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Apologize for the dumb question, I come from the server world. Our network admin is on holiday and I'm filling in.

For the sake of simplicity, we have a fairly symmetric traffic pattern, what goes up goes down. The setup is VRRP so only one can be the master at a given point of time. Since both are advertising our space on ingress the traffic can come in any path. What seems to be happening is the ISP is naturally splitting our traffic between the links.

On egress though we are prone to saturating a link. Looking at the bandwidth graphs the VRRP master is sending all the egress traffic and the VRRP backup is sending none. This seems to make sense as Juniper, per their docs, prefers an eBGP route over iBGP.

As a test we moved the links on router B over to router A and traffic naturally split 'evenly' on egress as well.

Is there a way to have the iBGP routes have equal preference to the eBGP routes? We do get full table from our ISP on both the routers and each has a backup static router hard coded to the PE. The desired goal to mimic the behaivor when all circuits were plugged into RA. Some of the traffic would flow directly out carrier-A plugged into the router and some would get handed off to B? We would have to have some mechanism to prevent routing loops so RouterB doesn't try the same trick and hand it back to routerA.

Topology is as follows: https://i.stack.imgur.com/tONtV.jpg

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  • This related question contains an answer (from me) explaining why eBGP routes are considered superior/unequal to iBGP routes. It's an important property of BGP's loop-prevention strategy. networkengineering.stackexchange.com/questions/68938/…
    – Jeff Wheeler
    Sep 4, 2020 at 16:57
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin ♦
    Dec 17, 2020 at 21:22

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On egress though we are prone to saturating a link. Looking at the bandwidth graphs the VRRP master is sending all the egress traffic and the VRRP backup is sending none. This seems to make sense as Juniper, per their docs, prefers an eBGP route over iBGP.

First, BGP has a detailed path selection process that can vary slightly per vendor, but this particular item is a function of the protocol itself, not Juniper's implementation.

Second, the idea behind this behavior is that you'd want to get traffic off of your network as quickly as possible (your ISP in this case). Otherwise, you'd have to haul traffic from the VRRP master to the backup via IBGP and then outbound. You could do this in your case, but it's a bit more complex to implement and shouldn't be your first choice. Router A is taking all of the traffic because of VRRP, not BGP.

Using BGP to accomplish what you're looking for is a pretty big hammer, you may consider leveraging VRRP for this instead. For example, let's say that you have a /24 that is using Router A as master and Route B as backup, you can split that into 2 /25s and make Router A master and Router B backup for the first /25, and Router B master and Router A backup for the second /25.

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  • Thanks for the response. That's a great idea but would require reconfiguration of end gear that points to those default gateways. I think were going to do this the old fashion way and get the account manager to give us the ports! How would this scenario work if you had two carriers? Carrier A on R1, Carrier B on R2. If you did the VRRP method you would potentially get suboptimal routes as only Carrier A would be used. If you had A and B plugged into R1 BGP will properly do it's thing on egress.
    – MicrosoftGuy908234
    Sep 4, 2020 at 20:20
  • You’re right about having to change the gateways with VRRP, it’s something to consider for sure. Your topology only indicates one carrier, so I was operating under that assumption, if you had 2 carriers what you said is possible. I know you want to just make an IBGP route look like an EBGP route, but it doesn’t work like that (see Jeff’s comment as well), it isn’t the same as moving all of your ISP links to the same router. As you said, if you are able to add other links toward your carrier on the different routers that would work.
    – Jordan Head
    Sep 5, 2020 at 15:27

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