MachineA is behind proxy
MachineB is behind MachineA

do i have to configure something on MachineA [one with 2 NICs]
to forward traffic between the two NICs
or it will do automatically???

he i want to help you .But your post is not clear.I mean what are you trying to do.Tell us.

are the two nics on seperate subnets, or the same subnet?

ok let me be more detailed

MachineA has got internet connection
with typical 192.168.x.x static

In order to share the internet connection among the two
Machines
i simply put another NIC in MachineA
I can use the same subnet or different, doesn't matter [i guess]
but MachineB is unable to access the internet connection
Any ideas, how it could be acheived???

well, the easier method would be to have MachineB on a seperate subnet, then do the following :

*) Add a route on your proxy for the MachineB subnet, to point to MachineA

*) On Machine B, set the default gateway to be MachineA

*) Turn on ip forwarding in your networking config on MachineA. I think under fedora it should
be as easy as 'echo 1 > /proc/sys/net/ipv4/ip_forward' in a startup script, or setting an
ip_forward=yes flag in your networking options (not sure where to do this in fedora tho).

*) Add an iptables forwarding rule if you need to (ie: if your FORWARD policy is set to a default
deny)

*) Finally, make sure the proxy can NAT or proxy for the MachineB subnet. If it can't, then
you might have to NAT MachineA onto MachineB, but this could get messy, slow etc. and not
really advised.

Otherwise, depending on what sort of connectivity you want to provide MachineB, you could setup a HTTP/HTTPS/FTP Squid proxy on MachineA, or a general Socks proxy. This would bypass crazy routing stuff entirely.

Having the two machines on the same subnet would involve proxying the MAC's of MachineB and the router for arp requests etc, which you might not be up for doing.

I take it the proxy doesn't have multiple ethernet ports... ?