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Beginner

eBGP Traffic engineer best practice

Hi,

I have 2 routers in a branch which will connect to 2 other router in a DC via eBGP. R1 in branch connecting to R1 in DC and R2 in branch connecting to R2 in DC. What options do I have here? Should I configure router 1 in branch as the outgoing and incoming traffice for all ? i.e setting worse AS-Path on R2 in branch so R1 in branch gets the incoming traffice and also Settings Local prefernce higher on R1 branch so outgoing packets also go through R1. This will make it an active passive scenario for the routers. Or I can mix match some subnets to each router so that both links are used. Just want to confirm if the Idea is right here.

 

THanks

 

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Collaborator

Hi,

   

    Regardless if you use eBGP or iBGP between the branch and DC, as long as you have an iBGP peering between the routers from the branch and an iBGP peering between the routers from the DC, you'll make use of the local-preference attribute, easiest way, to influence path selection between DC and the branch.

   As for load-balancing or sending all traffic over one ISP, it's your call, but ensure that traffic flows symmetrically between any given subnet A from the branch and subnet B from DC (so both A to B and B to A flows over the same path). I, personally, make the call based on the available BW over both paths, always trying to load-balance the non-tehchnical requirements with choosing the most efficient and effective possible solution. If the BW for at least one ISP is enough to sustain all traffic, which should be, i would do it this way, cause it also allows the technical solution to be simpler, thus less prone to errors, bugs, accidental config changes which affect the traffic, etc.

 

Regards,

Cristian Matei.

 

Regards,

Cristian Matei.

  

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So iBGP between the routers on each side is a must for local preference to take affect ?


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Hi,

 

   Both routers from both sites (branch and DC) will get the routes from the other side over the BGP peering. As you would want to ensure that specific traffic (A to B), or all traffic goes through the let's say R1(branch) to R1(DC) path, you have two options:

    - ensure that routing in the branch side (default gateway if all LAN's are locally connected to the router) and routing on the DC side is done in such a way that traffic destined for the other side always reached R1, as if it reaches R2, R2 will send it via its direct path; this requirements can be achieved, based on the routing/topology design, easier or less easier. This is not the recommended option as you have to keep this in mind with al further change you do in the network

    - you have iBGP peering between R1-R2 on both DC and branch, In which case, due to the local preference settings and the iBGP peering, both routers (R1 and R2) from both sides (branch and DC) will prefer the exit path via the R1 routers; you no longer need to ENSURE (though it's still recommended to avoid too much inter router routing from within the same site) that traffic from A to B or all traffic (depending o your end policy) needs to reach R1, as otherwise it may be routed via the R2 path if it reaches R2.

 

Hope everything is clear.

Regards,

Cristian Matei.

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VIP Expert

Another option would be to use PfR to dynamically direct flows across your two paths to optimize bandwidth utilization. The later PfR variants are QoS aware so you can also insure time sensitive traffic is given the best performing path.
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