[Freeswitch-users] TCP ACK Ping

[Steven Schoch]

On Sun, May 12, 2013 at 2:54 PM, Spencer Thomason <
spencer at 5ninesolutions.com> wrote:

> The phones periodically send a TCP ACK ping to
> Freeswitch which goes unanswered and then phone then tears down the TCP
> connection.  I'm not at all a TCP expert but should Freeswitch be
> responding to this unsolicited ACK?


I've been working with TCP for 25 years, and this is the first I have heard
of ACK ping. A quick Google search told me that this technique involves
sending a normal TCP ACK packet (which all TCP packets except the initial
one have, by the way) to a random TCP port. The host will then respond with
a RST packet. (Which means reset the connection because the ACK was not
sent to an established connection.)

However, a firewall may filter and discard these random ACK packets. Since
they're not part of "normal" TCP, no one cares.

In answer to your question, this is in the TCP layer much deeper than
Freeswitch. There is nothing Freeswitch can do at this level.

-- 
Steve
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