RE: [lwip-users] Jumbo frame questions

[Bill Auerbach]

Thanks,
 
Bill Auerbach
 

> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On Behalf
> Of Kieran Mansley
> Sent: Tuesday, February 05, 2008 11:01 AM
> To: Mailing list for lwIP users
> Subject: RE: [lwip-users] Jumbo frame questions
> 
> 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.

I do (or have left) this option enabled.  My issue was setting MTU to the
packet size.  I'm surprised I've gotten as far as I have. :)

> 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.

I wasn't adjusting MTU (or MSS) for the headers.  I am able to leave the
lwIP stack and it's controller set for Jumbo frames and it does communicate
on a network not supporting it.  This was what I was after - and maybe it
works *only* with my router?  lwIP was crashing this way because of the MTU.

Thank you for your help and replies.  I didn't mean for you to expend so
much effort but it helped me.    I can't explain the jumbo and non-jumbo mix
working.

Bill