From: Mike Gutknecht (mike@xxxxxxxxxxxxx)
Date: Tue Jun 12 2001 - 20:23:02 GMT-3
I think of the "network" commands in the router config mode as enabling
interfaces for routing. Those interfaces that fall within the network range
specified are activated for routing. For IGRP, RIP, and EIGRP, the range is
the implicit classful range.
For a weird yet instructive example,
int e0
ip addr 10.1.1.1 255.255.255.0
int e1
ip addr 10.2.2.2 255.255.255.192
int e2
ip addr 10.3.3.3 255.255.255.224
router igrp 1
netw 10.0.0.0 -> Enables interfaces that represent networks within
10.0.0.0-10.255.255.255
In this case, all three interfaces fall under the 10.0.0.0/8 network space
so they are all enabled for IGRP. Now, IGRP will only send /24's out e0,
/26's out e1 and /27's out e2. Also, because there is no mask information
in recieved packets, it will assume that received routes on e0 are /24s,
recieved routes on e1 are /26's, and received routes on e2 are /27's.
Now, when you do what Carolyn did
int e0
ip addr 192.168.33.1 255.255.224.0
router igrp 1
netw 192.168.33.0
the network associated with e0 is not entirely within the range specified by
the network statement and thus is not activated. (I tested and got
Carolyn's result as well.)
Oddly, this behavior is different for OSPF where you are matching the
interface's configured IP address rather than the network that the interface
represents.
-Mike G
-----Original Message-----
From: Rick Stephens [mailto:rstephens@wantec.com]
Sent: Tuesday, June 12, 2001 10:32 AM
To: 'GroupStudy'
Cc: 'Carolyn Camarda'
Subject: RE: IP Addressing & IGRP Question
IGRP does not support VLSM, but it does support FLSM. All subnet masks must
be of a fixed length. Since RIPv1 and IGRP routing updates do not include
subnet mask information, a router will assume that the subnet mask with
which it has configured on all its interfaces is the same for all subnets. A
single mask must be used for all subnets of a given classful network.
Different masks can be used for different classful network addresses.
(Caslow p.300)
I think Carolyn said that she tried with a /19 and it didn't work, but tried
it again with a /30 and it did work. The question then would be is does IGRP
support supernets (shorter then the classful boundry). Louie confirmed in
his lab that a /19 can be used.
Confirm 'ip classless'
Maybe also look for a loopback address that is a different subnetmask? They
all need to be the same.
Just my $.02
-----Original Message-----
From: ElleJf(Yahoo) [mailto:ellejf@yahoo.com]
Sent: Tuesday, June 12, 2001 9:43 AM
To: louie kouncar
Cc: 'GroupStudy'; 'Carolyn Camarda'
Subject: RE: IP Addressing & IGRP Question
I would be surprised if /19 mask can work. IGRP does not support VLSM, so
that you can use 192.168.33.0/19 which is a classless subnet. This ip
address belong to class C, so the mask should be /24. In IGRP routing
update packets, only 192.168.33.0 will be recorded (In fact, 192.168.33, 3
octets.) There is no info that you can know what the mask will be.
The only way it would work is that router use locally configured subnet mask
on interface, in this example, /19 as mask. But it doesn't make sense. Can
you provide your config and network diagram?
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of louie
kouncar
Sent: Tuesday, June 12, 2001 1:18 PM
To: 'Carolyn Camarda'; 'GroupStudy'
Subject: RE: IP Addressing & IGRP Question
Well,
I just did a test to see if this is an issue, everything worked just
fine using 192.168.33.1/19 on R1 and 192.168.33.2/19 on R2....
Please post your full configs so I can look for issues....
Thanks
Louie Kouncar
UUNET
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Carolyn Camarda
Sent: Monday, June 11, 2001 11:21 PM
To: GroupStudy
Subject: IP Addressing & IGRP Question
I'm having a mental block with some IGRP configuration, I would
appreciate a
little nudge. I have my router e0 interface set up with the IP address
of
192.168.33.1/19. I have an IGRP network statement of 192.168.33.0.
With
this I do not get IGRP to start up on the E0 interface. I tried the
network
statement of 192.168.32.0 thinking that it may be wanting the VLSM
network
address. None the less I can not get IGRP to fire up.
If I use a class a (10.) or class b (172.16.) address with the /19
mask, I
don't have a problem. When I change the 192 IP address on e0 to a
longer
mask, such as /30 it works fine. My code version is 12.0.5T. I have ip
classless defined on the 2500 router
Is there something with regards to IGRP when the mask can't be shorter
than
the classful boundary to which the address belongs. Or what am I doing
wrong?
Any help would be appreciated.
Carolyn
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