[Serusers] no audio if clients are behind different nat

31 Jan 2005

      Hi,

I have the exact same problem as described in the below email which I
found on the serusers mailing archives. That is clients behind the
same nat can ring each other and transmit audio but if a client tries
to ring a client behind another nat no audio is transmitted.
According to the below email this is because the sdp is not rewritten
correctly. The below solution mentions calling force_rtpproxy but
that function is called in the original config (see below)...Is there
a specific plce that it should be invoked?

Thank you,
Aisling.

You have to call force_rtpproxy -> this will rewrite the IP address
and 
port with the one of the rtpproxy.

klaus

Sun Yen-Rong (Dan) wrote:
...
Hi Klaus,
Firstly, thanks for your help. I used ethereal to capture the SIP
messages, and found out that the SDP in the forwarded INIVITE and
200 OK
message are not rewritten correctly. As a result, the client with a
public IP address is sending RTP packets to the private IP address
of
the other client who is behind a NAT. One seruser suggested me to
use
fix_nated_sdp("3") instead of fix_nated_sdp("1"), however, it didn't
solve my problem. Do I also need to add a parameter to other
nathelper
functions as well?
Regards,
Dan.
-----Original Message-----
From: Klaus Darilion [mailto:klaus.mailinglists at pernau.at] 
Sent: Thursday, May 06, 2004 9:45 PM
To: Sun Yen-Rong (Dan)
Cc: serusers at iptel.org
Subject: Re: [Serusers] no audio problem if clients behind NATs
use a packet sniffer (ethereal or ngrep) and watch the SIP messages
at 
the SIP proxy. Take a look at the sdp in the forwarded INVITE and
200 OK
message and verify that the IP address and port in the SDP are
rewritten
correctly and points to the rtpproxy.
regards,
klaus
Sun Yen-Rong (Dan) wrote:
...
Hi all,
I am using ser 0.8.12 with nathelper and rtpproxy. When I tried to
make
...
a call between two clients which are behind the same NAT, everything
work fine. However, when I try to make a call between clients which
are
...
behind different NATs, niether client can hear each other's audio.
my
configuration file is shown in the end of this message. Can someone
help
...
me, please?
Thanks,
Dan.
#
# $Id: nathelper.cfg,v 1.1.2.1 2003/11/24 14:47:18 janakj Exp $
#
# simple quick-start config script including nathelper support
# This default script includes nathelper support. To make it work
# you will also have to install Maxim's RTP proxy. The proxy is
enforced
...
# if one of the parties is behind a NAT.
#
# If you have an endpoing in the public internet which is known to
# support symmetric RTP (Cisco PSTN gateway or voicemail, for
example),
...
# then you don't have to force RTP proxy. If you don't want to
enforce
# RTP proxy for some destinations than simply use t_relay() instead
of
# route(1)
#
# Sections marked with !! Nathelper contain modifications for
nathelper
...
#
# NOTE !! This config is EXPERIMENTAL !
#
# ----------- global configuration parameters

...
...
debug=3         # debug level (cmd line: -dddddddddd)
fork=yes
log_stderror=no	# (cmd line: -E)
check_via=no	# (cmd. line: -v)
dns=no           # (cmd. line: -r)
rev_dns=no      # (cmd. line: -R)
port=5060
children=4
fifo="/tmp/ser_fifo"
# ------------------ module loading

...
...
",#
# $Id: nathelper.cfg,v 1.2 2003/04/15 20:35:29 jiri Exp $
#
# example script showing use of nathelper module 
# (incomplete for sake of brevity)
#
# ----------- global configuration parameters

...
...
# ------------------ module loading

...
...
loadmodule "/usr/local/lib/ser/modules/sl.so"
loadmodule "/usr/local/lib/ser/modules/tm.so"
loadmodule "/usr/local/lib/ser/modules/rr.so"
loadmodule "/usr/local/lib/ser/modules/maxfwd.so"
loadmodule "/usr/local/lib/ser/modules/usrloc.so"
loadmodule "/usr/local/lib/ser/modules/registrar.so"
loadmodule "/usr/local/lib/ser/modules/textops.so"
# !! Nathelper
loadmodule "/usr/local/lib/ser/modules/nathelper.so"
# ----------------- setting module-specific parameters

...
...
# -- usrloc params --
modparam("usrloc", "db_mode",   0)
# -- rr params --
# add value to ;lr param to make some broken UAs happy
modparam("rr", "enable_full_lr", 1)
# !! Nathelper
modparam("registrar", "nat_flag", 6)
modparam("nathelper", "natping_interval", 30) # Ping interval 30 s
modparam("nathelper", "ping_nated_only", 1)   # Ping only clients
behind
...
NAT
# -------------------------  request routing logic

...
...
# main routing logic
route{
# initial sanity checks -- messages with
  # max_forwards==0, or excessively long requests
  if (!mf_process_maxfwd_header("10")) {
      sl_send_reply("483","Too Many Hops");
      break;
  };
  if (msg:len >=  max_len ) {
      sl_send_reply("513", "Message too big");
      break;
  };
# !! Nathelper
  # Special handling for NATed clients; first, NAT test is
  # executed: it looks for via!=received and RFC1918 addresses
  # in Contact (may fail if line-folding is used); also,
  # the received test should, if completed, should check all
  # vias for rpesence of received
  if (nat_uac_test("3")) {
      # Allow RR-ed requests, as these may indicate that
      # a NAT-enabled proxy takes care of it; unless it is
      # a REGISTER
if (method == "REGISTER" || ! search("^Record-Route:"))
{
...
log("LOG: Someone trying to register from private
IP,
...
rewriting\n");
# This will work only for user agents that support
symmetric
...
# communication. We tested quite many of them and
majority is
...
# smart enough to be symmetric. In some phones it
takes a
...
configuration
          # option. With Cisco 7960, it is called
NAT_Enable=Yes, with
...
kphone it is
          # called "symmetric media" and "symmetric
signalling".
...
fix_nated_contact(); # Rewrite contact with source
IP of
...
signalling
          if (method == "INVITE") {
              fix_nated_sdp("1"); # Add direction=active to
SDP
...
};
          force_rport(); # Add rport parameter to topmost Via
          setflag(6);    # Mark as NATed
      };
  };
# we record-route all messages -- to make sure that
  # subsequent messages will go through our proxy; that's
  # particularly good if upstream and downstream entities
  # use different transport protocol
  if (!method=="REGISTER") record_route();
# subsequent messages withing a dialog should take the
  # path determined by record-routing
  if (loose_route()) {
      # mark routing logic in request
      append_hf("P-hint: rr-enforced\r\n"); 
      route(1);
      break;
  };
if (!uri==myself) {
      # mark routing logic in request
      append_hf("P-hint: outbound\r\n"); 
      route(1);
      break;
  };
# if the request is for other domain use UsrLoc
  # (in case, it does not work, use the following command
  # with proper names and addresses in it)
  if (uri==myself) {
if (method=="REGISTER") {
# Uncomment this if you want to use digest authentication
#			if (!www_authorize("iptel.org", "subscriber")) {
#				www_challenge("iptel.org", "0");
#				break;
#			};
save("location");
      	break;
      };
lookup("aliases");
      if (!uri==myself) {
      	append_hf("P-hint: outbound alias\r\n"); 
      	route(1);
      	break;
      };
# native SIP destinations are handled using our USRLOC
DB
...
if (!lookup("location")) {
      	sl_send_reply("404", "Not Found");
      	break;
      };
  };
  append_hf("P-hint: usrloc applied\r\n"); 
  route(1);
}
route[1] 
{
  # !! Nathelper
  if (uri=~"[@:](192\.168\.|10\.|172\.(1[6-9]|2[0-9]|3[0-1])\.)"
&&
...
!search("^Route:")){
      sl_send_reply("479", "We don't forward to private IP
addresses");
...
break;
       };
# if client or server know to be behind a NAT, enable relay
  if (isflagset(6)) {
      force_rtp_proxy();
  };
# NAT processing of replies; apply to all transactions (for
example,
...
# re-INVITEs from public to private UA are hard to identify as
  # NATed at the moment of request processing); look at replies
  t_on_reply("1");
# send it out now; use stateful forwarding as it works reliably
  # even for UDP2TCP
  if (!t_relay()) {
      sl_reply_error();
  };
}
# !! Nathelper
onreply_route[1] {
   # NATed transaction ?
   if (isflagset(6) && status =~ "(183)|2[0-9][0-9]") {
       fix_nated_contact();
  force_rtp_proxy();
   # otherwise, is it a transaction behind a NAT and we did not
   # know at time of request processing ? (RFC1918 contacts)
   } else if (nat_uac_test("1")) {
       fix_nated_contact();
   };
}
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Ashling O'Driscoll

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