The MPLS-OPS Archive

[Mark Lewis <markl11_uk@yahoo.co.uk>]

Just to add a few useful references on IS-IS/OSPF:

1. A slightly old, but still good comparative from
Dave Katz:

http://www.nanog.org/mtg-0006/katz.html

2. A good OSPF/IS-IS comparison can be found in 'IS-IS
Network Design Solutions' (Cisco Press).

3. Cisco support for Multi-topology IS-IS (M-ISIS)
(specifically support for IPv6):

http://www.cisco.com/en/US/tech/tk872/tk373/technologies_white_paper09186a00801e199f.shtml

M-ISIS also allows support for a (seperate) multicast
topology. With this you can implement inconguent
topologies (unicast/mulitcast) *within* an autonomous
system. I know that Juniper currently supports this,
but I believe I'm right in saying that Cisco doesn't
currently support this - not sure if its really that
useful, though (be interested to hear if anybody has
actually implemented this).

4. More on IS-IS support for IPv6 see (do a search on
google, or see the IS-IS for IP Internets (isis)
working group at www.ietf.org):

draft-ietf-isis-ipv6

Mark


 --- Eric Osborne <eosborne@cisco.com> wrote: > On
Fri, Jan 23, 2004 at 07:31:49AM -0000, Sunil
> Menon K wrote:
> > Hi all
> > I work for a large ISP which currently has OSPF
> for IGP,running MPLS
> > VPN and are headed for implementing QOS and
> Traffic Engineering and
> > moving towards migrating to IPV6 and becoming a
> Tier 1 ISP.Since
> > most Tier 1 ISPs are running IS IS as their IGP,I
> have been working
> > on looking at IS IS in relation to OSPF to deciede
> if IS IS holds
> > any significant advantages keeping mind two key
> aspects of
> > convergence,scalability and support as the network
> grows.I have a
> > few questions with regards to the same.
> 
> The difference between ISIS and OSPF is a lot like
> the difference
> between SONET and SDH, but see inline
> 
> > 1.Does IS IS have the flexibility of supporting
> both v4 and V6 
> > implementations?Is the same available with OSPFv2
> aswell?
> 
> I'm not sure what development/standards are at; I
> know there's OSPFv3,
> and ISIS should, if anything, be simpler to
> implement.
> 
> > 2.Does IS IS hold an edge over OSPF in anyway for
> Traffic 
> > Engineering implementations?
> 
> There are some features that tend to ship for ISIS
> first and OSPF in
> the next release, but if you aren't concerned with
> bleeding-edge, then
> no.
> 
> 
> > 3.With regards to the basic routing functionality
> ....can it be
> >    safely said of IS IS as being more scalable
> with its support for
> >    larger areas and a more strict hierarchy model?
> 
> Sure!  You can also say that the moon is made of
> cheese, up is down,
> and bad is good..:)  
> 
> The persistent rumors of OSPF being less scalable
> are long due for
> demise.  It's not true.  It used to be true, maybe
> 10 years ago, but
> it's not any more.  They're largely identical in
> this respect.  
> 
> I'm not sure what 'a more strict hierarchy model'
> is.  Personally, I
> never liked the l1->l2 automatic default stuff, but
> that's just me.
> 
> 
> > 4.What in your opinion are the key benefits would
> a Tier 1 ISP stand to
> > derieve from IS IS implementation of the two level
> hierarchial Link 
> > state protocol.
> 
> The same ones as they'd get from an OSPF
> implementation of same...:)
> 
> 
> 
> eric
> 
> > 
> > Any inputs and guidance on the same would be
> highly appriciated.
> > 
> > Thanks and Regards,
> > Sunil.
> > 
> > 
> 
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