[openbeosnetteam] Re: header files
- From: "David Reid" <dreid@xxxxxxxxxxxx>
- To: <openbeosnetteam@xxxxxxxxxxxxx>
- Date: Sat, 9 Feb 2002 17:27:00 -0000
> >But is it correct that 1500 bytes is the maximum size=3D3F I often got
> >more, and IIRC the network card specs said something of 1536 or 1518.
> >We should just use the ether frame size returned by the driver and
> make
> >no assumptions about it (if it's in the area about 1500)=3D3F
>
> See http://www.cisco.com/warp/public/105/encheat.html. The spec is
> 1518 for Ethernet, which is 1500 for data, 12 for src and dst mac, 2
> for type and 4 for CRC =3D 1500+12+2+4=3D1518. So if you strip off the
> misc ethernet data, then the frame will be 1500 bytes max.
>
> Incidentally, there was a discussion earlier about whether it was 802.3
> or Ethernet. Ethernet has a "type" field and 802.3 has a "length"
> field. I did a bunch of packet captures on my network and it's all
> Ethernet with a type field for IP. IPX on the other hand can use any
> of 4 different frame types, but I doubt we'll ever mess with that.
yes, but 1518 / 16 = 94.875
1536 / 16 = 96
Some cards use 1536 as it's long word aligned is all. Why not 1520? 1536 /
256 = 6, so it's also easier to "fit" into page sizes as used by a lot of
systems...
david
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