Routing Problem

Thomas Foster tbonius at
Wed Feb 2 04:55:25 PST 2005

Hi Tim..

If you have multiple interfaces and you configure a default gateway for each 
interface, the default metric determination that is based on the speed of 
the interface usually uses the fastest interface for default gateway 
traffic. This is usually desirable in configurations in which the computer 
is connected to the same network.

This behavior can become a problem when the computer exists on two or more 
disjointed networks (networks that do not provide symmetric reachability on 
layer3). Symmetric reachability exists when packets can be sent to and 
received from an arbitrary destination.

Because the TCP/IP version4 protocol uses a single default route in 
FreeBSD's routing table at any one time for default route traffic, default 
routers configured on multiple interfaces connected to two or more 
disjointed networks can wreak routing traffic havoc.

 In FreeBSD, you can manually configure the routing table for the individual 
interfaces..  but it sounds to me as if you are attempting to use two 
ethernet interfaces connected to two disjointed networks connected to 
routers with two seperate subnets in order to balance http requests to one 
server.. is this the case?  I guess I am not fully understanding your 
configuration ...


----- Original Message ----- 
From: "Gustafson, Tim" <tjg at>
To: "Thomas Foster" <tbonius at>
Cc: <questions at>
Sent: Wednesday, February 02, 2005 4:06 AM
Subject: RE: Routing Problem

> Thomas,
> No, I'm not using this box as a router.  It is a web server, and I need
> to spread the load of my web traffic across two separate T1s.
> I can't just add routes.  You need a default route, or parts of the
> internet would become inaccessible.  In my case, you need TWO default
> routes.  I have set up Cisco equipment and Windows workstations with two
> default routes in the past, and it has worked.  In fact, I have one
> Windows box right now that is configured on both these networks with two
> default gateways, and it is working.
> There has to be a way to make it work on FreeBSD.
> Tim Gustafson
> MEI Technology Consulting, Inc
> tjg at
> (516) 379-0001 Office
> (516) 480-1870 Mobile/Emergencies
> (516) 908-4185 Fax
> -----Original Message-----
> From: Thomas Foster [mailto:tbonius at]
> Sent: Wednesday, February 02, 2005 4:48 AM
> To: Gustafson, Tim
> Cc: questions at
> Subject: Re: Routing Problem
> Im confused.. if you have two T1s, then are using /30s dor the ranges?
> If
> so.. what about not giving a default gateway for either one and just add
> routes...
> Are you attempting utilize this as just a router.?
> Theres a section that covers setting up routing on interfaces in the
> handbook:
> g.html
> Hope this helps
> T
> ----- Original Message ----- 
> From: "Gustafson, Tim" <tjg at>
> To: <freebsd-questions at>
> Sent: Tuesday, February 01, 2005 5:35 PM
> Subject: Routing Problem
>>I am having a problem setting up a multi-homed host.  I have two
>> separate T1 internet connections, and one physical NIC in my FreeBSD
>> box.  The two networks are as follows:
>> Connection 1:
>> LAN Address:
>> Router Address:
>> Connection 2:
>> LAN Address:
>> Router Address:
>> I would like to set up my FreeBSD box so that I can connect to either
>> LAN address from the outside world.  The problem is that I cannot
>> specify two default gateways.  Right now, I have set up as a
>> default gateway, and I can get to the IP from the outside
>> world.  However, I can't get to  I can't even ping it.
> From
>> the FreeBSD box, I can ping, and from the outside world I
> can
>> ping, but I can't ping from the outside world.
>> Is there any way to make this work?  How can I make FreeBSD have two
>> default gateways?  I read somewhere about being able to set up source
>> routing, but I haven't been able to find any HOWTO's about that.
>> Any help is greatly appreciated.

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