How does the OS decide which source IP address to put into an outgoing packet?

[Matthew Melvin]

On Tue, 5 Apr 2005 at 5:28pm (+0200), David Tonhofer, m-plify S.A. wrote:

> Hi,
>
> I was just wondering how the OS (in this case, RH ES 3.0)
> decides which IP address to put into an outgoing packet.
>
> I have an interface with several IP addresses assigned to it,
> i.e. there I have the following setup:
>
> eth0:   - IP address 1 on subnet 1, a /28 subnet
> eth0:0  - IP address 2 on subnet 1, a /28 subnet
> eth0:1  - IP address 1 on subnet 2, a /27 subnet
> eth0:2  - IP address 2 on subnet 2, a /27 subnet
>
> I always thought outgoing packets would have the address of
> eth0. To my surprise, they have the address of eth0:1.
>
> If anyone has a hint on why this might be so, please do tell.
>

If you add 'NO_ALIASROUTING=yes' to ifcfg-eth0 that ought to stop it and 
always make eth0 the source instead of the aliases.

M.

-- 
:wq!