OSPF vs ISIS - Which do you prefer & why?

RT Parrish routetarget at gmail.com
Thu Nov 10 02:45:14 UTC 2016

I will definitely be looking up the notes from AOL that John referenced.
But working for a vendor and getting insight from multiple ISPs, here are a
few of the things that I hear most frequently:

1) Network Topology support - The differences between a single OSPF
backbone area and a contiguous set of Level-2 adjacencies will occasionally
be a deciding factor.
2) Feature Support on a per vendor basis - Some vendors will roll new
features out in one or the other protocols prior to the other.  Segment
Routing and some of its enhancements come to mind as being in ISIS first.
3) Layer 2 adjacencies - I think someone already mentioned that you form
adjacencies at layer 2 which also means that with a single adj you can
support multiple protocols (v4/v6). OSPF would require two different
instances to support both. Maybe good, maybe not. Depends on your desired
level of isolation between the two.
4) CPU performance is academic at this point - The SPF calculations in most
networks would require next to no difference between the two protocols even
if running both IPv4 and v6.

End of the day, use the right tool/vendor/technology for the right job.

Hope this helps,

On Wed, Nov 9, 2016 at 12:12 PM, Michael Bullut <main at kipsang.com> wrote:

> Greetings Team,
> ​While I haven't worked with IS-IS before but the only disadvantage I've
> encountered with OSPF is that it is resource intensive on the router it is
> running on which is why only one instance runs on any PE & P device on an
> ISP network. OSPF is pretty good in handling the core network routing while
> BGP & EGP handle the last-mile routing between PE & CE devices. BGP & EGP
> can run on top of OSPF. I came across this *article*
> <https://routingfreak.wordpress.com/2011/03/05/why-
> providers-still-prefer-is-is-over-ospf-when-designing-
> large-flat-topologies/>
> when
> scrolling the web a while back and I still want to find out if am the only
> one who thinks its a matter of choice between the two. Although there isn't
> distinct 1:1 argument, it's good we discuss it here and figure out why one
> prefer one over the other *(consider a huge flat network)**.* What say you
> ladies and gentlemen?
> Warm regards,
> Michael Bullut.
> ---
> *Cell:*
> *+254 723 393 114.**Skype Name:* *Michael Bullut.*
> *Twitter:*
> * @Kipsang <http://twitter.com/Kipsang/>*
> *Blog: http://www.kipsang.com/ <http://www.kipsang.com/>*
> *E-mail:* *main at kipsang.com <main at kipsang.com>*
> *---*

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