Admin distance Eigrp summary route

Answered Question
Jan 21st, 2010
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Hi,

We have three routers R0--> R1-->R2 connected by serial point to point link.

On all Eigrp is running and working properly. When we summazie routes on R0 on ser 1/0

ip summary-route eigrp 1 10.10.0.0 255.255.0.0.  This route is advertised to R1 and R2 but admin distance

shown is 90. I was wondering if that should be 5 as that route is eigrp summary route.

From R2 I am able to ping 10.10.1.1 which is interface on R0. That means summarization is working.

Please share the experience.

Thanks in advance.

Subodh

Correct Answer by Jon Marshall about 7 years 6 months ago

Subdoh


Just to add to Giuseppe's post.


The summary route is AD 5 on the local router only. And as Giuseppe said the next-hop of that route on the local router is always null0. The reason for it being lower than any internal/external EIGRP is to prevent routing loops. So traffic that matches the summary address will be sent to this router. If this router does not have a more specific route for the destination then you want that traffic to be dropped, hence the reason the AD is set to 5 so it takes priority over any internal or external EIGRP routes.


Jon

Correct Answer by Giuseppe Larosa about 7 years 6 months ago

Hello Subodh,

you should find a static route to nullo with AD 5 on router where you have configured the ip eigrp summary route.

It is important to remember that EIGRP creates this static route to nullo with AD 5, because it can create problems.


suppose you want to send out only a default route. Without adding a final parameter like 200 that will be the AD of the static route to null0 the risk is that default route of local node is overriden by the static to null0 creating a black hole.


neighbors will classify the route as EIGRP internal route, so you cannot see AD 5 on them.

what you see is normal


see


ip summary-address eigrp as-number ip-address mask [admin-distance] [leak-map name]


http://www.cisco.com/en/US/docs/ios/iproute_eigrp/command/reference/ire_i1.html#wp1019434




Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Thu, 01/21/2010 - 07:00
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Hello Subodh,

you should find a static route to nullo with AD 5 on router where you have configured the ip eigrp summary route.

It is important to remember that EIGRP creates this static route to nullo with AD 5, because it can create problems.


suppose you want to send out only a default route. Without adding a final parameter like 200 that will be the AD of the static route to null0 the risk is that default route of local node is overriden by the static to null0 creating a black hole.


neighbors will classify the route as EIGRP internal route, so you cannot see AD 5 on them.

what you see is normal


see


ip summary-address eigrp as-number ip-address mask [admin-distance] [leak-map name]


http://www.cisco.com/en/US/docs/ios/iproute_eigrp/command/reference/ire_i1.html#wp1019434




Hope to help

Giuseppe

bapatsubodh Fri, 01/22/2010 - 05:30
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Hi,

Thanks a lot,  cleared one more "concept" !!

Thanks

Subodh

Correct Answer
Jon Marshall Thu, 01/21/2010 - 07:45
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Subdoh


Just to add to Giuseppe's post.


The summary route is AD 5 on the local router only. And as Giuseppe said the next-hop of that route on the local router is always null0. The reason for it being lower than any internal/external EIGRP is to prevent routing loops. So traffic that matches the summary address will be sent to this router. If this router does not have a more specific route for the destination then you want that traffic to be dropped, hence the reason the AD is set to 5 so it takes priority over any internal or external EIGRP routes.


Jon

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