[afnog] afnog Digest, Vol 54, Issue 23

[Peter Nyamukusa]

Hi Mark,

I migrated to ISIS from OSPF before deploying MPLS after taking some of the
considerations below:

    *  IS-IS does not use level 3 routers.
    * Some routers, called L1/L2 routers, belong to both area types.
    * Unlike OSPF, IS-IS routers are not required to be connected to a
contiguous backbone area. In fact, the backbone area can also be segmented
in IS-IS.
    * IS-IS uses the concepts of router levels, which is similar to OSPF
areas. L2 routers are similar to OSPF backbone routers, and L1/L2 routers
are analogous to OSPF ABRs.
    * With IS-IS, there is no restriction that all backbone routers (level 2
routers) be contiguous
      such as the backbone area of OSPF.
    * In OSPF all areas must be directly linked to area 0, and the backbone
area must also not be segmented.
    * With IS-IS, the backbone area can be more easily extended since all L2
routers need not be linked directly together.
    * With regard to CPU use and the processing of routing updates, IS-IS is
more efficient
      than OSPF.
    * In IS-IS, one LSP is sent per IS-IS router in each area (including
redistributed prefixes [routes]), compared to the many OSPF LSAs that would
be sent.
    * Not only are there fewer LSPs to process, but the mechanism by which
IS-IS installs and withdraws prefixes is less processor intensive.
    * In IS-IS, the entire SPF table is not refreshed periodically like
OSPF, which does so every 30 minutes by default.

Try to design your network so it can run in a single area/level which
makes things like TE/FRR or fast convergence easier later..
but again the choice is up to you

Cheers 
Peter

-----Original Message-----
From: afnog-bounces at afnog.org [mailto:afnog-bounces at afnog.org] On Behalf Of
Mark Tinka
Sent: Wednesday, September 24, 2008 12:34 PM
To: Frank A. Kuse
Cc: afnog at afnog.org
Subject: Re: [afnog] afnog Digest, Vol 54, Issue 23

On Wednesday 24 September 2008 17:18:29 Frank A. Kuse wrote:

> For now we have reverted all interfaces to be similar but we know that 
> based on what Mark and Peter sent, if we change MTU on the gigabit 
> interface to 1500, mpls works fine.

Just curious, were you running IS-IS as your network's IGP before you
decided to setup MPLS, or did you setup IS-IS with the sole purpose of
running MPLS?

Cheers,

Mark.