Hi!

> When amanda uses tcp instead of udp for the backup, are all of the tcp 
> connections made from the server to the client?
> 
> How I I force amanda to use tcp instead of udp?

I don't think you can force amandad to use TCP, but I'm not really much of 
an Amanda networking expert. Amanda distribution contains a file 
docs/PORT.USAGE where all this is explained far better than I ever could.

> I have had the backup fail during the day when I run it, but it usuaully 
> fails at night. I think that the estimate times vary and that when the 
> estimate time exceeds some firewall timeout value, then it fails because 
> it no longer fits the iptables "related" rule. Can I use the tcp 
> connections to get around this?

Probably not, because TCP connections will also eventually time out. I've heard
that newer implementations of netfilter have a special Amanda proxy module, but
since I don't use Linux too much I haven't had a chance to try this. I think
your best chance right now is not to rely on ip_conntrack for Amanda connections
but rather allow all traffic between Amanda server and Amanda client regardless 
of tcp/udp state, opening the ports as specified in docs/PORT.USAGE. 
--
Toomas Aas | toomas.aas AT raad.tartu DOT ee | http://www.raad.tartu.ee/~toomas/
* Everyone has a photographic memory. Some don't have film.