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[lwip-users] Re: how to change MTU

Subject: [lwip-users] Re: how to change MTU
Date: Thu, 21 Jan 2010 17:17:29 +0700

Dear Simon,

thanks for your explanation.

Currently, if my buffer size in application level set 1024 bytes then sending is successfully, but if i set it to 2048 i can not see it send any byte by wireshark. Below my message i got it when i send 2048-byte buffer.

Sending data...
tcp_write(pcb=4000a718, data="" len=1500, apiflags=1)
tcp_enqueue(pcb=4000a718, arg=400057a4, len=1500, flags=0, apiflags=1)
tcp_enqueue: queueing 6511:7971 (0x0)
tcp_enqueue: queueing 7971:8011 (0x0)
tcp_output_segment: 6511:7971

and program is hang if i send a array 10 items of buffer[2048]

I am using lwip-1.3.1.rc3 version.

please give me some idea.


On Thu, Jan 21, 2010 at 3:49 PM, PHAM ANH THIEN <address@hidden> wrote:
dear all,

i want to send a packet more than 1500 bytes, in my case is 2048 bytes, after sending i see the below message:

Sending data...
tcp_write(pcb=4000a718, data="" len=2048, apiflags=1)
tcp_enqueue(pcb=4000a718, arg=400057a4, len=2048, flags=0, apiflags=1)
tcp_enqueue: queueing 6511:7971 (0x0)
tcp_enqueue: queueing 7971:8559 (0x0)
tcp_output_segment: 6511:7971
   0:.tcp_write(pcb=4000a718, data="" len=952, apiflags=1)
tcp_enqueue(pcb=4000a718, arg=400057a4, len=952, flags=0, apiflags=1)
tcp_enqueue: queueing 8559:9511 (0x0)
tcp_output_segment: 7971:8559

this mean that i sent 2048 bytes successfully already, but when i use wireshark application (network analyzer application) i only see a packet with 588-byte length sent. I changed MTU (netif->mtu) from 1500 to 3000 and SND_BUF, TCP_MSS, TCP_SND_BUF, TCP_WND, ETH_FRAG_SIZE, ETH_MAX_FLEN from 1500 to 3000 as well.

Anyone know how to do it? please advise

thank you very much.

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