From: Aidan Marks (amarks@cisco.com)
Date: Tue Jan 07 2003 - 09:38:59 GMT-3
At 07:06 PM 7/01/2003, Ouellette, Tim wrote:
>How can the summary-address be a AD of 5 when it's directly connected to
>null0.
it is "directly connected" but it is not learned via the "connected"
process but instead known via eigrp, so eigrp can set the AD.
Summary routes in the RIB to null0 are there to prevent routing
loops. Pepelnjak explains this with an EIGRP example on page 185.
Doesn't removing the route via which ever method you might manage to get
working show that you have demonstrated you do not understand this
point? perhaps this competes with the requirements, but there is a
fundamental reason why they exist. best to check with the proctor.
btw, the original need for setting the AD on eigrp summary addresses was to
assist when you wanted to receive a summary and also have a floating
summary on a core router to kick in when a default disappeared from a
border router so that your remote sites (receiving only a summary to reduce
overhead) would still get a summary from the core router instead of losing
complete connectivity from the core.
Aidan
>Try looking at the router that is receiving the summary route and see if it
>gets an AD of 5.
>
>I believe the proper function of eigrp summaries is to add the route to
>null0.
>
>Below is a copy of some testing that I did last week.
>
>Tim
>
>
>
>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
>
>
>
>
>
>
>
>
>
>
>
>-----Original Message-----
>From: cebuano [mailto:cebu2ccie@cox.net]
>Sent: Monday, January 06, 2003 11:58 PM
>To: ccielab@groupstudy.com
>Subject: EIGRP Summary-address behavior
>
>
>Hello.
>I'd like to know if the command "ip summary-address eigrp" as documented
>on CCO has changed. It is described under the command reference as
>follows.
>
>EIGRP summary routes are given an administrative distance value of 5.
>The administrative distance metric is used to advertise a summary
>without installing it in the routing table.
>But I'm getting two conflicting results.
>1. I don't see the admin distance of 5.
>2. I see the summary installed in the routing table.
>
>MC3810a(config-if)#ip summary-address eigrp 2001 150.100.200.0
>255.255.255.0
>
>MC3810a#ir
>
> 150.100.0.0/16 is variably subnetted, 7 subnets, 2 masks
>D 150.100.200.0/24 is a summary, 00:02:41, Null0
>C 150.100.200.0/30 is directly connected, Serial0
>D 150.100.100.0/24 [90/2681856] via 150.100.200.1, 00:02:07,
>Serial0
>D EX 150.100.2.0/24 [170/2195456] via 150.100.200.1, 00:02:07,
>Serial0
>C 150.100.3.0/24 is directly connected, Ethernet0
>D EX 150.100.1.0/24 [170/2195456] via 150.100.200.1, 00:02:07,
>Serial0
>D 150.100.10.0/24 [90/2185984] via 150.100.200.1, 00:02:09,
>Serial0
>
>MC3810a#sh ip eigrp topo
>IP-EIGRP Topology Table for AS(2001)/ID(192.168.254.1)
>
>P 150.100.200.0/24, 1 successors, FD is 2169856
> via Summary (2169856/0), Null0
>P 150.100.200.0/30, 1 successors, FD is 2169856
> via Connected, Serial0
>P 150.100.100.0/24, 1 successors, FD is 2681856
> via 150.100.200.1 (2681856/2169856), Serial0
>P 150.100.2.0/24, 1 successors, FD is 2195456
> via 150.100.200.1 (2195456/281600), Serial0
>P 150.100.3.0/24, 1 successors, FD is 281600
> via Connected, Ethernet0
>P 150.100.1.0/24, 1 successors, FD is 2195456
> via 150.100.200.1 (2195456/281600), Serial0
>P 150.100.10.0/24, 1 successors, FD is 2185984
> via 150.100.200.1 (2185984/176128), Serial0
>
>Any comments?
>Thanks.
>Elmer
>.
>.
.
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