Prefer BGP routes over EIGRP

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Jun 3rd, 2008
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Hi,


I have two links from site A to Site B one link 2 MB is directly connected and other one is of 4 MB thru the service provider. I'm using EIGRP b/w Sites.


Using EBGP b/w router A-SP & SP-B for the service provider network. On router C I'm seeing the Router B network routes which are redistributed into EBGP. Everything is fine so far.


On site A Router A EIGRP topology contains two routes one learned thru EIGRP (Rtr B) n other one thru EIGRP-EBGP (Rtr C) and Router A injecting routes learned thru EIGRP internal) even though the BGP learned routes are having less metric, I think its due to external routes.


I want the Site A to use the path A-C-B, instead of A-D-B, irrespective of route type internal/external/etc....and backup path as A-D-B.


Any suggestions please. I have attached the sample image.


Regards,



Attachment: 
Correct Answer by scottlivingston about 8 years 11 months ago

actually, w/ the setup I just gave you will need to use the bgp distance command, as rtr-a will still pref the WAN EIGRP AD of either 90 or 170 over the IBGP 200.


scott


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scottlivingston Tue, 06/03/2008 - 05:46
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Though there are many ways to skin this cat, (say in a home lab) I will offer feedback based off the assumption this is production environment.


Can you replace your EIGRP A-D-B w/ eBGP?...if so, that would make it very simple w/ a local pref manipulation back @ site-A after you config both rtr-a and rtr-c for IBGP.


If you can't get rid of the EIGRP over the WAN transit rtr-d then try this….. Smoke the EIGRP session BETWEEN rtr-c and rtr-a, but leave EIGRP on the both if needed (for over the WAN and on the backend LAN @ site-A). Redistribute your EIGRP routes from the WAN into BGP. Manipulate the local-pref between the BGP session for rtr-a and rtr-c and make it pref the path transit rtr-a.


If you can't get rid of the EIGRP between rtr-a and rtr-c you can use the BGP 'distance' command to manipulate the routes…. You need that IBGP AD=200 beat out that EIGRP 90 and 170 AD…. need to make it smaller than AD=90.

http://www.cisco.com/en/US/docs/ios/12_1/iproute/command/reference/1rdbgp.html#wp1113874


Like I said, there are many ways to do this, but each has to be weighed against your needs and how you want things to converge. If you don't like either of these options I'll give you a floating static route design. :)


scott


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scottlivingston Tue, 06/03/2008 - 05:53
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actually, w/ the setup I just gave you will need to use the bgp distance command, as rtr-a will still pref the WAN EIGRP AD of either 90 or 170 over the IBGP 200.


scott


aijaz802 Fri, 06/06/2008 - 22:13
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Hi All,


Thanks for the replies. As of now I have used the distance command and its working fine. Thanks for all the help..

Harold Ritter Tue, 06/03/2008 - 05:51
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Aizaz,


You could summarize routes on router D towards router A and router B, so that specific routes via the SP cloud will always be preferred.


Regards,

scottlivingston Tue, 06/03/2008 - 07:14
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Harold,


that is a much better idea! good thinking! boy i'm getting rusty! :)


scott

Harold Ritter Tue, 06/03/2008 - 07:19
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Scott,


As you said so well, there is more than one way to skin a cat. The beauty of NetPro is that there is many posters with different ideas. The original poster can then evaluate all of these ideas and use the one that best suits his needs.


Thanks for your contribution to NetPro.

standardbankcco Mon, 06/09/2008 - 03:53
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Hi,


I have a similiar problem.

I have two links from site A to Site B one link 2 MB is directly connected and other one is of 4 MB thru the service provider. I'm using EIGRP b/w Sites.

Using BGP b/w router A-SP & SP-B for the service provider network.

On router C I'm seeing the Router B network routes which are redistributed via eigrp 100 into BGP.

On router E I'm seing Router D network routes, which are known via eigrp 100.


On Site A router A I only see routes from router E.


I want the Site A to use the path A-C-B, instead of A-E-D, irrespective of route type internal/external/etc....and backup path as A-E-D.


Please find image attached. Any help would be appreciated.


Thanks!



Attachment: 
Harold Ritter Mon, 06/09/2008 - 04:47
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You could simply summarize EIGRP routes from router E to router D and vice versa. This way the BGP routes will be more specific an therefore preferred over the EIGRP routes.


Regards,

standardbankcco Mon, 06/09/2008 - 07:29
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Thanks.


Is it possible to put more than one 'ip summary-address eigrp' statement on an interface?

Harold Ritter Mon, 06/09/2008 - 11:20
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Yes, it is certainly possible to enter many of these statements under the same interface.


Regards,

standardbankcco Tue, 06/10/2008 - 00:14
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Thanks. I will try this out, out of hours this weekend.


I will be summerising the below networks:


10.211.48.0

10.211.53.0

10.220.64.0

10.209.2.120 loopback


ip summary-address eigrp 100 10.208.0.0 255.240.0.0


Please let me know if this is correct.


Regards,

Irfaan

standardbankcco Tue, 06/10/2008 - 02:12
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The summary statement, above, will be applied to Router E on Site A. The summary statement encompasses networks, which are in Site B i.e 10.220.1.0, 10.213.20.0, etc.


Would it be better to make the summarisation more specific or would it be ok to leave as is?


Could I have the summary statement below on router E & Router D?


ip summary-address eigrp 100 10.0.0.0 255.0.0.0


Sorry for all the questions!

Harold Ritter Fri, 06/13/2008 - 04:18
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I was referring to the following statement:


ip summary-address eigrp 100 10.208.0.0 255.240.0.0



Regards,

standardbankcco Mon, 06/16/2008 - 00:58
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I have applied the statements and everything is working as desired.


There is just one small issue. It takes 3 1/2 mins to failover to the backup link. Is there anyway to to reduce this time?


Thanks for your help.

Harold Ritter Mon, 06/16/2008 - 04:55
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This sounds like the maximum it would take for BGP to declare the session down. You could definitely reduce the BGP hold timers to get a better convergence time going from the BGP to EIGRP path.


Just out of curiosity, how did you test the BGP failure?


Regards,

standardbankcco Tue, 06/17/2008 - 01:27
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I shut the interface down on the remote site and basically timed how long it would take to reach the site again.


Convergence from EIGRP to BGP was quicker and without any ICMP drops.


Harold Ritter Wed, 06/18/2008 - 05:29
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You should modify the BGP keepalive and hold timers to reduce the delay in BGP to EIGRP convergence.


Regards,

standardbankcco Fri, 06/20/2008 - 02:16
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What would be a suitable setting for the keepalive, say if I wanted to reduce the hold timer to 60 sec?


Would this be a stable setting?



Harold Ritter Fri, 06/20/2008 - 03:54
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You could easily go lower than 60 seconds without jeopardizing the stability of the network. What is your convergement requirement? Would 30 seconds be enough? I have seen many networks running with values lower than that without any issues.


Regards,

standardbankcco Fri, 06/20/2008 - 06:05
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30 seconds is good.

Would be good if was even lower.


Can this change be done for one site or does it need to be done on all BGP sites?

Harold Ritter Sat, 06/21/2008 - 18:40
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You could probably go lower than 30 seconds but be careful.


If you want the convergence time to be the same for all sites then you need to change the default for all sites.


Regards,

standardbankcco Sun, 06/22/2008 - 14:50
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I changed the keepalive to 10 sec and the hold timer to 30.


I tested it by bringing down the link, but it took around 2 1/2 for the rerouting to take place.


Any ideas why this would happen with the given values?

standardbankcco Mon, 06/23/2008 - 00:00
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BGP neighbor is 62.6.17.17, remote AS 12641, external link

Description: VPNv4 to PE2-DXB-ME

BGP version 4, remote router ID 62.6.19.199

BGP state = Established, up for 09:19:13

Last read 00:00:03, last write 00:00:02, hold time is 30, keepalive interval is 10 seconds

Configured hold time is 30,keepalive interval is 10 seconds Minimum holdtime from neighbor is 0 seconds

Neighbor capabilities:

standardbankcco Thu, 06/26/2008 - 00:07
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should I use the 'neighbor X.X.X.X fall-over' in the BGP process for faster convergence?

sdoremus33 Sat, 06/21/2008 - 09:01
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ip summary-address eigrp 100 10.208.0.0 255.240.0.0


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