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SubjectRE: howto disable auto route setup?
Date
>> The idea of class A->C networks has come and gone because of the
>> lack of suitable continuous addresses defined by the original
>> standard. It is now common to make large networks using contiguous
>> small networks. The netmask is the thing that defines the "network".
>> Stuff that doesn't fit through the mask is sent/received through
>> the "default" route. Once this is understood, configuring a network
>> is simple.
>
>I don't remember the RFC that says this either. Try to configure a Bay
>router with a subnet mask less than the class of network for the IP. Can't
>do it. I'd try on a cisco router, but I don't have one available at the
>moment. I doubt it would let you setup an >interface< with an illegal
>netmask either. If it does, then it's a bug.

Well, aside that RFC's are comment requests and not standards...
They become accepted or not as time goes by -- they also become
obsolete.

CISCO does support CIDR routing, you just need to turn on the
classless option -- by default they fall back on old habits. And
I know from a friend of mine that bay routers can be made to do
classless routing in recent days.

Also, most ISP's and such do classless routing. Some places only
need an a.b.c.d/28 or some such for their small network, and with
IP addresses having become such a commodity it was only prudent.
This goes ditto for those places that have a firewall/proxy and all
their internal address are in the 192.168.0.0/16, since they now
need P-t-P routing on an interface between them and a provider, everything
else on the class subnet goes default or somewhere else. I could
repeat myself for VLANs.

The short of it is, is that CIDR routing is pretty much the accepted
way of doing networking these days (note, that stands for Classless Internet
Domain Routing, which implies that paying attention to classes while doing
CIDR routing makes very little sense). The classful stuff is tending
to be supported mostly because of the necessity of supporting old networks
and methods.

Eric Kasten
kasten@nscl.msu.edu

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