From: Lachlan Kidd (lkidd@xxxxxxxxxxxxxxxxxxx)
Date: Mon Apr 16 2001 - 02:20:49 GMT-3
Hi Darren,
Can you send a picture with adressing of links etc.
What you are saying is correct. IGRP sends the following type of routes
a) classfull routes if the network being advertised is not configured on the
advertising router.
b) networks that match the mask of the advertising interface if the route
and interface belong in the same classfull network.
My inital guess is you've got
'no ip subnet-zero'
on the router rx'ing the routes (or a version of IOS where this is
default).
I've just done some tests on this and found the following
R3-----R1
R1 has got a a number of interfaces from the 1.0.0.0 network, all with
varying masks. The link betwen R1 and R3 is 1.3.1.2/30. Both are running
IGRP. R1 has a loopback (1.5.1.0/30) also subnetted to /30 and that route
appears in R3's table. Cool.
Now...it gets a little strange...
I configured 'no ip subnet-zero' on R3, and a loopback on R1 with an address
of 1.0.0.0/30.
R3 gets the update with both routes (according to debug), but only the
original 1.5.1.0/30 route is put into the table. That's still fine.
Put 'ip subnet-zero' onto r3 and both /30 routes appear. Again, as expected.
Finally...re-applied 'no ip subnet-zero' to R3. Both routes still in table.
I would have expected that the 1.0.0.0/30 route would have been aged
out..but next update it got refreshed.
When I clear ip route * the route goes away and does not come back, but once
it made it into the table, IGRP kept on updating it. Weird
Anyone with any comments.
Lachlan
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Darren Ward
Sent: Monday, 16 April 2001 2:20:PM
To: ccielab@groupstudy.com
Subject: IGRP Question
Hi Guys,
A simple one I'm sure but I don't know the answer without default or
static routes etc....
Consider a network using 172.16.0.0/16 split into all /24's
172.16.0.0/24 and 172.16.1.0/24 are configured on interfaces on an edge
router and the
command 'redistribute connected metric blah blah' is in the IGRP
process.
Now on the remote IGRP routers all i see is 172.16.1.0/24 i do not see
172.16.0.0
Is this because IGRP assumes any route for 172.16.0.0 is the classful
/16 route since there is no subnet mask info in IGRP and ignores it
because it does not match the /24 mask required?
Bit confused about this one as I thought as long as i used a /24 mask on
172.16.0.0 it should still redistribute.
What's a workaround for this?
Darren
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