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Q: What softphone work with siproxd?

A: The goal is that every softphone (that is SIP compliant) should be
   able to work via siproxd. Tested and/or reported to work so far:
   - linphone (
   - kphone   (http://
   - MSN Messenger
   - Grandstream BudgeTone series
   - X-Lite   (
Q: Is it possible from a remote computer to call the inbound computer?

A: Yes, see also next question.
Q: What SIP address must the remote computer use to make a call?

A: Scenario

   private IP address range             :          Internet
   10.0.0.x                             :          (public IP address range)
   +-------------+             +--------------+              +-------------+
   !             !.10       .1 ! masquerading ! publicIP     !             !
   ! IntHost     !-------------! Firewall     !------------>>! externalHost!
   !             !         eth0!              !ppp0          !             !
   +-------------+             +--------------+              +-------------+
   user: johndoe                                               user: test                                                       

  - IntHost is running an SIP softphone (like linphone, kphone)

   - The SIP address used by IntHost is

   - The softphone on IntHost is configured to register at siproxd
     running on the firewall host ( as

   - is the domain name corresponding to the public IP address
     of the firewall (eg use some dynamic DNS service [1])

   - externalHost does *not* register at siproxd running on the firewall host.

  The relevant part of the configuration (linphone) of IntHost 
  then looks like ($HOME/gnome/linphone):


  To make an outgoing call from IntHost simply use the SIP address of the
  target ( -> can make a incoming calls - it simply has to use the registered
  SIP address of the softphone running on IntHost (
  Siproxd will then rewrite and forward the incoming request to Inthost.

  The externalHost does not need to know anything about the proxy. For the
  user it looks as he directly sends the traffic to, siproxd then takes care about where to send it from there.

Q: How does the registration and mapping of inbound clients work?

A: The mapping mechanism of SIP addresses works basically like:

   Inthost sends a registration to siproxd with:
   - a 'To:' address of the address to be registered (
     (lets call this address the 'masqueraded' or 'public'  address)

   - a 'Contact:' address of the *true* address (sip:johndoe@

   Siproxd then will basically 'just' substitute the true address by the
   masqueraded address and vice versa. That means you can have multiple
   IntHosts (each of them using a different user name) running at the
   same time.

   For an incoming call, siproxd will search its registration table for
   the requested SIP address and so finds the internal host that belong to it.

   This of course *requires* that the username part of the SIP address is
   unique for each softphone that registers a the proxy (So this is more or
   less the mechanism that you mentioned in your mail).
Q: How does the RTP Proxy work?

A: The RTP proxy actually is quite simple. It does not use any RTP
   protocol stack.  All relevant code is located within rtpproxy.c.
   The RTP proxy is running as a separate thread. It maintains a
   list of active RTP transfers (rtp_proxytable).
   Controlling (registering a new RTP data stream / removing a RTP stream)
   is done via 2 service routines rtp_start_fwd() and rtp_stop_fwd() from
   withing the SIP related part of siproxd.
   When a session is established (INVITE, ACK), siproxd will fetch the
   relevant information (UDP ports) from the SIP messages and
   does a rtp_start_fwd().
   This will create an UDP socket and binds it to the outbound interface
   address (port number dynamically chosen withing the RTP port range).
   In addition a entry into the rtp_proxytable will be made.
   The RTP Proxy then *simply* does wait withing a select() to receive
   a UDP datagrams on the specified ports and then sends them to the
   local client. The RTP proxy does absolutely not care about WHAT data
   is proxied, so it is not aware of RTP or any other high level stuff.
   It is simply a binary forwarding of datagrams.
   If the session is closed (BYE) the RTP stream will be stopped via
   rtp_stop_fwd(). In addition, there exists a timeout supervision
   (configurable) that will stop RTP streams that have been inactive
   (no data received) for a specified time.
Q: Does siproxd need to be installed on the same host as the
   firewall / NAT is running?

A: Not necesarily. Siproxd needs to know the public IP address, as this
   address is included in the SIP signalling to establish a session. Also,
   siproxd needs control on the allocation of UDP ports for sending/receiving
   RTP data (some User Agents get into trouble/silence if the sending and
   receiving UDP port is not the same)
   However, siproxd does *not* interact with ipchains/iptables. The
   requirement for the firewall rules is to allow port 5060 for incomming
   UDP datagrams (SIP) as well as the UDP port range for RTP data as
   specified in the config file (default 7070 - 7079).
   One mode of operation is to run siproxd on the NAT host, using
   different if_inboude and if_outbound interfaces.
   The other method is to ruin siproxd "in front of" the NAT firewall.
   For configuration details see the documentation (host_outbound).
Q: How do I configure siproxd to use ICPHAINS based UDP masquerading
   tunnels for proxying the incomming RTP traffic?

A: Since version 0.5.2, IPCHAINS and IPTABLES are no longer supported.
   Use the RTP relay instead.
Q: What types of operation does siproxd support?

A: Siproxd can be used in two ways:

   1) Siproxd as outbound proxy:
      - Configure your local client to register with some 3rd party service
        like Sipphone, FWD, Sipgate or any other.
      - Configure your local client to use siproxd as OUTBOUND PROXY

      Note: In this case, the local client does NOT register with siproxd
      but only with the external SIP restration service. The only condition
      is that siproxd needs to stay in the path of communication, therefore
      the local client must be configured as to use an OUTBOUND PROXY.

   2) Siproxd as registrar:
      If you don't want to use any 3rd party service, you can have your
      local clients directly with siproxd. Only in this case you should
      set-up accounts and passwords in siproxd.
      - Configure you local client to register with siproxd. As AOR (address
        of record) choose a user part as you want and a host part that
        resolves to the public addess of the host running siproxd.
      - DO use siproxd as outbound proxy

      Note that siproxd has very limited capabilities when used as
      registrar. So my recommendation is to use method 1) and go with
      a real registrar.

Q: How do I use siproxd as a pure outbound proxy, so I can register with my
   SIP phone at a third party registrar?

A: Also Simple. Just configure your SIP phone to use siproxd as outbound
   proxy and your 3rd party registrar as registrar. Siproxd will then
   transparently handle (and if needed rewrite) the SIP traffic.
Q: I have a Grandstream Budgetone-100 SIP phone. The SIP communication
   seems to work properly (I can register, make and receive calls) but
   I do not hear any audio. However, transmitting audio works.

A: Since version 0.5.2, IPCHAINS and IPTABLES are no longer supported.
   Use the RTP relay instead. Grandstream SIP phones are now working
   properly with the RTP relay.

Q: I use Linux (kernel 2.4.x) with ipchains. However, siproxd
   always complains "ERROR:IPCHAINS support not built in", why?

A: Since version 0.5.2, IPCHAINS and IPTABLES are no longer supported.
   Use the RTP relay instead.

Q: I  have two local UA (SIP phones) connected to siproxd. I can
   make outgoing calls and receive incoming calls to some other
   SIP phones in the internet. However, making a call between the
   two locally connected does not succeed, why?

A: Since Version 0.5.3 this is supported.

Q: When I'm experimenting with siproxd, sometimes it is not enough to
   restart siproxd to get rid of old junk.

A: Siproxd remenbers the registrations made by UAs in a seperate file.
   Therefore, just restarting siproxd is not enough to get rid of them.
   Of course eventually they will time out and be removed from the cache.
   You also can delete the cache file default it is in
   - stop siproxd
   - rm siproxd_registrations
   - start siproxd

Q: I have problems getting MSN Messenger 5.0 to work (using FWD
   as 3rd party registrar).

A: First make sure that you have an SIP enabled MSN messenger, which
   is a separate download from the non-SIP-enabled Messenger 5 at

   For the configuration, enter the local IP address of siproxd as the server
   and as your address. When the authentication
   dialog comes up you must use your FWD_NUMBER (266xxx) and your password.
   Messenger misleads you into typing which 
   will fail...

Q: Can you give an example configuration for kphone and FWD?

   (FWD_NUMBER is your FWD account number)

   Full Name: My Name
   User part of SIP URL: FWD_NUMBER
   Host Part of SIP URL:
   Outbound Proxy:          <<-- local IP of siproxd
   Authentication Username: FWD_NUMBER
   q-value:                             <<-- empty

   Socket Protocol: UDP
   Use STUN Server: No
   Symmetric Signalling: No             (may also be 'Yes')
   Symmetric Media: No                  (may also be 'Yes')
   STUN Server:                         << n/a
   Request Period for STUN Server       << n/a
   Media Min Port: 7070                 << depend of siproxd config
   Media Max Port: 7080                    (RTP ports)

Q: If I update both inbound and outbound to
   if_inbound  = ppp0
   if_outbound = ppp0
   will this work ?

A: Very likely this will not work properly. Siproxd does masquerade User
   Agents hidden behind a NAT firewall (inbound network) so they can access
   other User Agents located in the public internet (outbound network).
   Therefore there MUST be 2 networks connected to the host running
   - Inbound network 
   - Outbound network

   If you just want a proxy located in the public IP range you should not
   use siproxd, but get a real SIP proxy server instead.

Q: I can build siproxd, but when I try to start it it fails with
   something like:
   $ siproxd -h
   siproxd: error while loading shared libraries:
   cannot open shared object file: No such file ordirectory

A: Make sure you have correctly installed libosip2. If libosip2 is
   installed somewhere else than the standard library paths, the
   path MUST be included in the /etc/ file to tell the
   dynamic linker where to search for libraries.
   Try the following command:
   $ /sbin/ldconfig -p|grep libosip
   The output MUST be something like: (libc6) => /usr/lib/ (libc6) => /usr/lib/ (libc6) => /usr/lib/ (libc6) => /usr/lib/

   If not, libosip2 is not correctly installed.