From: Ouellette, Tim (tim.ouellette@eds.com)
Date: Tue Dec 31 2002 - 01:42:58 GMT-3
Playing around with AD's/Summaries/Null0 filtering for EIGRP. Let me know
if you have any ideas.....
9.9.9.0/24 ---R9-----192.168.1.0/24----R7----ethernet---r6
Router 9 is advertising 9.9.9.0/24 to r7. It arrives there as a /24. On
router7 i've configured
a "ip summary-address eigrp 1 9.0.0.0 255.0.0.0 5" to make r7 adveritse the
9.0.0.0/8 out of
it's ethernet interface and it shows up in the routing table as such. When I
add the summary
onto ethernet2, the 9.0.0.0/8 gets advertised out ethernet2 but not
9.9.9.0/24 (sounds right)
see the following...
18:34:46: IP-EIGRP: 9.9.9.0/24 - don't advertise out Ethernet2
18:34:46: IP-EIGRP: 9.0.0.0/8 - do advertise out Ethernet2
r7#r
9.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 9.9.9.0/24 [90/2297856] via 192.168.1.1, 00:00:04, Serial3
D 9.0.0.0/8 is a summary, 00:00:41, Null0
C 192.168.1.0/24 is directly connected, Serial3
C 192.168.2.0/24 is directly connected, Ethernet2
If I use the "ip summary-address eigrp 1" with a 255 AD, the 9.9.9.0/24
route shows up
in r7, but it doesn't advertise the /24 or the summary of /8 (because of the
255 AD) and
I see the following message on r7
18:31:47: IP-EIGRP: 9.9.9.0/24 - don't advertise out Ethernet2
18:31:47: IP-EIGRP: 9.0.0.0/8 - not in IP routing table
So, it's trying to function like normal and create the summary and suppress
the more specific
but because I said the AD of the summary was 255, it doesn't make it into
the routing table
but the more specific is supressed as if it's there (odd, but okay,
understandable)
Now, what I was trying to do besides just putting the AD on the
summary-address was to use the
"distance" command under the eigrp process to get the Null0 route out of the
table. I figured
since it's "from 0.0.0.0" that I should be able to adjust it.
r7#sh ip eigrp top 9.0.0.0
IP-EIGRP topology entry for 9.0.0.0/8
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2297856
Routing Descriptor Blocks:
0.0.0.0 (Null0), from 0.0.0.0, Send flag is 0x0
Here is what I tried and the "debug ip routing" output
r7#conf t
Enter configuration commands, one per line. End with CNTL/Z.
r7(config)#router eigrp 1
r7(config-router)#distance 255 0.0.0.0 0.0.0.0
r7(config-router)#
r7#clear ip route *
r7#
18:38:38: RT: add 192.168.2.0/24 via 0.0.0.0, connected metric [0/0]
18:38:38: RT: add 192.168.1.0/24 via 0.0.0.0, connected metric [0/0]
18:38:38: RT: add 9.0.0.0/8 via 0.0.0.0, eigrp metric [5/2297856]
18:38:38: RT: network 9.0.0.0 is now variably masked
18:38:38: RT: add 9.9.9.0/24 via 192.168.1.1, eigrp metric [90/2297856]
r7#r
9.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 9.9.9.0/24 [90/2297856] via 192.168.1.1, 00:01:38, Serial3
D 9.0.0.0/8 is a summary, 00:01:38, Null0
I then tried it using an access-list at the end of the distance command
(didn't do anything)
I then also tried it using a "distance 255 0.0.0.0 255.255.255.255" so that
any routes from
anywhere would have a distance of 255 (unreachable) when trying to be placed
into the routing
table. This only filtered the 9.9.9.0/24 from entering the routing table
but the 9.0.0.0/8
was stil there. see Below
r7#r
D 9.0.0.0/8 is a summary, 00:03:15, Null0
C 192.168.1.0/24 is directly connected, Serial3
C 192.168.2.0/24 is directly connected, Ethernet2
r7#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(192.168.1.2)
P 9.0.0.0/8, 1 successors, FD is 2297856
via Summary (2297856/0), Null0
P 192.168.1.0/24, 1 successors, FD is 2169856
via Connected, Serial3
P 192.168.2.0/24, 1 successors, FD is 281600
via Connected, Ethernet2
After all this I have a couple of questions.
1) Is the only way of filtering to get routes out of the routing table is
to use a
"distribute-list in null0"
2) is the distance command applied under the eigrp process only using for
modified
learned routes from a protocol?
Thanks for actually reading all the way down here.
Tim
.
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