30 Jul
2004
30 Jul
'04
5:45 a.m.
At 11:40 PM 7/29/2004, Andres wrote:
We have started having problems with customers in
BellSouths ADSL network. New customers are being given the Westell ADSL modem which
appears to be "SIP Aware". But the implementation is terribly broken.
Well, I think that Application-Level-Gateways (ALGs) is _fundamentally_ broken
concept with very negative impact on interoperability, security and software
engineering.
There will be attempt to create an effort documenting these issues in the upcoming
IETF meeting; till this effort brings fruits it will take some time. Some enlighted
vendors are aware of this: Cisco/Linksys gave up on the idea to introduce SIP
awareness in residential routers.
Thank you for your report.
-jiri
The symptoms are that SIP INVITES cannot penetrate the
NAT on the Modem even though we have a permanent Keep-Alive from the inside (every 15
seconds). Furthermore when the customer tries to make a call, the modem changes the
source port of every single packet of the dialog. Thus breaking the SIP dialog
completely.
Our interim solution was to setup these customer on an alternate server listening on a
different port.
For everybody's reference the modem version is: Westell B9061003006 and the Software
is: 03.00.61
I have tried to contact Westell directly but they have not answered. I hope this is not
something thats going to start happening with all modem manufacturers or else were going
to have loads of trouble.
--
Andres
Network Admin
http://www.telesip.net
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--
Jiri Kuthan http://iptel.org/~jiri/