Physical Configuration Restrictions; Required Network Preparation - Frame Length Limit - Olicom CrossFire 8730 Installation Manual

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Physical Configuration Restrictions

This section contains information about the physical configuration restrictions for
the switch. In brief, you must remember the following rules when planning to
install the switch:
•
For shared-media LAN segments, acceptable distances are defined by the hub
or concentrator attached to the switch port.
•
If you create parallel paths directly between switches, be sure that you have
enabled the spanning tree protocol (see
the
CrossFire 8730 Fast Ethernet Translation Switch—Reference Guide
default setting for the spanning tree protocol is disabled.
•
The spanning tree protocol will not function between different BRFs within
one switch.
The following sections provide greater detail about the physical restrictions.

Required Network Preparation - Frame Length Limit

The CrossFire 8730 Switch supports a maximum physical frame length of 18,192
bytes on Token-Ring ports (from the Frame Control (FC) to the Frame Check
Sequence (FCS) characters). This corresponds to a Maximum Transfer Unit (MTU)
of 17,800 bytes.
The default maximum physical frame length for Token-Ring ports is 4,546 bytes
which corresponds to an MTU of 4,472 bytes. The actual MTU size of a VLAN is
configured in the
CrossFire 8730 Fast Ethernet Translation Switch—Reference Guide .
The switch truncates Token-Ring frames larger than the configured maximum
physical frame length and adds an abort sequence at the end. Characteristically, if
frames longer than the frame length limit are sent, the abort sequences will be
reported as frame errors by other ring stations.
In a stack of switches, all stacker link modules in the stack must support 18,192
byte frames (18 K frames) for any switch in the stack to support Token-Ring frames
sizes longer than 4,546 bytes.
To verify that your hardware supports 18 K frames, view the
screen, described in the
Reference Guide
the text (4k) displayed immediately after the hardware revision level.
For information on how to upgrade your stacker link modules that currently do not
support 18 K frames, please contact your local Olicom representative.
Note: It is most important that you consider the impact of the frame length limit,
CrossFire 8730 Switch Installation Guide, DOC-7046 v. 1.2
VLAN Parameter Configuration for TrBRF
CrossFire 8730 Fast Ethernet Translation Switch—
. Stacker link modules that do not support 18 K frames will have
"Spanning Tree for TrBRF Screen"
Module Information
in
). The
screen, see the
Preparing for Installation