RE: [lwip-users] Jumbo frame questions

[Kieran Mansley]

On Tue, 2008-02-05 at 15:47 +0000, Kieran Mansley wrote:
> If that's correct, then you've got
> a configuration error: all nodes on the same LAN are supposed to have
> the same frame length and MTU, and it sounds like you've put the lwIP
> node with an MTU of 9000 on a network with an MTU of 1500.  That just
> doesn't work I'm afraid.

I've just had another look!  If you use the LWIP_CALCULATE_EFF_SEND_MSS
option and then set the MTU appropriately in your netif (the example
ethernetif.c just always sets it to 1500 - I presume your changes to get
jumbo frames working did something more sophisticated) you should be
able to safely set TCP_MSS to 8960 (i.e. an MTU of 9000) and lwIP will
downsize the MSS appropriately.

The bit that's probably missing in your port is the setting of netif-
>mtu.  This is normally configured using a tool like ifconfig on Linux,
but how you do this on your target will depend heavily on the OS (if
any) it's running.

Hope that helps,

Kieran