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Configuring EIGRP with neighbor command

Posted on 2016-10-29
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I have seen EIGRP configuration where the use Neighbor keyword as well as without Neighbor keyword.

Can someone explain the difference ?

Thank you
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Question by:jskfan
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by:Predrag Jovic
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EIGRP neighbors configured with neighbor command - use unicast traffic for communication with neighbors, without neighbor keyword traffic is muticast traffic (although not completely - ACKs are unicast).
With that said - all neighbors in shared segment should be configured with neighbor command otherwise they can't establish neighbor relations.
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by:jskfan
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multicast , you are referring  to 224.0.0.10 ?

well, if you have separate sites connected through WAN mediums, then you will configure Neighbors just at the site level, not between sites. Correct ?

if so then do you configure (kind of Bridge head routers) between sites with Neighbor command ?
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by:Predrag Jovic
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multicast , you are referring  to 224.0.0.10 ?
Yes.
well, if you have separate sites connected through WAN mediums, then you will configure Neighbors just at the site level, not between sites. Correct ?
Typically no, since you don't want company traffic to be unencrypted - so you would typically use some encrypted tunnel. In this case for example if you use IPsec - multicast is not supported so you can configure EIGRP neighbors with neighbor command. The same case is with frame relay - broadcast and mulicast are not supported, so if you configure neighbors with neighbor command - routers can become neighbors.
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by:jskfan
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I believe the company I worked for used : Ethernet Services over fiber
they use EIGRP , and they have separate sites, distant 20 miles apart

I guess you can use Multicast with Ethernet Services over fiber.
However if there is lost of connection on Site3, the queries will be sent all over other sites..
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by:Predrag Jovic
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That depends on type of connection. Some types allow multicast, some don't. Also security is another question... There are some types of tunnels that allow multicast traffic etc....

What I wrote is general approach, however, it can be used in a different manner depending on design.
However if there is lost of connection on Site3, the queries will be sent all over other sites..
It is always like that. Any time network is lost - queries will be sent. That is how EIGRP router asks neighbors do they know how to reach networks that were previously in routing table and have no feasible successor ready.
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by:jskfan
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- I thought with Neighbor command.. it means you are  limiting  the router to which other router it can send the Query to.
 

- When Multicast is used... I  do not know when query is sent to Multicast address,  whether any router can reply to it, or there is specific router that can reply to it.
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by:Predrag Jovic
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No. Query will be sent to all EIGRP neighbors in any case.
That is question:
"Do you know how to reach network X.X.X.X? I had that network in my routing table and lost it"
And sure, since it is not known what router can have alternative route to network... Question will be sent to all EIGRP neighbors...

Typically you would use summarized routes and EIGRP stub to control queries.
not sure, but I believe I already wrote it previously.
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by:jskfan
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OK Jovic...
Where it is not clear is:
If you manually configure neighbors... then the router who lost routes will query the neighbors specified with Neighbor command

If  there is no Neighbor command configured... then the router who lost routes will query all routers in the network ?
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by:Predrag Jovic
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No, in both cases queries will be sent to all neighbors.

The only difference is how neighbors communicate with each other...
unicast vs multicast...
Everything else should be the same.

Cisco's explanation in FAQ
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by:jskfan
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so if you want to form EIGRP adjacency between just some specific routers and not with others, how can you achieve that ?

Thank you
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by:Predrag Jovic
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You can configure neigbors with neigbor command, you can use passwords for EIGRP neighbors, use different EIGRP AS number etc...
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by:jskfan
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Creating different AS numbers sounds good idea.
Now if you have 2 separate AS number , each AS has 5 Routers, and you want just one of  router from AS 1 to  get the updates from another Router of the other AS 2
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by:Predrag Jovic
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Not sure what would be benefit there, but you can always do redistribution between ASs.
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by:jskfan
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I just though you could contain the queries within each site.
Only the Edge router can Fetch external routes for the routers within its site
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by:jskfan
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Or set up Authentication different on each site
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by:jskfan
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You can configure neigbors with neigbor command, you can use passwords for EIGRP neighbors, use different EIGRP AS number etc...
Would this isolate each site ?
and how do you bridge them ?
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by:Predrag Jovic
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For example password authentication is per interface. You can bridge and/or isolate by setting different passwords on different interfaces.
However, typically you want your neighbors to connect to as many neighbors as possible so you can have alternative routes to destination if possible. EIGRP will calculate best path and add it to routing table (if there is no route with better AD).
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by:jskfan
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by:Predrag Jovic
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I read that article few years back.
However, we are far far away from original topic:
I have seen EIGRP configuration where the use Neighbor keyword as well as without Neighbor keyword.
:)
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by:jskfan
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Yeah initially I thought when you use Neighbor keyword, you are limiting the queries just between routers specified  by Neighbor command.
However you stated that it is not the case. This is why I kept looking for a solution that limits the Queries within the site, though the Edge router on each site still can communicate between themselved and propgate routes.
probably the link I posted can accomplish that ?
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Predrag Jovic earned 500 total points
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Yes, typically summary routes are the best way to go.
If you summarize routes on neighboring routers, typically query will be drastically reduced. Neighbors tell to each other - You were advertising that network, I have no idea about it. So, router that sent query will get response really fast and network will be either deleted or route will be replaced with new route.
:)
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by:jskfan
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I believe When you summarize..you are just reducing the size of the routing table.

Let's say site3 Edge Router R33 is connected to the routers in the DataCenter (Site1)
on Site3 we want R44 ,R55,R66,R77 never queries the routers in the Datacenter, they will query just R33 (Edge Router) or they can query between themselves within their site.
how do you do that ?
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by:Predrag Jovic
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I believe When you summarize..you are just reducing the size of the routing table
Once again, believing will get you nowhere. You need to know it.

As much as I am concerned you can believe in anything.
Have a good life.
:)
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by:jskfan
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Jovic..
sorry I made this thread too long..I promise it will end up soon (:-)

What I thought of , if I am not wrong,
you can leave the Edge router as it is, and the routers within that site configure  them with static routes, which means Anything you do not know forward it to the Edge Router

Only the Edge router will have Eigrp , the rest within that site will be static route
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Thank you
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