[clug] asymmetric routing

David Schoen neerolyte at gmail.com
Wed Aug 26 02:56:29 MDT 2009

Your outgoing (or uploads) should go wherever your next hop is
(default gateway if something more specific doesn't match it first).

Your incoming traffic is determined by routers outside of your control
(in this situation at least) but should be based only on the IP the
traffic came from (and there for where it wants to go back to).

What's likely to happen in this situation is that you'll be stuck
behind a proxy/nat/something-else-designed-purely-for-evil that will
mean the IP your 3G device knows about has no relevance to the IP the
end point knows about.

That's my understanding anyway.


2009/8/26 Chris Zhang <chris.zhang.syd at gmail.com>:
> If I make the phone the default gateway, wouldn't all traffic (both outgoing
> and incoming) be sent through to that interface? What connections would be
> ultilising the USB 3G connection?
> I tested it and tcpdumped the traffic, it appears that the other IP (USB
> connection) is not used.
> Chris
> On Wed, Aug 26, 2009 at 4:48 PM, Craig Small <csmall at enc.com.au> wrote:
>> On Wed, Aug 26, 2009 at 04:11:03PM +1000, Chris Zhang wrote:
>> > I am wondering if there is a way to tweak the routing table or the
>> firewall
>> > to dedicate all downloads through the USB dongle and keep my uploads
>> through
>> > my mobile connection? That is, for a normal tcp connection, all
>> > acknowledgments get sent out via the phone 3G connection?
>> Making the phone the default gateway would do it.  The problem is
>> I'm not sure if the 3G will let you do this.  A standard network, sure
>> you can often send packets with the "wrong" IP address as the source but
>> I'm not sure 3G ones will let you do this.
>> As far as the other network is concerned, you're spoofing the source
>> address and a lot of places filter that.
>>  - Craig
>> --
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>> http://www.enc.com.au/                             csmall at : enc.com.au
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