Subject: Packet start alignment
To: None <tech-kern@NetBSD.ORG>
From: Bill Studenmund <>
List: tech-kern
Date: 11/14/1997 12:17:33
In talking with Denny about some netatalk changes, A question has
come up about routing packets from a phase 1 to a phase 2 net.

There are two AppleTalk link-level packet header schemes. One,
which was used on LocalTalk and EtherTalk phase 1, uses a
3-byte header in the data payload of the packet. The other, used
in EtherTalk Phase 2, uses an 8-byte LLC header.

When a packet is routed from a phase 1 net to a phase 2 net, the
data to be sent will begin on an odd byte boundry. The if_ethersubr.c
output code (We only support phase 2 nets on Ether right now) will
then M_PREPEND sizeof(struct llc) (8 bytes) to the packet and
fill in the llc header.

Will such a packet layout cause problems on any of our machines?
Or do they all hand copy the packet out, thus aleviating this

Take care,