[nsp] /30 over WAN links

Church, Chuck cchurch at wamnetgov.com
Fri Feb 6 17:40:35 EST 2004

One advantage of using a single block for a customer (and forcing them
to use ip unnumbered on an interface) is that you end up with just one
subnet associated with that customer, rather than two.  End result is
less routing table entries on your end.  It's not a replacement for
thoughtful summarization, but it can't hurt.

Chuck Church
Wam!Net Government Services
13665 Dulles Technology Dr. Ste 250
Herndon, VA 20171
Office: 703-480-2569
Cell: 703-819-3495
cchurch at wamnetgov.com
PGP key:

-----Original Message-----
From: Steve Lim [mailto:limmer at execpc.com] 
Sent: Friday, February 06, 2004 10:33 AM
To: cisco-nsp at puck.nether.net
Subject: [nsp] /30 over WAN links

Hello all,

	It has been an age old policy at my company to place a /30 over
the WAN 
links ever since who knows when, and I've never really questioned it. 
But now, we've merged with another company, and they do not follow such 
a policy at the Access Layer. In fact, they use a /29 (or shorter 
prefixes, if customer requires more IPs) over the WAN links, and  use 
the IPs not already used by the respective end interfaces for 
hosts/devices on the remote/customer end.

	I had assumed that most, if not all companies use /30s. So this
came as 
a surprise. But more importantly, I can't come up with a good reason why

we use /30s either.

My questions:

1. At the Access Layer, what are the benefits of using /30s, over 
subnets with shorter prefixes.

2. Are there administrative benefits to such a policy?

3. Are there routing or switching benefits to such a policy?

4. Is it a best practice policy?

Thank you for comments.

Steve Lim - Network Engineer (Michigan)
Corecomm -An ATX Communications Company
Support Bacteria, it's the only culture
everyone has in common. -limmer

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