From: Chua, Parry (Parry.Chua@xxxxxxxxxx)
Date: Fri Jan 11 2002 - 11:51:26 GMT-3
Hi,
A picture print a 1000 word, we learn from variou sources, once we need
to verify to confirm some thing, do some tests with the condition, start
from simple to complex. You will learn a lot. I have done the tests for
eigrp, if you leave the auto-summary on (default), it will generate a
summary route to null 0 and this summary route will advertise to it
neig. The summary route is to drop those packets does not match the more
specify ropute and it has forward to this router. Summarization is to
reduce the routing information being send to
the neig.
Only if the route is externel and there is no internal network advertise
by eigrp, that route will not be summarize. So you have to be very
careful about the auto-summary, you can disable it and do manual
summarization.
Regards
Parry
-----Original Message-----
From: Frank B [mailto:frank@buff-net.com]
Sent: Friday, January 11, 2002 4:46 PM
To: 'Rajeev Siddappa'
Cc: 'ccielab'
Subject: RE: eigrp auto-summary and a null 0 route
I've seen the other responses and it seems we still haven't answered why
it didn't put a route to null 0 for both 20.0.0.0 and 168.71.0.0? I
can't seem to crack that nut but am very curious...perhaps we don't have
enough information? Any thoughts?
Also, Rajeev, 1 don't think I understand that you don't see a classful
boundary or what you mean by we're in the same router?? And I think
there's enough information given to show that but possibly not enough to
answer why there's only 1 null route installed.
We're given the network statement for the 20.0.0.0 network and the
routing table shows 20.1.1.0/24 is configured on loopback 0. I submit
this tells us this network will be advertised to EIGRP neighbors.
(barring any filtering and assuming we have neighbors...BTW we are
learning eigrp routes through s1 so we have at least 1 at ip address
168.71.9.1)
By inspecting the routing table it's clear we have 2 serial interfaces
connected within the 168.71.0.0 class B address space. We have s0 on
the 168.71.7.0/24 subnet and s1 on the 168.71.9.0/24 subnet. There's
also a network statement for 168.71.7.0 and 168.71.9.0 as well. The
router will advertise other subnets within 168.71.0.0 network out these
interfaces without summarization.
However, the router will summarize, advertise only the 20.0.0.0/8 vice
the 20.1.1.0/24 subnet, because when going out the s1 or s0 interfaces
we're crossing a classful boundary with with 20.0.0.0/8. I'm confident
this is correct and that we're certainly crossing classful boundaries in
the given scenario. But...I have been known to overlook a detail or two
from time-to-time. ;-)
Frank
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
CCIE Lab
Sent: Thursday, January 10, 2002 7:34 PM
To: j killion; Steven; ccielab
Subject: Re: eigrp auto-summary and a null 0 route
good, but why didn't it also create a summary route to
null for 168.71.0.0 subnets?
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Steven
Sent: Wednesday, January 09, 2002 8:51 PM
To: ccielab
Subject: eigrp auto-summary and a null 0 route
On one router which runs eigrp only ,the config and route table is as
follows,
sh run
...
router eigrp 1
network 20.0.0.0
network 168.71.7.0 0.0.0.255
network 168.71.9.0 0.0.0.255
no auto-summary
no eigrp log-neighbor-changes
...
168.71.0.0/24 is subnetted, 4 subnets
C 168.71.9.0 is directly connected, Serial1
C 168.71.7.0 is directly connected, Serial0
D 168.71.6.0 [90/20768000] via 168.71.9.1, 00:00:17, Serial1
D 168.71.5.0 [90/20384000] via 168.71.9.1, 00:00:17, Serial1
20.0.0.0/24 is subnetted, 1 subnets
C 20.1.1.0 is directly connected, Loopback0
after i add "auto-summary "command under router eigrp 1
the route table change to the following one ,
168.71.0.0/24 is subnetted, 4 subnets
C 168.71.9.0 is directly connected, Serial1
C 168.71.7.0 is directly connected, Serial0
D 168.71.6.0 [90/20768000] via 168.71.9.1, 00:00:03, Serial1
D 168.71.5.0 [90/20384000] via 168.71.9.1, 00:00:03, Serial1
20.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 20.0.0.0/8 is a summary, 00:00:01, Null0
C 20.1.1.0/24 is directly connected, Loopback0
i just want to know what "D 20.0.0.0/8 is a summary, 00:00:01,
Null0"
mean.Why is it added?
-----Original Message-----
From: Rajeev Siddappa [mailto:raj_lab@yahoo.com]
Sent: Thursday, January 10, 2002 9:36 PM
To: Frank B; 'CCIE Lab'
Cc: 'ccielab'; 'j killion'; 'Steven'
Subject: RE: eigrp auto-summary and a null 0 route
Frank, I understand.
Pls see below,
> > Auto-summarization only takes place when you cross
> > classful boundaries.
We are not crossing any classful boundaries here.
We are still in the same router.
> > You have 2 interfaces connected within the
> > 168.71.0.0 space; so it sends
> > advertisements out those interfaces for subnets
> > within 168.71.0.0
> >
> > However, other networks advertised out those
> > interfaces are summarized
> > on their classful boundary. Hope this helps.
> >
> > Frank
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