BGP per-flow load balancing between eBGP and iBGP learned prefix

Baldur Norddahl baldur.norddahl at
Fri Sep 19 17:02:36 UTC 2014


Your problem is that the LB will only deliver traffic to one router. You
then want that router to send half of the traffic to the other router via a
default route. But that is unsound: The other router would be configured
with a similar multipath default route and send half of the traffic right
back to the first router, creating a loop.

You need the routers to be able to deliver traffic to both provider next
hops directly. This can be done by clever use of VLAN or MPLS tunneling.
Let me try to describe the VLAN option:

Put provider link 1 on VLAN 100 and provider link 2 on VLAN 200. Make sure
both routers have access to both VLANs. Make a static host route (/32) on
the router that is not speaking BGP on that VLAN. The host route would
point to the provider next hop on the VLAN. Now you have the same L3
distance to both next hops and multipath routing can do the rest.



On 16 September 2014 17:33, Andy Litzinger <andy.litzinger.lists at>

> Hello,
> I have a Load Balancer that uses a default route to a VRRP IP hosted
> between two Juniper MX80 routers.  Each MX router has a single BGP feed
> from the same provider and each session is currently receiving only a
> default route.
> I'd like to load balance my outbound traffic across the two links.  More
> specifically I want to balance traffic to a particular prefix across the
> two links so even if i was receiving full routes trying to manually split
> prefixes to a second upstream VRRP instance wouldn't help.
> I believe the typical way to do this would be to run an IGP between the LB
> and the MX's so that each MX advertises a default route to the LB and let
> ECMP take care of it.  I'm not averse to this long term, but I have a short
> term need and the LB requires a license to participate in an IGP.  Is there
> another way?  I should note that the LB will not let me enter multiple
> default or identical static routes so I can't try spinning up a second VRRP
> session and adding a second default route on the LB to it.
> Is it possible to let BGP do the load balancing?  From what I can tell this
> would be trivial if both of the provider links were terminated on the same
> router via a few multipath config lines but because they are on different
> routers I seem to be running into the "eBGP > iBGP" Path selection criteria
> which prevents the routes from being equal.
> I appreciate any ideas!
> regards,
>  -andy

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