[VOIPSEC] TLS and Firewalls
Brian Rosen
br at brianrosen.net
Thu Feb 10 12:46:03 CST 2005
It's possible to make the firewall a proxy server, but then it couldn't
modify a lot of the headers. That may be okay. Remember that there really
isn't a precise definition of a B2BUA other than it appears to be a User
Agent to both sides. You can make them appear to be transparent to both
ends. Proxy servers, if you follow the rules, are visible. If the firewall
was a proxy server, it would have to add a VIA header, for example. To be
really picky, you really would have to make the firewall-as-proxy-server BE
in the path. That means it has an address, and the routing mechanisms cause
the SIP messages to be sent to it. Again, that may be okay for some.
Brian
> -----Original Message-----
> From: Voipsec-bounces at voipsa.org [mailto:Voipsec-bounces at voipsa.org] On
> Behalf Of Per Cederqvist
> Sent: Thursday, February 10, 2005 12:35 PM
> To: Thomas Howe
> Cc: Voipsec at voipsa.org
> Subject: Re: [VOIPSEC] TLS and Firewalls
>
> The firewall does not have to be a B2BUA. Please remember that TLS is
> used hop-by-hop in SIP. It is enough that the firewall contains a SIP
> server with support for TLS, and that it arranges to stay in the
> signaling path. That way, the firewall will also be able to look
> inside the SDP to figure out what ports to open for the media streams.
>
> Yours,
> Per Cederqvist
>
> "Thomas Howe" <howethomas at aol.com> wrote:
>
> > Hi Michael -
> >
> > Yes, you are certainly right on that point. It is very useful to look
> > at real world practice when working on the standards. I have to side
> > with Brian though, and feel that as cumbersome as the standards bodies
> > are, they are the only real way to solve the long term problem. And more
> > than that, they have clearly identified SIP as the protocol for handling
> > session management, and the industry is cleary behind it now.
> >
> > Here's my question about SIP, firewalls and architectures - please tell
> > me where I'm right/wrong/inbetween....
> >
> > Given that SIP signalling uses TLS for security, doesn't that sort of
> > imply that most firewalls will be using some sort of back to back user
> > agent, instead of packet inspection? I mean, how will the firewall be
> > able to decrypt the streams appropriately without being a terminating
> > point for the call?
> >
> > Tom
> >
> >
> >
> > Michael Sandee wrote on 2/9/2005, 4:28 PM:
> >
> > > Hi Thomas,
> > >
> > > I accept your comments in general, however they are not true for IAX.
> > > But I know this is nearly impossible to know without looking at the
> > > protocol in detail. Dispite earlier comment a RFC is still in the
> works,
> > > and given the dozen of standards and extensions of earlier VoIP
> > > protocols it might be better to first analyse a protocol in
> _practice_
> > > before filing it as RFC.
> > >
> > > Ein Reich, Ein Protocol... or "One Protocol to rule them all"... I
> think
> > > we are not looking at IAX as a replacement of any existing protocol,
> but
> > > it has, as earlier pointed out, clear advantages over other protocols
> to
> > > deal with _current_ problems.
> > >
> > > The IAX protocol has a mechanism to hand off calls between 2
> endpoints,
> > > but this can be disabled on a call by call basis. Two endpoints
> behind
> > > NAT naturally cannot communicate with each other in a direct path, so
> > > this will proceed through a central/public gateway (This is usually
> only
> > > an issue with Internet Telephony, or very large Internetworks).
> > >
> > > For scalability this is ideal, because the entire call can be
> offloaded
> > > to a different server, perhaps after authentication to one of the
> > > frontends. In relation to SIP this can be done for the control
> channel
> > > by using 302 Moved signalling, possibly a similar mechanism exists
> for
> > > H323.
> > >
> > > Billing between VoIP/IP endpoints is something which is not important
> > > (for us). These are free calls and only interesting for statistics.
> > > However there is an extension to the protocol to actually handle
> this.
> > >
> > > Billing is usually done on the PSTN gateways.
> > >
> > > Regarding the security relation this might be interesting:
> > > Given that you cannot do billing on your speech detection system,
> IVR,
> > > or whatever.
> > > Given that it is a blackbox speech processor.
> > > Would you expose it to a direct media path to the user?
> > >
> > > [IAX ENDPOINT] - IP Network - [IAX GATEWAY] - SIP/H323/MGCP/SCCP/IAX
> -
> > > [BACKEND SPEECH PROCESSING]
> > > You will have a frontend either way, but it might be your security
> rules
> > > are different than mine.
> > >
> > > Regards,
> > >
> > > Michael
> > >
> > > Thomas Howe wrote:
> > >
> > > >Michael -
> > > >
> > > >Let me weigh in on that one. A single port for transport has some
> > > >serious scaling and implementation issues. A single port makes an
> > > >assumption that the media and control signalling are both going to
> the
> > > >same place. Maybe that might be an OK assumption for an IP phone,
> but
> > > >what about any large scale device? Would you really have all the
> media
> > > >flow through the control processor, then out again into the media
> > > >processor? That becomes very cumbersome, very quickly.
> > > >
> > > >It also has a problem with disaggregation. If you wanted to add an
> > > >speech detection system into your network, how would that work?
> Would
> > > >you put one into every IP phone? Or maybe you could come up with a
> call
> > > >control scheme that would hand off the call to another system.
> Well, if
> > > >you completely handed off the call, how would you do billing and
> > > >authorization? Or, if you didn't, can you imagine the convoluted
> call
> > > >control ladders to get that done? And if you could, then try to
> scale
> > > >that puppy, and you could get a discount price on Tylonol for your
> > > >headache.
> > > >
> > > >It would be so much simpler to send the RTP somewhere else for a
> while,
> > > >thus requiring a separate port for it. (Of course, two if you count
> > > RTCP).
> > > >
> > > >This help any?
> > > >
> > > >Tom
> > > >
> > > >
> > > >
> > > >Michael Sandee wrote on 2/9/2005, 2:15 PM:
> > > >
> > > > > Brian,
> > > > >
> > > > > RTP and the problems surrounding firewalls, NAT/PAT have been
> > > around for
> > > > > quite a few years, being it H323, SIP or...
> > > > > Trying to globally solve this is a nice goal to set, but
> > > (apparently)
> > > > > impossible to accomplish. There are workarounds like STUN which
> work
> > > > > with _some_ devices.
> > > > >
> > > > > If one protocol comes forward which has some distinct advantages
> > > over
> > > > > the alternatives, it cannot be considered a "Not Invented Here"
> > > > > protocol. The advantages are not only a single port, but also
> > > trunking
> > > > > and some other features which are very useful in a practical pbx
> > > > > environment.
> > > > >
> > > > > Can you please elaborate on why exactly IAX is bad for choosing
> a
> > > single
> > > > > port as transport?
> > > > >
> > > > > Michael
> > > > >
> > > > > Brian Rosen wrote:
> > > > >
> > > > > >Ultimately, this is the problem with IAX. It's a special
> protocol,
> > > > > >promulgated by a small group, without a rigorous process.
> > > > > >
> > > > > >It's not in the general interest of the Internet Community
> > > (whatever
> > > > > that
> > > > > >is) to have multiple ways to do the same thing. SIP is the way
> the
> > > >IETF
> > > > > >decided to do session management, including voice, video and
> text
> > > > > (although
> > > > > >there are other IM protocols). IETF is not the only game in
> > > town, of
> > > > > >course.
> > > > > >
> > > > > >I think that, actually, the IAX one port idea is a bad way to
> > > handle
> > > > > >signaling and multiple media streams related to the same
> session.
> > > > > The fact
> > > > > >that it makes it easier on the firewalls is not enough to
> > > overcome the
> > > > > >limitations it has. We're better off working to make SIP and
> > > > > firewalls work
> > > > > >better together.
> > > > > >
> > > > > >Brian
> > > > > >
> > > > > >
> > > > > >
> > > > > >>-----Original Message-----
> > > > > >>From: Voipsec-bounces at voipsa.org
> > > >[mailto:Voipsec-bounces at voipsa.org] On
> > > > > >>Behalf Of Diana Cionoiu
> > > > > >>Sent: Wednesday, February 09, 2005 12:09 PM
> > > > > >>To: Alexander
> > > > > >>Cc: Voipsec at voipsa.org
> > > > > >>Subject: Re: [VOIPSEC] TLS and Firewalls
> > > > > >>
> > > > > >>If you find any RFC avaibile for IAX let me know. Until now we
> > > have
> > > > > >>implement IAX based on what we have been able to learn from
> other
> > > > > people
> > > > > >>code. The problem with IAX secure is that of course there is
> no
> > > > > standard
> > > > > >>and we have to get all developers from different projects
> > > together and
> > > > > >>"maybe" we are lucky enough to convince them to make it work
> > > right.
> > > > > >>>From my experience each project has his own IAX version.
> > > > > >>
> > > > > >>Diana
> > > > > >>
> > > > > >>
> > > > > >>
> > > > > >>>>one port. The problem with IAX is that are no devices
> around. We
> > > >hope
> > > > > >>>>
> > > > > >>>>
> > > > > >>that
> > > > > >>
> > > > > >>
> > > > > >>> There are some devices with IAX support, and the trend is,
> > > there
> > > > > >>> will be more soon. Just few of them:
> > > > > >>>
> > > > > >>> http://www.iaxtalk.com/
> > > > > >>> http://www.digium.com/index.php?menu=iaxy
> > > > > >>> http://www.farfon.com/
> > > > > >>>
> > > > > >>>Regards,
> > > > > >>>/Al
> > > > > >>>
> > > > > >>>_______________________________________________
> > > > > >>>Voipsec mailing list
> > > > > >>>Voipsec at voipsa.org
> > > > > >>>http://voipsa.org/mailman/listinfo/voipsec_voipsa.org
> > > > > >>>
> > > > > >>>
> > > > > >>_______________________________________________
> > > > > >>Voipsec mailing list
> > > > > >>Voipsec at voipsa.org
> > > > > >>http://voipsa.org/mailman/listinfo/voipsec_voipsa.org
> > > > > >>
> > > > > >>
> > > > > >>
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >_______________________________________________
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> > > > > >Voipsec at voipsa.org
> > > > > >http://voipsa.org/mailman/listinfo/voipsec_voipsa.org
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > > _______________________________________________
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> > > >
> > > >
> > > >
> > > >
> > > >
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> > > >http://voipsa.org/mailman/listinfo/voipsec_voipsa.org
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> > > >
> >
> >
> >
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