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bgp routing

If I’m adverting one network out of a router via BGP to 5 locations and I standup another router to advertise that same network but want to target one router only to have that router use the path of the new router what would be the best way to manipulate BGP in that manner?

 

Router A in production advertising network 192.168.1.0/24 to 5 locations all works well.

Router B is a new router that needs to advertise 192.168.1.0/24 but only target one out of the 5 locations and not affect any of the 4 locations so the remainder of the 4 use Router A and the last location uses Router B without the use of tunnels.

 

Thanks,

J

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Hall of Fame Super Blue

JI don't think you are going

J

I don't think you are going to be able to do this with BGP because as you say there is no direct peering between the routers.  So you are reliant on the SP and their routing but there is no way to say to the SP use router B to get to this network but only from a specific site.

If the remote site was meant to use router B for all prefixes and all the other sites use router A then you could simply have router B and the remote site in their own VRF but i suspect this is not the case.

Even if it was it would require reconfiguration on the SP side and you would have no failover between router A and B which you may want.

I think tunnels may be your only option to be honest.

Jon

15 REPLIES
Hall of Fame Super Blue

JDo you want router B to

J

Do you want router B to advertise the network to all sites but have four of them still prefer router A or do you want router B to only advertise to the site you want to use that path ?

If you want it advertised to all sites but only one site uses it there are a couple of ways to do depending on how it is setup.

So are all the routers peering with the same AS ie. is it an MPLS setup ?

In addition i think you are still going to have configure something locally on the router you want to use router B.

Perhaps you could give some more details ?

Jon

Hall of Fame Super Gold

J I agree with Jon that it

J

 

I agree with Jon that it would help if we had a better understanding of your environment and of your real requirements.

 

Based on my limited understanding I would suggest this as an alternative. I think that you are telling us that router B needs to peer with one neighbor and advertise a specific network to that neighbor. I do not see anything that says that router B needs to peer with the other 4 routers. This would be the most simple solution to have router B establish a peer relationship with the one peer and not with the other peers.

 

HTH

 

Rick

New Member

router B does not peer with

router B does not peer with any of the routers but it requires a network advertisement out to one site only across the MPLS and I only want to target 1 out of the 5 sites to recieve this network.

My first thought was tunnel interface between router b and the spoke router in scope and just route the network over that interface to contain that network between router b and the spoke router but I wanted to see if there is a BGP option.

 

Hall of Fame Super Gold

J I am confused. You tell us

J

 

I am confused. You tell us that you want Router B to advertise to one router and then you tell us that "Router B and the other routers do not peer at all". If Router B is not peering with other outers at all then how will it advertise the network?

 

HTH

 

Rick

New Member

Sorry I might be using the

Sorry I might be using the wrong terminology but let me add more information.   
 
Router A/B sit in the same data-center and are advertising network 192.168.1.0/24 via the  
router bgp  
Network statements  
Router bgp 65001
Network 192.168.1.0 mask 255.255.255.0
Exit
 
The remote sites sit across an MPLS network and they only peer with the PE (provider edge routers) and not with Router A or Router B but they learn the networks that Router A and Router B advertise.  
 
The requirement is for Router B to advertise the same network 192.168.1.0 / 24 out to the MPLS and target only one site out of the five sites.  
 
 
 

 

 

 

 

Hall of Fame Super Blue

JI don't think you are going

J

I don't think you are going to be able to do this with BGP because as you say there is no direct peering between the routers.  So you are reliant on the SP and their routing but there is no way to say to the SP use router B to get to this network but only from a specific site.

If the remote site was meant to use router B for all prefixes and all the other sites use router A then you could simply have router B and the remote site in their own VRF but i suspect this is not the case.

Even if it was it would require reconfiguration on the SP side and you would have no failover between router A and B which you may want.

I think tunnels may be your only option to be honest.

Jon

Hi Jon, I agree tunnels would

Hi Jon,

 

I agree tunnels would be the easiest way.

 

But possibly some excercise with route targets on the provider side (more sophisticated than a separate VPN) could reach the goal?

 

Best regards,

Milan


 

Hall of Fame Super Blue

Hi MilanDo you mean using

Hi Milan

Do you mean using import/export maps to control which routes are imported into the VRF on the PE devices ?

If so then yes assuming that the remote site router's PE device had no connections from any of the other remote sites otherwise i'm not sure how it would work.

I was assuming that the OP was looking to control it from their end ie. no SP intervention.

Perhaps you were thinking of something else ?

Jon

 

Hi Jon,as we agreed the only

Hi Jon,

as we agreed the only way how to handle this request from the customer side would be some tunnels involved, I was thinking about it as a small challenge for the SP.

 

My idea was to use something similar to this:

http://packetlife.net/blog/2013/jun/10/route-distinguishers-and-route-targets/

 

So a unique route-target export value (b) would be used in the VRF connecting router B and added to the current route-target import value (a) in the VRF connecting the single site which should use router B to enter the data centre. Plus it would be necessary to configure some preferences there to assure the prefix received from router B's VRF would be preferred.

All other sites could use a different route-target export an value (a). This value would be also used as the route-target import on all sites.

 

Shouldn't this work?

Maybe I could configure something like that in my lab "when I have some free time".

 

Best regards,

Milan

 

 

 

 

 

Hall of Fame Super Blue

Hi MilanYes i think that

Hi Milan

Yes i think that might work as long as router A, B and the remote site router all peered with different PE devices and none of other remote sites shared either the router B or single remote site PE. 

If any of the PEs were shared i think that could cause difficulties in terms of the importing and exporting.

You would as you say still need to prefer one route over the other on the remote site PE although if no failover was required another option would be to filter the router A advertisment with an import map controlling which routes get placed into the VRF.

Jon

 

Hall of Fame Super Gold

J The additional information

J

 

The additional information is helpful. I wonder if communities might provide a BGP solution. If you set a particular BGP community value on the advertisement of the prefix on Router B and set a different BGP community value on the advertisement of the prefix on Router A could you then do filtering on the community value on the remote sites such that the one site would accept the advertisement from Rotuer B while the other remote sites accept the advertisement from Router A?

 

HTH

 

Rick

Hall of Fame Super Blue

RickI think that would work

Rick

I think that would work if the routers peered directly with each other.

But the problem is that they are peering with the SP PE routers. So to a remote site the next hop is the PE whichever route it accepted ie. the one from router A or the one from router B.

So it is the PE routers where any configuration needs to be done.

Jon

New Member

Hi Jon,I would like router B

Hi Jon,

I would like router B to advertise the nework to only one site if possible and not advertise to any of the other sites at all since some I manage and others I do not.

Router B and the other routers do not peer at all and this is over a MPLS network.

Router B site at the edge of the data-center and the other sites are spokes across the MPLS cloud.

 

Hello,If you want any one of

Hello,

If you want any one of the routers to chose the new router in BGP as the next hop then provide the local prefernce higher than which you have at Old router (default value is 100 and you can go higher to it.)

Example

router bgp 650xx

neighbor <new router ip>  route-map pathtonetwork in

!

route-map pathtonetwork permit 10

set local-preference 200

If your requirement is something else please elaborate it as said by Mr Jon and Richard.

 

Regards

Thanveer

Please Rate the Helpful Posts.

Regards Thanveer "Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."
New Member

Hi Thanveer,This is good info

Hi Thanveer,

This is good info but router B does not peer with any of the other routers since the other routers sit across an MPLS network.

Thanks,

Juan

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