Filter
Top Products
Configuring FDDI Frame Translation Settings 6-17
FDDI Applications
FDDI Frames
There are two legal FDDI data frame types:
FDDI 802.2
The FDDI 802.2 frame type has two headers: the FDDI header (which includes the
Frame Control Þeld that indicates the class of frame, length of the address Þeld,
and the type of FDDI frame), and the 802.2 header.
FDDI SNAP
The FDDI SNAP frame type has an FDDI header with a Frame Control Þeld that
provides FDDI framing information, and the 802.2 LLC header with FDDI Frame
Control, a SNAP LSAP identiÞer, and a Þve byte protocol identiÞer.
There is no FDDI equivalent for Ethernet 802.3 Raw frames or Ethernet II frames.
CabletronÕs Ethernet/FDDI bridges will automatically translate Ethernet II
frames into FDDI SNAP frames, by identifying it as a SNAP frame in the LLC
header, and inserting a SNAP header with the Ethernet Type Þeld.
By default, CabletronÕs Ethernet-to- FDDI bridges will translate an 802.3 Raw
frame into an FDDI MAC frame Ð although you can use the FDDI Frame
Translation window to alter the default translation. The FDDI MAC frame is an
FDDI frame type that is deÞned for internal use by the MAC layer, and which is
not passed to higher layer communications protocols on the datalink layer. Any
802.3 Raw frame translated into FDDI MAC will be recognized as such by other
Cabletron (and many other vendorÕs) Ethernet/FDDI bridges inserted in the ring,
and will be forwarded onto the target Ethernet segment as an 802.3 Raw frame.
FDDI Frame Translation Options
The FDDI Translation window lets you select which translation methods you
want enforced when translating frames from an FDDI frame format into an
Ethernet frame format, and when translating Ethernet Raw frames into FDDI
frames. It also lets you choose whether to allow fragmentation of IP datagrams
into smaller datagrams, and enable or disable the Auto Learn Novell Frame
Translation option.
To set frame translation parameters:
1. Click on the selection boxes of interest (described below), and select the
desired translation options.
2. Click Apply to save your new frame translation settings at the device, or click
Cancel to restore the last saved options.
IP Fragmentation
The IP Fragmentation selection box lets you specify frame fragmentation
parameters. FDDI trafÞc may need to be split, or fragmented, into two, three, or
four smaller frames to be successfully transmitted on an Ethernet network. For
fragmentation to be allowed, the frame must be an FDDI SNAP frame with an