[asterisk-users] SIP AND NAT

[Ketema Harris]

I recently did a set up where I replaced a simple D-link home router  
that was having trouble processing a T1's worth of bandwidth with a  
linux machine running iptables.  the kernel was 2.6.29-r5 and I chose  
the SIP connection tracking modules from the menuconfig.

Router worked fine for normal traffic, but I was unable to get the SIP  
phones to work.  Using ngrep it was plain to see that the although the  
packets going out were reaching their destination the data inside the  
sip headers all contained non routable IPs.  I used lsmod and saw that  
the following modules:

nf_nat_sip              5084  0
nf_nat                 16400  3 nf_nat_sip,ipt_MASQUERADE,iptable_nat
nf_conntrack_ipv4      11912  3 iptable_nat,nf_nat
nf_defrag_ipv4          1788  1 nf_conntrack_ipv4

were loaded.  I also googled and found the http://www.iptel.org/ 
sipalg/ website, but since this seemed to be a little dated I assumed  
the modules contained in the kernel source tree were newer and more  
"reliable"

my questions are: What is the correct way(or resource to find a way)  
to get a linux firewall to work with SIP so that the NAT issue is not  
an issue ?