Router with 2 (or more) interfaces in same network

Leo Bicknell bicknell at
Tue Nov 11 16:03:46 UTC 2003

In a message written on Tue, Nov 11, 2003 at 10:34:31AM -0500, Richard A Steenbergen wrote:
> I'm not sure how Cisco is wrong on this one. If you want 2 router
> interfaces to have the same route and you actually want both of them to
> work, it means at the very least you must have a non point-to-point
> medium, such as Ethernet. In this case, the correct configuration would be 
> a bridge-group and IRB, creating a virtual routed interface with 2 
> physical ports for bridging.

Correct config yes, however it doesn't have some of the load balancing
properties the other "hack" method does.

Given how many other ways Cisco will let you shoot yourself in the
foot, this particular "feature" seems odd.  I've asked about it
before though, and it seems to a under-the-hood issue due to the
way they do arp.

> I love FreeBSD, but it's routing code is probably the thing you least want
> to look to for examples on how things should be. BTW there is a netgraph
> module for L2 hash-based load balancing (aka etherchannel without the
> PAgP/LACP), but yeah the lack of ECMP and a reasonable switching method to
> support it falls into the category of the previous sentence. :)

Well, s/FreeBSD/{Linux,SunOS,HP-UX,OSF/1,probably others}/.  I've
seen this done a lot with various unix boxes.  Never tried on a
Juniper.  My point was simply that there are boxes that will let
you do this, and that some people do it with great success to solve
specific problems.  Doesn't mean it's not a hack, or that an ISP
should "support" that type of configuration.

       Leo Bicknell - bicknell at - CCIE 3440
        PGP keys at
Read TMBG List - tmbg-list-request at,
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