[CentOS] control outgoing IP address?

That depends on the application. You can specify the outgoing IP address
for postfix with ``smtp_bind_address'' in main.cf. The inn NNTP server
uses ``sourceaddress'' in the inn.conf file, etc.

Bill

There may be settings in each application that control that, but in case
there are not .. you should be able to do something like :

iptables -t nat -A POSTROUTING -p tcp --sport 334 -j SNAT --to 2.3.4.5

Barry

Is there no way to control the default source address?

In some applications you can .. but it is application dependent. what
applications are you looking to do this with?

Barry

Don't take this as a definitive answer, but I have multi-aliased CentOS
boxen.

I find that outgoing connections always come from the main IP address,
not the aliases. In particular these boxen are web servers hosting
multiple sites, hence the multi-IP and connections to the database all
appear to be from the main IP.

Applications can be attached to individual IPs, but I think the default
routing is to use the main IP of the interface.

I didn't try it, but you probably can control that with the "ip route"
command when you create a route to a specific network or a default
route.

Maybe try something like:

# ip route add default via [Gateway_Address] dev [Interface] src [Alias_Address]

Maybe the syntax is not 100% right, "man ip" might help you.

You can also use this IP for outgoing connections only to some
specific destinations, by using a more specific network address
instead of "default".

You will probably have to remove the default gateway configuration
from /etc/sysconfig/network and add this "ip route" command somewhere
(rc.local?).

Anyway, let us know if you got it to work!

HTH,
Filipe