DeforaNetworks/siproxd
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siproxd/doc/FAQ
Thomas Ries 196e6efe6d - released 0.3.6 
- code cleanup for UDP masquerading tunnels
2003-09-22 20:33:16 +00:00

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Still under construction...
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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 (0.9.0)
- kphone (1.0.2)
- MSN Messenger
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Q: Siproxd's RTP proxying does only work for incoming RTP audio data.
Shouldn't italso proxy outgoing RTP data?
A: This is the correct behaviour. Incoming RTP traffic
is handled by siproxd's RTP proxy. However, outgoing RTP traffic has
to be handled by the firewall (IP masquerading).
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Q: How do I setup IP masquerading for the outgoing RTP traffic?
A: if you are using 'ipchains' it is a firewall rule like the following:
# ipchains -A forward -i ppp0 -j MASQ -s 10.0.0.0/24 -d 0.0.0.0/0
This will set up IP masquerading for all local hostx (10.x.x.x) to
the Internet (connected on ppp0). Read the ipchains documentation
for details.
More recent Linux Kernels (2.4.x) may use 'iptables' instead of
'ipchains'. Check the corresponding documentation for details
how to configure IP masquerading there.
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Q: Is it possible from a remote computer to call the inbound computer?
A: Yes, see also next question.
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Q: What SIP address must the remote computer use to make a call?
A: Scenario
--------
private IP address range : Internet
10.0.0.x : (publich IP address range)
:
: foo.bar.org xxx.org
+-------------+ +--------------+ +-------------+
! !.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 sip:johndoe@foo.bar.org
- The softphone on IntHost is configured to register at siproxd
running on the firewall host (10.0.0.1) as sip:johndoe@foo.bar.org
- foo.bar.org 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):
[sip]
sip_port=5060
use_registrar=1
username=johndoe
hostname=foo.bar.org
registrar=sip:10.0.0.1
reg_passwd=
addr_of_rec=sip:johndoe@foo.bar.org
reg_expires=900
as_proxy=1
as_redirect=0
as_outbound=1
To make an outgoing call from IntHost simply use the SIP address of the
target ( -> sip:test@xxx.org).
test@xxx.org can make a incoming calls - it simply has to use the registered
SIP address of the softphone running on IntHost (sip:johndoe@foo.bar.org).
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 sip:test@xxx.org it looks as he directly sends the traffic to
foo.bar.org, siproxd then takes care about where to send it from there.
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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 (sip:johndoe@foo.bar.org)
(lets call this address the 'masqueraded' or 'public' address)
- a 'Contact:' address of the *true* address (sip:johndoe@10.0.0.10)
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).
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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.
The above only applies for reception of data FROM the outbound
interface (usually a publich IP).
Outgoing traffic must be handled (masqueraded) by the firewall itself
(using ipchains or iptables rules).
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Q: Does siproxd need to be installed on the same host as the
firewall (ipchains/iptables) is running?
A: Yes. Siproxd needs to know the public IP address, as this address is
included in the SIP signalling to establish a session. However,
siproxd does *not* interact with ipchains/iptables. The requirement
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). Outgoing UDP packets must be masqueraded by the firewall.
See 'Q: How do I setup IP masquerading for the outgoing RTP traffic'.
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Q: How do I configure siproxd to use ICPHAINS based UDP masquerading
tunnels for proxying the incomming RTP traffic?
A: Simple. In the config file set the configuration option
rtp_proxy_enable = 2. Siproxd *must* then be started by root, I
highly recommend to let siproxd drop privileges after startup
(user, chrootjail config options).
Note: The UDP port range for incomming RTP data still uses the same
range as configured in the config file.
---------------------------------------------------------------------------
yet unstructured:
Hi there
As the maintainer of siproxd I may provide some useful informations ;-)
First I have to admin that the documentation of siproxd is
a) far from complete
b) not very detailed yet
c) could be better ;-)
For your enviroment the config of the linphone SIP parameters
would look like:
Your sip address: sip:rbrewer@<your_ppp_IP_address>
Server address: sip:192.168.0.1
Address of record: sip:rbrewer@<your_ppp_IP_address>
The following check boxes enabled:
- use sip registrar
- Proxy server
- Outbound Proxy
<your_ppp_IP_address> is the IP address (or host name) that you
got on the PPP link.
For siproxd, the outbound address will be <your_ppp_IP_address>.
Currently, you have two possibilities to use dynamic IP addresses
with siproxd:
a) Edit the config file each time you IP changes
I agree, this is not desirable
b) use some dynamic DNS service and then use the host name.
I personally use DynDNS (-> http://www.dyndns.org)
I may add some better support for dynamic IP addresses within
siproxd.
(has anybody some C code snipplets at hand how to fetch the IP
address of a specific interface by knowing just its name?)
Regards,
/Thomas
> Message: 3
> To: linphone-users@nongnu.org
> Date: Tue, 12 Nov 2002 01:38:04 -0500 (EST)
> Reply-To: rbrewer@op.net
> From: rbrewer@op.net (Robert W. Brewer)
> Subject: [Linphone-users]use with outbound proxy siproxd
>
> I'm running the Linphone 0.9.1 Debian package. It's working correctly
> as much as I've tested so far, which is just talking to sipomatic.
>
> Now I'm trying to operate with siproxd as an outbound proxy, since
> my Linphone machine connects to the Internet via another Linux box
> configured as an IP masquerading firewall.
>
> I've read the documentation, and it isn't very clear about
> what the different addresses mean. In particular, I'm
> confused about what to fill in for the following fields
> in the SIP Parameters tab:
>
> Your sip address: sip:rbrewer@wiz
> Server address: sip:192.168.0.1
> Address of record sip:rbrewer@192.168.0.1
>
> Do those look correct? Do they even matter since I'm not
> really registering with a server? Note that wiz is not a valid
> external DNS name. Linphone does seem to be registering with
> my siproxd.
>
> 192.168.0.1 is the internal address of my firewall machine
> 209.92.x.y is the external (ppp) address of my firewall machine,
> which is dynamic
> 192.168.0.10 is the internal address of my Linphone machine
>
> Also, it appears that every time I start my ppp session
> I will have to edit the siproxd config file and tell it
> my new outbound ppp address. Is that true?
>
> Thanks for any hints.
>
> -Rob
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