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I have a Brocade FESX648-PREM switch that is currently connected to an IXP and a single upstream transit provider. This switch accepts the default route via BGP from the transit provider. I announce a few prefixes to the transit provider.

I would like to add another uplink of equal speed from a second transit provider to multi-home. However, my switch is not able to accept the full routing table.

Would it be possible to accept a default route from the second transit provider as well as the first provider? What sort of configuration would I need to load balance between the two uplinks? It seems to me that two static default routes with equal weight could work... but I'm not certain.

  • When you say load-balance and talk about the routes you're receiving, I'm assuming this question is only concerned with outbound load-balancing from your site... correct? – Mike Pennington Aug 30 '14 at 9:38
  • Yeah, outbound load balancing is what I'm trying to achieve. I imagine that inbound would be out of my control if both uplinks are announced the same prefixes, right? – Elliot B. Aug 30 '14 at 18:45
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    Prepending your ASN multiple times will give you very rough control over proportions of inbound traffic between the links; but that's a pretty blunt tool. – Mike Pennington Aug 30 '14 at 20:10
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No, that won't work that way. Your switch will select one of those two as default, most likely the one with the lowest IP address. One way to solve this is of course buy a real router capable of handling two full feeds, but there are other solutions which may work. You could ask both your transit providers to announce the default route as two /1's or four /2's (etc). That way you can use local preferences to prefer parts of the routing table via each provider. Of course, load balancing based on prefixes is no guarantee that you're actually balacing traffic ratios evenly.

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    FYI, scanning through the Brocade docs, I found a command which allows outbound load-balancing for default routes from different ASNs. maximum-paths ebgp 2 and multipath multi-as would give him egress ECMP for his defaults received from a different ASN, no? – Mike Pennington Aug 30 '14 at 10:06
  • I'm working with a Brocade FESX648-PREM. The command maximum-paths ebgp 2 isn't accepted, but the commands multipath ebgp and maximum-paths 2 are accepted. Anyone know if this is the full command set required? I'll test this out more properly once I can get a second default route via BGP setup. – Elliot B. Aug 30 '14 at 18:55
  • The commands you mentioned help, but you definitely want multipath multi-as; otherwise, take Teun's very solid guidance about requesting 1.0.0.0/1 and 128.0.0.0/1 from your upstreams. – Mike Pennington Aug 30 '14 at 20:06

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