North American Network Operators Group
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Re: DSL Network Design Question

  • From: Robert E.Seastrom
  • Date: Sun Aug 14 10:58:58 2005 
"[email protected]" <[email protected]> writes:

> I am going to be cutting over about 75,000 DSL lines from
> one core network to another.  Does anyone have
> recommendations on subnet and DHCP scope size?  If I make
> them /23s I have to do about 145 subents.  If I make them
> /22s I only have to do about 73.  Being mainly an always on
> eyeball network I don't see any problems with making big
> subnets (/22).  

I'd say aggregate as much as possible based on what your LNS/RAS
equipment will handle in terms of actual customers.  In my OSPF, I
carry a /21 for each 7206VXR/NPE300 which may be a tad optimistic if
current P2P trends continue as they have - time to work some NPE-G1s
into my budget.  Of course, on the other end of the scale I carry /32s
for each static address customer, since that gives me maximum
flexibility for LNS shuffling in the future (to distribute load).

Peter Dambier is right that his ISP is avoiding .255 and .0.  Older MS
stacks (still plenty prevalent in the wild) get indigestion when
handed those final octets, notwithstanding the fact that they aren't
broadcast addresses on any network larger than a /24 or for one-ended
use like PPP...  if you don't exclude them you'll end up putting
additional load on your help desk.

The necessity to avoid .0 and .2555 results (on ciscos) in idioms such
as this:

ar01#sho run | inc ip local pool
ip local pool ar01-dynamic 223.126.80.1 223.126.80.254
ip local pool ar01-dynamic 223.126.81.1 223.126.81.254
ip local pool ar01-dynamic 223.126.82.1 223.126.82.254
ip local pool ar01-dynamic 223.126.83.1 223.126.83.254
ip local pool ar01-dynamic 223.126.84.1 223.126.84.254
ip local pool ar01-dynamic 223.126.85.1 223.126.85.254
ip local pool ar01-dynamic 223.126.86.1 223.126.86.254
ip local pool ar01-dynamic 223.126.87.1 223.126.87.254
ar01#


> <flameproof undies == on>
> suggestions, recommendations, advice?
>
> scott

Uh...  suggest/recommend/advise that you ought to use your full name
in posts and not an alias and first name, as required in the NANOG
Charter and AUP?  http://www.nanog.org/aup.html item 7.

Best,

                              ---Rob (member of the list-admin team)