Enterasys Networks 700 - Manual (Page 159)

Configuring FDDI Frame Translation Settings 5-15
FDDI Management
Figure 5-8. The Frame Translation Window
Information about Ethernet and FDDI Frame Types
There are four frame types which can be transmitted on an IEEE 802.3/Ethernet
network – Ethernet II, Ethernet 802.2, Ethernet 802.3 (or Raw Ethernet), and
Ethernet SNAP
; there two frame types which can be transmitted on an FDDI
network: FDDI 802.2 and FDDI SNAP. Each of these frame types is described in
more detail in the sections that follow. Bridges connecting IEEE 802.3/Ethernet
LANs to an FDDI ring have to provide frame translation, as there are addressing
and frame format differences between the two network topology types.
For an Ethernet frame format to be forwarded onto an FDDI network, the Length
(IEEE 802/SNAP) or Type (Ethernet II) field must be removed (along with any
frame padding), an FDDI Frame Control field must be added, the bit-order of the
address fields must be reversed, and the frame’s CRC field must be recomputed.
In most instances, the IEEE 802.3/Ethernet frame format is translated
automatically into the appropriately corresponding FDDI frame format. Ethernet
802.2 frames are translated to FDDI 802.2 frames; Ethernet II frames are translated
to FDDI SNAP frames; non-AppleTalk Ethernet SNAP frames are translated to
FDDI SNAP frames; and AppleTalk Ethernet SNAP frames are translated to FDDI
SNAP frames (AppleTalk format).
However, because Ethernet Raw frames do not have a Type or Length field, and
can’t be automatically translated onto an FDDI network, you must select the
appropriate translation method to an FDDI frame format (for transmitting to
FDDI stations or for bridging back to an Ethernet network).