Subject: [Ietf-behave] Fwd: [Serusers] Broken "SIP Aware" Router

From: Jiri Kuthan <[email-masked]>
Date: Fri, 30 Jul 2004 18:45:05 -0700 (PDT)

FYI: here is a real-world testimony which imho captures deployment
issues with ALGs and which was reported by a SIP provider on
some of iptel's mailing lists.

Whereas this is just a single report, we experienced similar issues with 
other similar products too. I don't think these problems have to do with 
a young implementation -- I believe they are caused inherently by ALG design. 
IMHO ALGs are  prone to all kind of errors: interoperability (ALGs are likely 
to miss some novel application aspects), security (ALGs can't handle secured 
traffic) and generally software-engineering (i.e., increased complexity,
difficult troubleshooting, taking care of firmware upgrades).

-jiri

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We have started having problems with customers in ********'s ADSL 
network.  New customers are being given the +++++++'s ADSL modem which 
appears to be "SIP Aware".  But the implementation is terribly broken.

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:  ++++++++ ----------- and 
the Software is: 03.00.61

I have tried to contact +++++++++ 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.