[Freeswitch-users] TCP ACK Ping

[Spencer Thomason]

Understood, I though it was quite strange to see these unsolicited ACKs 
from the Polycoms followed by a RST.

Thanks,
Spencer


On 05/13/2013 02:07 PM, Steven Schoch wrote:
> On Sun, May 12, 2013 at 2:54 PM, Spencer Thomason 
> <spencer at 5ninesolutions.com <mailto: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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