From: j killion (jkillion1977@xxxxxxxxx)
Date: Thu Jan 10 2002 - 10:26:20 GMT-3
Once you added the "auto-summary" cmd, EIGRP will now
summarize at network boundaries - in this case at
20.0.0.0/8. It creates the summary pointing to Null0
to stop routing loops from forming.
--- Steven <adream@163.com> wrote:
> 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?
>
>
>
> Thanks.
>
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