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Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

2018-11-15 15_50_54-BGP-Recursive-Routing-Test - GNS3.png

 

 

 

The obvious fix is for R1 and R2 to have a static route to the gi1/0 IP address of their neighbor. One possibility of allowing router 1 and 2 to both be used for internet would be to set the weight on each router.

 

route-map Set-BGP-Attribute permit 10

set weight 65535

 

router bgp 65500

neighbor neighborIP route-map Set-BGP-Attribute in - This is gi1/0 neighbor.

 

Please respond with a couple of different examples how you deal with BGP routing out two different internet circuits when you are not getting the full internet routing tables. I know we could set the metric or use prepending, but is there a best practice?

 

2 ACCEPTED SOLUTIONS

Accepted Solutions
VIP Mentor

Re: Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

Hello,

 

are R1 and R2 iBGP neighbors ? If so, you can use local preference...

Beginner

Re: Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

To solve your next hop issues, there are two normal methods:

  • Set R1 & R2 to use next-hop-self
  • use a BGP network statement on R1 & R2 covering their respective links to R3 & R4

This assumes that R1 & R2 are iBGP neighbours, which they should be.

 

Hope this helps,

 

Dave

5 REPLIES 5
VIP Mentor

Re: Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

Hello,

 

are R1 and R2 iBGP neighbors ? If so, you can use local preference...

Contributor

Re: Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

 I was thinking since weight is local to the router that it gets set on, setting the weight would be a good option for this particular setup.  R1 and R2 are iBGP neighbors.  Do you have any issues with using the weight over local preference in this case?

Beginner

Re: Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

To solve your next hop issues, there are two normal methods:

  • Set R1 & R2 to use next-hop-self
  • use a BGP network statement on R1 & R2 covering their respective links to R3 & R4

This assumes that R1 & R2 are iBGP neighbours, which they should be.

 

Hope this helps,

 

Dave

Contributor

Re: Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

This seems like a solid solution. I was just going to do static routes for R1 and R2 respective links. I am going to use weight since I want traffic to flow out both sides and we are receiving the longer as-path from one of the ISPs. Do you have any comments on that?

Beginner

Re: Multi-Homed BGP Best Path Selection and Next-Hop inaccessible

Hi Alex,

 

Yes, weight is about the only way that you could do this, since every other metric is shared across the whole AS. You can't use eBGP multipath because your uplink routers are in different ASs. I have to say that I tend to avoid using weight because it is only pertinent to the individual router and can cause routing loops if not used carefully. You may be able to gain some load sharing by taking larger BGP tables from your service provider (e.g. default and Provider-local AS). 

 

Hope this helps

 

Dave

 

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