ospf over bgp

Unanswered Question
Nov 26th, 2009

Hi There

I have ospf running as my primary routing protocol i have a back bgp i want my ospf network to know about the bgp but i don't

want bgp to be the preferred route can some tell os the away of accepting inthe bgp routes into the ospf ospf table and changing the admin distance to say 200 on all bgp that are accepted in


Thanks in  advance

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Edison Ortiz Thu, 11/26/2009 - 08:43

Can you provide a diagram of your network?


If you redistribute BGP into OSPF, your OSPF network will receive the BGP routes and if this network is only running OSPF, then there isn't any contention on the route to use as the routers are only running OSPF.


If your OSPF network is also running BGP, are you running eBGP or iBGP?


We need more information about your network topology in order to offer the proper solution.


Regards


Edison.

joycep102 Fri, 11/27/2009 - 00:30

Hi edison


thanks for your reply



we are running ospf on our internal network and where BGP is involved is as a ( telco provider ie a back up link )

i am worried about if redistribute ebgp with a admin distance 20 in to my ospf network with admin distance 110 would the ebgp of 20 be the preferred route ? given that we have a number of sites connected via bgp . am i right in thinking this could case a routing loop?.

so basically i am asking if i an redistribute the ebgp routes into ospf change the admin distance to say 210 on all ebgp routes  on a  ( route map )for example so there not a conflict ?


cheers !!!

vdadlaney Fri, 11/27/2009 - 08:02

joycep102 wrote:


Hi edison


thanks for your reply



we are running ospf on our internal network and where BGP is involved is as a ( telco provider ie a back up link )

i am worried about if redistribute ebgp with a admin distance 20 in to my ospf network with admin distance 110 would the ebgp of 20 be the preferred route ? given that we have a number of sites connected via bgp . am i right in thinking this could case a routing loop?.

so basically i am asking if i an redistribute the ebgp routes into ospf change the admin distance to say 210 on all ebgp routes  on a  ( route map )for example so there not a conflict ?


cheers !!!

Hi, as Edison has mentioned in order to truly understand what you are doing a diagram would be great however per my understanding of the scenario you have provided I have a few questions first


1. Are you running eBGP and OSPF on the same device?

2. Are the routes that you are learning from eBGP and OSPF the same?


I am going to go ahead and assume the answers to the above questions so please understand that the answer might be completely wrong. Assuming that you have a ASBR (device that is running eBGP and OSPF) and assuming that you are learning the same routes than on that ASBR you will prefer the eBGP route due to the admin distance. Now if you go ahead and redistribute that (I have no idea why you would want to do that since you already know the route in your OSPF domain based on my assumption except maybe as a backup route in case your OSPF route disappears) than on the internal OSPF devices once you have lost your native OSPF learnt route only than would the redistributed eBGP route be preferred. The reason for this is that once you redistribute a route into OSPF its an external route and since when everything is running normal your internal route would be preferred over any external route.


Please do correct me if I am wrong. Thx

Edison Ortiz Fri, 11/27/2009 - 10:15

joycep102 wrote:


Hi edison


thanks for your reply



we are running ospf on our internal network and where BGP is involved is as a ( telco provider ie a back up link )

i am worried about if redistribute ebgp with a admin distance 20 in to my ospf network with admin distance 110 would the ebgp of 20 be the preferred route ? given that we have a number of sites connected via bgp . am i right in thinking this could case a routing loop?.

so basically i am asking if i an redistribute the ebgp routes into ospf change the admin distance to say 210 on all ebgp routes  on a  ( route map )for example so there not a conflict ?


cheers !!!

Once you redistribute BGP into OSPF, those routes will be seen in your OSPF network as E1 or E2 OSPF routes (E2 is the default).

Those routes will have an AD of 110 so they will not contend with any other routes, your internal network is only running one routing protocol.


Without seeing a complete network topology, it is very hard to determine a routing loop.


If you provide a diagram with your network topology and points of redistribution, we can help you better.


Regards


Edison.

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