Enterasys SmartSwitch 6000, User Manual

Page: 206 / 231

Configuring FDDI Frame Translation Settings 6-15
FDDI Management
Figure 6-8. 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).