RE: [lwip-users] Lwip 1.3.0 Running out of TCP PCB's fast

[Pettinato, Jim]

This is due to pcbs being placed in a TIME_WAIT state; i.e. when you
close a connection they're not really freed yet, they're hanging around
waiting for enough time to pass to make sure no stray packets come in
and screw up a future connection. Note that the default 'enough time' is
like two hours, so an automatically refreshing web page will eat up pcbs
very quickly. (This is TCP standard behavior as defined in the RFQs,
though it makes little sense in today's high-speed networks.)

Even though the error count gets incremented, lwIP will (upon finding no
free pcbs) allocate a pcb from the TIME_WAIT list and use it, so this
may not actually be a problem for your implementation.


-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf
Of Jonathan Larmour
Sent: Wednesday, August 27, 2008 8:48 AM
To: Mailing list for lwIP users
Subject: Re: [lwip-users] Lwip 1.3.0 Running out of TCP PCB's fast

B B wrote:
> Now when i connect to the devices webpage, the number of used tcp_pcb 
> goes up.
> And after 10 page hits, the stats say the following:
>  
> TCP_PCB avail: 10
> TCP_PCB used: 10
> TCP_PCB max: 10
> TCP_PCB err: 5
> TCP_PCB_LISTEN avail: 3
> TCP_PCB_LISTEN used: 1
> TCP_PCB_LISTEN max: 1
> TCP_PCB_LISTEN err: 0
>  
>  
> i've thought that "TCP_PCB used" should be 2, one for each connection.
> But that is not the case.
> Is there anything i can do to avoid this situation ?
>  
> here is my code for my webserver task:
>  
[snip]
>  
> Should the above cause this behaviour ?

I didn't notice anything incorrect in what you posted. But does
handleDHCP() allocate any PCBs?

Jifl
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