BCE on FreeBSD and oversized packet acceptance.

[Julian Elischer]

more on this issue:

802.3-2000 expanded the maximum frame size for standard ethernet to 1522
bytes (including vlan header, ethernet header and CRC). however this has produced
quite a bit of confusion with HP telling their custommers to set their MTUs
on equipment to 1522, which in turn has packets of 1522+vlan_header+CRC+etherhedr
(i.e. too big) floating around some networks. When we try to connect our FreeBSD
based products on these networks thigns go badly. Sure they've misconfigured
their networks but telling a bank to reconfigure their network with all the
change-control they have, is a sure fire way to lose a $100,000 deal.

Our action has been to relax the discard limit on various drivers, but
it'd be nice if we didn't have to keep separate diffs for this.

I discussed it a while back on net but the discussion was mostly
about the code in if_ethersubr.c (since deleted) that did the same.

I'd like to just ask around as to whether relaxing the limit on drivers
makes sense, and if so, how much to relax it.  While we're about it,
what size is the actual maximal sized jumbo packet we will ever see? (including
likely misconfigurations).

It is possible we should just allow any packet that fits into the allocated memory,
though one might suggest we just allow say 32 bytes of leeway or something.



Julian