backroute problem

[Wolfgang Pichler <wpichler@dialog-telekom.at>]

hi all,

we have got new ip addresses - the old one's still exists so that i can
migrate them to the new ones.

the old ip's are directly assigned to the web/mail server (i know that
this isn't good - but i havn't had a fireall at this time) - now i have
a seperate firewall which has the new ip's assigned to it.

Now i'd like to change the dns entries so that the traffic goes over the
new ip's (a 4 MBit line ;-) ) - the problem i have is:

when a packet on the new ip comes then it gets prerouted by the firewall
to the webserver - the webserver gets the packet with the original
source address - now to webserver wants to answer to the packet - but
becuase of the old ip's the webserver have a default route with the old
ip and try's to route the packet over the old gateway - and not back to
the firewall... You know - that can't work.

I am now searching for a solution for this problem. Can netfilter help
me with this problem - or do i have to use iproute (i havn't ever done
something with iproute) help me ?

Can i mark the packet's so the the webserver can send them back in the
right direction ?

mfG
Wolfi