[asterisk-users] Routers that do not show external IPs...
Stefan Schmidt
sst at sil.at
Thu Oct 14 14:51:58 CDT 2010
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
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