Thanks Jiri,

I'll have a look at the CVS version. I'm sure there will be more hacking to do only to make it compile.... :(

However, got the replacement of the "c=.." part working. I'll test this as soon as I can.

Jaime

Jiri Kuthan jiri@iptel.org on 24/02/2003 13:20:00

To: Jaime GILL/EN/HTLUK@HTLUK Nils Ohlmeier nils@ohlmeier.de cc: Jan Janak J.Janak@sh.cvut.cz serusers@lists.iptel.org

Subject: Re: [Serusers] FCP support in SER: Modifying SDP

At 12:50 PM 2/24/2003, jaime.gill@orange.co.uk wrote: [...]

It think the problem is in the replacement of the SDP information. The first occurrence of the IP address in "v= " and the port in "m= " in the SDP get replaced, but the second IP in "c=" is not.

nit: it's not the "v=" line, but "o=" ('owner') line which you are replacing. However, you are not probably worried so much about this one -- it maintains primarily a (not widely utilizied) identification purpose. All "c=" occurences do matter. (In addition to port numbers in "m=" lines.)

[...]

I have been trying to understand how the proxy builds the forwarded message

from

the old one, and realised that for the Via replacement (or adding of more params), I need to be using a string called add_to_branch_s and add_to_branch_len (so ignore the replace_via implementation in the current tar.gz).

I suggest you used the mhomed option (available only on CVS). The issue is you need to print the correct IP address in Via on multihomed host. With mhomed enabled, IP routing is utilized to determine the right IP address. Let me know if you need something more for getting Via right.

But for the SDP, whenever I work with get_body, it does not modify it appropriately. So currently, I'm using msg->orig to get to the initial message, search for certain IP4 and audio strings and replace them with the information provided by the fcp server. That means, in the case of the SDP, 2 IP address replacements (in v=.. and c=..) and 1 port replacement (in m=..). As I

mentioned

before, I only manged to change the v=.. and m=... Whenever I try to replace more than one appearance, strange things happen, like strings in non expected places, like Via, and cannot work out why. So my question is an open one:):

what

is the best way to change the SDP part?

I suggest here too -- use the CVS version. It has departed from the use of the buffers (orig and buf) -- we have now just one buffer (buf) without any zero termination. Previously, the two buffers and 0-termination caused lot of issues, some of them possibly annoying you right now. Look at the textops/replace_all action (only on CVS too) to see how to replace multiple occurences of a string in SIP messages. (Caution: you will eventually need to calculate new SDP body size and change content-length too.)

The other of my questions is whether all this mess with NAT's will get solved when the proxy supports TCP,

The major problem is media, which will keep using UDP.

and whether this is the best approach to solve the SIP through NAT/FW problem.

As all NAT traversal methods -- none of them is perfect, each has cons and pros. The benefit of FCP is that once fcpd works, maintenance of the SIP code is easier in user space. Also, you can better couple your pinhole policy with SER's SIP-layer policy.

For example, how about a nathelper module for netfilter/iptables that gets this working, in the same manner as IRC or ftp currently? Does anybody know about any work progressing this for linux/FreeBSD?

I'm not aware of such. There is Billy Biggs masquerading module, but it is pretty old and no longer maintained.

-Jiri

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