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vertigo 06-28-2006 03:30 PM

P flag
 

Hello

What is P (Push) flag in TCP used in real life ?
Could cisco block such packets somehow ?

Thanx
Michal

ciscodagama@gmail.com 06-30-2006 12:27 AM

Re: P flag
 
> What is P (Push) flag in TCP used in real life ?
> Could cisco block such packets somehow ?


To see how the filtering with ACLs based on TCP flags might be done,
take a
look at

http://www.cisco.com/en/US/products/...0801d344e.html

Cisco da Gama
http://ciscostudy.blogspot.com


SAto 06-30-2006 08:43 AM

Re: P flag
 
vertigo skrev:
> Hello
>
> What is P (Push) flag in TCP used in real life ?
> Could cisco block such packets somehow ?


Normally a TCP host is allowed to buffer data.
The TCP push flag forces it to hand the data over to upper level
applications right away insted of buffering it. (it is still allowed to
delay acknowledgements though.)

This is from the RFC:
---
A sending TCP is allowed to collect data from the sending user and to
send that data in segments at its own convenience, until the push
function is signaled, then it must send all unsent data. When a
receiving TCP sees the PUSH flag, it must not wait for more data from
the sending TCP before passing the data to the receiving process.
---

Citrix and RDP for example use this to update the client.

-SAto



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