[c-nsp] Route Reflector Design

[Jeff Aitken]

On Wed, Jul 02, 2008 at 11:34:42AM -0400, Mike Johnson wrote:
> How am I able to utilize thousands of devices in a flat IGP domain? I
> thought only a couple hundred is recommended before deploying multiple
> areas.

There is no one right answer.  It depends on your network: what is the
topology, how much aggregation are you doing, how stable are the devices
and links, etc.  As usual, apply the KISS principle.  If you don't NEED
multiple areas, don't use them.  

That said, *thousands* of devices likely means multiple areas.


> Are you guys recommneding OSPF or ISIS?

Quoting from Dave Katz' excellent presentation from NANOG19 [1]:

    "For all but extreme cases (large full-mesh networks), protocols are
     pretty much equivalent in scalability and functionality

     Stability and scalability are largely artifacts of implementation, not
     protocol design

     Familiarity and comfort in both engineering and operations is probably
     the biggest factor in choosing"

I've worked for at least two providers that switched from OSPF to ISIS,
and my current employer uses both in various places.  I'd recommend using
what your ops folks are familiar with; the cost of learning something new
will likely outweigh any (largely theoretical) gain.

One final consideration is that OSPF support is pretty ubiquitous across a
wide variety of devices (routers, switches, firewalls, load balancers, etc)
while ISIS support tends to exist only in routers (and to a lesser degree,
switches) used by service providers.  Whether this matters to you depends
on your current & expected vendor/platform set.


--Jeff

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