skl@van-bc.wimsey.bc.ca (Samuel Lam) (09/21/90)
In article <1410@alfred.tegra.COM>, cooper@tegra.UUCP (Al Cooper) wrote:
)It seems that the Phase 2 packets are in 802.2 format
)instead of normal Ethernet format used by Phase I and TCP/IP. The 802.2
)header differs in that instead of a protocol type following the
)destination and source addresses there is a byte count. If this is
)all true, does that mean that there is no way to differentiate the
)two formats, and therefore no way to run both TCP/IP and Ethertalk
)at the same time?
The way to separate the Ethernet and IEEE 802.3 packets on the wire
is to look at the 13rd and 14th octet of the packet (the Ethertype/
802.3-length field). If this value is less than 0x0600 it's an Ethernet
packet, otherwise it's an IEEE 802.3 packet.
...Sam
--
Internet: <skl@wimsey.bc.ca> UUCP: {van-bc,ubc-cs,uunet}!wimsey.bc.ca!sklwinders@aux.support.apple.com (Scott Winders) (09/22/90)
EtherTalk 2.x (802.3) Frame
802.3 Destination 6 bytes
802.3 Source 6 bytes
802.2 LLC Length 2 bytes
802.2 LLC Header
802.2 LLC DSAP 1 bytes (always $AA (SNAP SAP) for EtherTalk 2.x)
802.2 LLC SSAP 1 bytes (always $AA (SNAP SAP) for EtherTalk 2.x)
802.2 LLC Control 1 bytes (always $03)
SNAP Header 5 bytes (always $080007809B for EtherTalk 2.x)
DDP Header 13 bytes
AppleTalk Data ?? bytes (586 bytes maximum)
Padding (if needed) ?? bytes
---------------
60 to 621 bytes
DSAP - Destination Service Access Point
SSAP - Source Service Access Point
The SNAP SAP is defined as $AA
A SNAP address has been defined by the IEEE for AARP packets.
The SNAP number is $00000080F3.
Scott Winders
internet: winders@aux.support.apple.com
AppleLink: winders.s@applelink.apple.com