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Re: [lwip-users] Understanding MTU and Max ETH Frame size
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From: |
Simon Goldschmidt |
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Subject: |
Re: [lwip-users] Understanding MTU and Max ETH Frame size |
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Date: |
Tue, 28 May 2013 08:53:56 +0200 (CEST) |
Dimax wrote:
> To define driver strategy I want to better understand what can be a Max
> Ethernet Frame size that driver can receive
> from MAC?
> If I get it right I should not get packets longer then MTU ?
> Am I right?
> If yes why I do not see MTU configuration in lwipopts.h ? All I can see is
> /* TCP Maximum segment size. */
> #define TCP_MSS (1500 - 40)
> Does it mean that MTU=1500 is hardcoded value?
No. MTU is a member of struct netif and must be set per netif in its init
function. For standard ethernet, this *is* 1500 (so a complete ethernet frame
including headers is 1514 bytes long at maximum). You might be able to
send/receive longer frames in your local subnet, though.
Simon