Re: [LARTC] multiple gateway problem

[Whit Blauvelt <whit@transpect.com>]

Ross,

The diagram really helps. My guess is what you need to do is put a second
address on eth0, and then differentiate your packets according to which
address they have arrived at on the Linux box - for example, 10.4.44.11 or
10.4.44.12.

And yeah, there should be a way to do it by MAC address, but this should be
simpler.

Whit

On Tue, Dec 04, 2001 at 02:11:37PM -0800, Ross Simpson wrote:
> First off, here's a diagram:
> 
> 
>                I N T E R N E T
>                /              \
>    -------------             -------------
>    | 10.4.44.1 |             | 10.4.44.2 |
>    |  lucent   |             |   speed   |
>    -------------             -------------
>     port-fw 80                 port-fw 80
>               \               /
>                \             /
>                 \           /
>                  -----------
>                  |   hub   |
>                  -----------
>                       |
>                       |
>                       |
>                       |
>                      eth0
>                 --------------
>                 | 10.4.44.11 |
>                 |   linux    |
>                 --------------
> 
> I have a default gateway as specified in /etc/sysconfig/network:
> 	GATEWAYDEV=eth0
> 	GATEWAY\x10.4.44.1
> 
> I ran the below commands to use multiple default gateways.
> 
> So here's what I would _like_ to see:
> 	Traffic coming to the box from the internal network uses the default route
> from /etc/sysconfig/network.
> 	Traffic coming from the internet (from the 10.4.44.1 router, then
> port-forwarded 10.4.44.11) should use 10.4.44.1 as the gateway to return the
> packets to the client.
> 	10.4.44.2 should work identically to 10.4.44.1.
> 
> Right now, traffic coming from the system default gateway works great.
> Traffic coming from 10.4.44.2 gets to the system, however I would guess that
> it's being sent back to 10.4.44.1 as it is the default gateway.
> 
> As I'm watching a tcpdump, I see that packets are coming in with their
> original (external) IP addresses, instead of the address of the router (I
> was thinking that port forwarding temporarily changed the source IP of the
> packet; apparently not).  So the setup is not working because external IPs
> don't match 10.4.44.1 or 10.4.44.2, and the system's default gateway is
> used.
> 
> So, I guess my question becomes: is there any way for linux to tell which
> router the packet came from?  Could it tell maybe by mac address?
> 
> Thanks for the help!
> Ross

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