-----Original Message-----
From: Burnham, Chris
Sent: 26 July 2001 12:14
To: 'suleman ibrahim aboo'
Subject: RE: classless routing [7:13847]
It will take the default route for the following reason:
first of all I assume that you are running a classfull protocol such as RIP
or IGRP.
When running a classfull protocol & subnetting a major class network as
below( 10.6.0.0 is a subnet of 10.0.0.0) etc, the contigous rule states that
all subnets will be using the same mask and must be contigous, therefor the
router assumes that it knows about all subnets.
When the packet arrives for 10.7.0.0/16 it will do a classfull lookup on the
subnet information it know's about ie. the first two octets, it will not
find a route and drop the packet. For a classfull protocol with no ip
classless the default route will only be used for different major class
networks eg. a packet for 11.7.0.1 would hit the default route.
however this changes when ip classless is turned on ( on by default).IP
classless will over ride the contigous rule and make the router look for the
longest match. Therefor in answer to you question the packet for 10.7.0.0/16
will hit the default route when IP classless is on but will be dropped if no
ip classless is configured.
NB. This is easily tested if you have two routers available.
I hope this helps Chris.B
-----Original Message-----
From: suleman ibrahim aboo [mailto:[EMAIL PROTECTED]]
Sent: 26 July 2001 09:57
To: [EMAIL PROTECTED]
Subject: classless routing [7:13847]
Can you please explain what would happen and why.
A router has ip classless enabled. It's routing table has entries for
10.5.0.0/16 and 10.6.0.0/16 and a default route 0.0.0.0. A packet arrives
for a destination on 10.7.0.0/16. Which route does it take ?
thanks in advance
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