Re: number of concurrent TCP sessions

[Kiss Karoly <crash () sunserv klamzi hu>]

On Tue, 24 Aug 2004, [iso-8859-1] César Cárdenas wrote:

> Dear all:
> In a captured file I found '.', S, F and FP flags...
> According to the manual:
>
> flag = '.' and data-seqno = '1' implies the first time tcpdump sees a TCP
> conversation.
>
> flag = 'S' and 'win (value)' stands for the beginning of a TCP conversation
>
> flag = 'F" implies FIN (end) and flag = 'FP' I guess implies Fin/Pushed
> (anyway end)
>
> I computed the number of concurrent TCP conversations throughout the time
> by adding a '1' each time I found a 'S' and substractin a '1' each time
> I found a 'F' or a 'FP'
>
> By doing this the number of concurrent TCP connections decreases linearly
> in a negative way through the time.
>
> Am I determining in a correct way the number of Concurrent TCP connections?
> I really appreciate if you could suggest me how to determine the number
> of concurrent TCP connections?
>
> Please accept mys best regards,
> Cesar Cardenas
>
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You forgot to mention the system you are using but if wou use linux and
have connection tracking enabled in the kernel ( module ip_conntrack )
then it's much easyer if you do a wc -l /proc/net/tcp
This will give you the number of connections pretty accurately.
But be careful with using ip_conntrack because it makes your box
vulnerable to SYN flood attacks.

Regards

Karoly Kiss
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