Prefer OSPF route to BGP

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Dec 8th, 2009
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Hi,

I have a headquarters site with a single router that has two links.  One link is an OSPF link via Metro and the second is an eBGP link via MPLS.  There are multiple remote sites at the far end with an OSPF and eBGP link also into a single router in each site.  If I want traffic to take the OSPF route as the primary path what is the best practise method to make eBGP the less perferrable path?

Thank you

Brian

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Jon Marshall Tue, 12/08/2009 - 09:25
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Brian.oflynn wrote:


Hi,

I have a headquarters site with a single router that has two links.  One link is an OSPF link via Metro and the second is an eBGP link via MPLS.  There are multiple remote sites at the far end with an OSPF and eBGP link also into a single router in each site.  If I want traffic to take the OSPF route as the primary path what is the best practise method to make eBGP the less perferrable path?

Thank you

Brian


Brian


Two options -


1) Can you summarise the remote networks across the BGP link so that the OSPF routes are more specific and are always used as long as the OSPF link is up ?


2) If not you can look to manipulate the AD (Administrative Distance). Either change OSPF to below 20 or increase EBGP to above 110.


Jon

Brian O'Flynn Tue, 12/08/2009 - 09:48
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Hi Jon, Option 1 is out unfortunately. I had been looking into option 2 but it seems to be an all or nothing when it comes to changing admin distance.  Wasn't sure if there was a more granular way of doing it with a route map.


Cheers

Brian

marpina Tue, 12/08/2009 - 09:33
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I think, you can use the BGP backdoor that makes the IGP route the preferred route.

It's depend of the topology but maybe help you.


router bgp 1

neighbor 1.1.1.1 remote-as 2

network 10.1.1.0 backdoor


Best regards

Marcelino

marpina Tue, 12/08/2009 - 10:29
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Hi Brian,


I found out interesting file, Can you check this file that mentioned using the "weight" value
that one prefix with the higher weight will be installed in the
routing table based on the BGP best path selection process
but you can play with this value.


https://supportforums.cisco.com/docs/DOC-5748


I hope this help
Marcelino

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