On Thu, Aug 25, 2016 at 3:38 PM, Francis Kamau via skunkworks <skunkworks@lists.my.co.ke> wrote:

ISIS is preferred due to its simplicity, I know of two reasons;

1. ISIS does not use IPV4 address family - Even if your ISIS Address is wrong, it will still work. OSPF will complain in such a situation.

the default use of IS-IS is not IP based compared to OSPF which is IP based. That is no excuse for using wrong addressing, because if you do your MPLS, iBGP and eBGP won't work well either.

2. In a FLAT (Single Area) network ISIS can handle hundreds of routers while OSPF will struggle at 80-90 routers.

Ok this is a first. Do you mean 90 routers in your Area 0 or as a whole i.e. including other OSPF areas. If you understand how LSA's work, you will realize that a network that uses OSPF Areas does a better job of managing LSA's compared to a flat L1/L2 IS-IS.

If you are using OSPF as your IGP in an MPLS network, you can imagine the issues that might come up with the ABRs and ASBRs in a multi-area setup.

You need to clarify what you mean. Not all LSA's are sent across between the ABR's and the ASBR's. Plus there are many ways of optimizing LSA's on OSPF

Guys - please avoid mentioning multi-vendor - both are standard protocols.

They are both standards agreed. But you are forgetting one thing, vendors don't share a development team. So considering that there are two distinctively different group of people read one document and produce running code - their interpretation and implementation of the standard will have slight differences. Also for business reasons not all features may be supported at various release levels.

You perhaps need to experience this to better understand it.

Michuki.