Subject: [SIP] SIP through Firewalls Revisited

From: [email-masked]
Date: Sun, 4 Mar 2001 15:55:29 +0200

I saw the Feb 22 edition of "Getting SIP through Firewalls and NATs"
(draft-rosenberg-sip-firewalls.txt), with interesting updates on
draft-rosenberg-sip-entfw-001.txt.

With respect to the "Non-Solution 1", section 7,  page 27, you mention the
possibility that firewall implementors will learn "to block messages based
on their content" once they learn that we are doing this sort of thing.
Quite right. For example, firewalls nowadays can check the protocol to see
that it is really HTTP.

But just to be contrary, let me suggest if we want to implement this
non-proposal, with all its problems, and both sides of the SIP transaction
are cooperating, we could make the first token of the initial line
"HTTP/1.0" rather than "SIP/2.0".

 If we did that, it seems that SIP would be identical to HTTP as far as a
firewall is concerned. The HTTP protocol does not ban methods other than
GET, POST,  ...HEAD, and therefore INVITE, for example, should be legal for
HTTP.

Joshua Fox

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