On the subject of multihoming

Scott Doty scott at sonic.net
Wed Nov 12 17:18:05 UTC 2008

[ resent to list, was sent from the wrong address -sd ]

Charles Wyble wrote:
> I'm working on a small experiment which utilizes multiple outbound 
> links (in the experiments case multiple consumer 3G connections [to 2 
> Sprint/2 Verizon/1 AT&T], Time Warner Cable Modem and an SBC Global 
> DSL connection.
> What is the best way to do outbound traffic engineering? I would like 
> to be able to determine the best path possible and send traffic out 
> the appropriate link.

Not sure if this is useful, but I thought I'd contribute a point on the

from NANOG 9:


Obquote: from Paul Vixie's presentation,
from Stan Barber's notes, here is the "meat of the matter":

_ _ _ _ _ _ _
Per-interface Default Route

    * BSD TCP binds outbound route to PCB on SYN-ACK
    * Our trick: remember the inbound interface identity from the SYN
    * Each interface has its own "default route"
    * For outbound TCP and all UDP, a normal default is also needed.

_ _ _ _ _ _ _

Hope that helps...


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