IPv6: IS-IS or OSPFv3

Kevin Oberman oberman at es.net
Sat Dec 27 04:37:41 UTC 2008

> Date: Fri, 26 Dec 2008 19:47:21 -0700
> From: "devang patel" <devangnp at gmail.com>
> Hello,
> I do have some confusion about which one is better for IPv6 in Service
> Provider networks as far as IP routing and MPLS application is concern!
> 1. Which protocol should i use to support the IPv6 in network: ISIS or
> OSPFv3?
>     As ISIS has multi-topology feature that can give us capability to run
> IPv4 network separate from IPv6 right! and same thing with OSPF: OSPFv2 will
> be used for IPv4 routing and OSPFv3 will be used for IPv6 routing! again Its
> look like resource    utilization for both the protocol will be same as they
> are going to use separate database for storing the routing or topology
> information. ISIS still has advantage over OSPF as it does use the TLV
> structure which can help in expanding network to support the new feature!
> 2. MPLS is not distributing label for IPv6 protocol so again there will not
> be any IGP best path calcuated for any MPLS related application for IPv6!
> 3. what if i have already running OSPFv2 for IPv4 in the network then should
> i think for migrating to ISIS?
>    if yes then what are the advantages that I can look at for migrating my
> network to IS-IS?

FWIW, we run OSPF for IPv4 and ISIS for IPv6. We started with ISIS for
v6 because we were routing IPv6 before OSPFv3 was available. 

The main reason I prefer ISIS is that it uses CLNS packets for
communications and we don't route CLNS. (I don't think ANYONE is routing
CLNS today.) That makes it pretty secure.

I would hope you have a backbone well enough secured that you don't need
to rely on this, but it does make me a bit more relaxed and makes me
wish we were using ISIS for IPv4, as well. The time and disruption
involved in converting is something that will keep us running OSPF for
IPv4 for a long time, though. I remember the 'fun' of converting from
IGRP to OSPF about 13 years ago and I'd prefer to retire before a

The real issue is that you need to run something you understand and can
manage effectively. It that is OSPF, it will certainly do the job. If it
is ISIS, it will, too. The real differences are few and not significant for
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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