[asterisk-users] Routers that do not show external IPs...

[Stefan Schmidt]

Am 14.10.2010 21:06, schrieb Tim Nelson:
> 
> The TCP header is exactly what the NAT changes, no?
> 
> --Tim
> 

to the outside yes but not inside.

for example thats how a typical nat table looks like. (its from a zyxel
adsl router with nat)

========================Nat session table==============================
Slot Prot   Int-IP  :Port    Out-IP  :Port    Ext-IP  :Port  Idle
=======================================================================
  45 TCP  192.168.0.1    :6023  xxx :6023  zzz  :44450 0
 121 UDP  192.168.0.129  :5061  xxx :10619 sip1:5060  4
 135 UDP  192.168.0.129  :5060  xxx :10618 sip2:5060  3

========================Summary information=============================

192.168.0.129 is a sip phone with 2 accounts registered to sip1 and sip2.

if i take a look at sip1 i will see the package from ip xxx port 10619.
Ofcourse its behind nat but i will see in the contact header
192.168.0.129 port 5061. With sip ALG active also the contact header
would be changed to xxx port 10619.
Other way if i look on the phone i see the answer from sip1 directly as
a message from sip1 port 5060 and not from xxx port 10619 or 192.168.0.1.

several things wont work if you dont get the original source ip through
a nat router.

thats how i have learned it and see it everyday in practice.

best regards

stefan