[c-nsp] VLSM

[Mark Persiko]

If you have a hierarchical network topology with the gateway of last
resort facing  one egress point at the core, then I've noticed that "ip
classless" has the unfortunate side effect of sending all traffic out
that egress pipe, whose destination is for subnets that aren't used
within the network.  That is my condition right now and I am burning
bandwidth, and seeking a solution!

In other words, if you are using 172.16.1/24 and 172.16.2/24, and you
have packets headed for 172.16.3/24, "ip classless" will make them head
to the gateway of last resort instead of just dropping them.

I am using EIGRP in my network.  I have it in mind to turn off "ip
classless."   This is one advantage of "classful routing;" traffic bound
for any non-defined subnets are dropped.  However, in my network, I have
other subnets of 172.16 that are beyond the EIGRP cloud, so I need to be
able to get to them.

One solution I've considered is explicit static routing for all valid
subnets of 172.16 and then null routing anything else for 172.16/16
itself.  What do you think?

Thanks,
 Mark P.

- Mark C. Persiko, Network Engineer
- IT Division, Boulder Valley School District


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Brant I. Stevens
Sent: Monday, January 10, 2005 9:26 PM
To: lists at hojmark.org; 'matthew zeier'; 'Gert Doering'; 'Shaun'
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] VLSM

While I agree that having no class (when talking about networking :B) is
a
good thing, "classfulness" is not completely dead...  Sometimes you
still
have to use RIP v1..  There's also EIGRP and BGP auto-summary using
classful
boundaries.


On 01/10/2005 06:59 PM, "lists at hojmark.org" <lists at hojmark.org> wrote:

>> However, I can't get people (sales) to stop calling it "class c".
> 
> Even worse is when they (and some 'techs') call everything /24 a
"class C"
> and a every /16 a "class B", even when it's 10.10.10/24 and 10.10/16,
for
> example.
> 
> Yuck.
> 
> -A
> 
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