[TriLUG] sourcing outbound traffic from internal NIC

[Clay Stuckey]

already tried a few variations in the /etc/sysconfig/network-scripts/  
folder. There are a few options found when googling. The syntax might  
be a little too complex. I am leaning towards just hacking it into  
the /etc/init.d/network init script for now.


On Dec 6, 2009, at 3:52 PM, Tom Barron wrote:

> Well, instead of driving this off a timer, you can run a script when  
> the
> interface comes up.  Where you put the script depends on your OS  
> flavor.
> On Debian/Ubuntu systems, you could add a little script to
> the /etc/network/if-up.d/ directory.  On RedHat/Centos, check
> out /etc/sysconfig/network-scripts/,
> probably /etc/sysconfig/network-scripts/ifup-routes.  Slackware,  
> gentoo,
> etc. have other hooks.
>
> On Sun, 2009-12-06 at 14:34 -0500, Clay Stuckey wrote:
>> I found part of the solution. Ip route default via [gw ip] src [int
>> ip]. I have to remove the default gw first. This handles the issue at
>> layer 3. My only issue is now to find the right way to make it  
>> persist
>> a network restart. At the moment, I have a cron job that checks for a
>> gw and will execute the ip route command if needed.
>>
>> --
>> Clay Stuckey
>> (919) 600-0486
>> claystuckey at gmail.com
>>
>> On Dec 6, 2009, at 2:27 PM, Aaron Joyner <aaron at joyner.ws> wrote:
>>
>>> What IP traffic is sourced from can be determined by the application
>>> (based on what IP it binds to, or what IP it received traffic on),  
>>> so
>>> you can't necessarily do this at the OS layer.  You can't do it w/ a
>>> route, as that will only control where the traffic is routed (ie.  
>>> what
>>> interfaces it traverses, and ultimately where it leaves the box),  
>>> not
>>> what the source IP of the traffic is in the IP header.  You can make
>>> it appear to remote hosts like all traffic has come from that IP,  
>>> sort
>>> of, by SNAT'ing traffic from the "internal" IP, but that may not be
>>> what you actually want.  Can you provide some more details about  
>>> what
>>> original goal led you down this technical path?  If so, someone can
>>> likely provide a good suggestion to accomplish what you're after.
>>>
>>> Aaron S. Joyner
>>>
>>>
>>> On Sun, Dec 6, 2009 at 11:02 AM, Clay Stuckey
>>> <claystuckey at gmail.com> wrote:
>>>> I have a machine with 2 NICs. One is internet facing, the other
>>>> internal.
>>>> Anyone know of a way to have all internet-bound traffic sourced
>>>> from the
>>>> internal NIC's IP? I am thinking entering a default route rule that
>>>> will
>>>> specify to use the internal NIC. Has anyone tried this before?
>>>>
>>>> Clay
>>>>
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>>>>
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> -- 
>  Tom Barron
>  tbarron at dyncloud.net
>  +1 919-619-7572
>
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