Reference Guide

Long-distance link modes
Use the portCfgLongDistance command to support long-distance links and to allocate sufficient numbers of full-size frame buffers on a
specific port. Changes made by this command are persistent across switch reboots and power cycles.
The portCfgLongDistance command supports the following long-distance link modes:
∙ Normal Mode (L0) — L0 is the normal (default) mode for an E_Port. It configures the E_Port as a standard (not long-distance)
ISL. A total of 20 full-size frame buffers are reserved for data traffic, regardless of the E_Port’s operating speed. The maximum
supported link distance is up to 5 km at 2 Gbps, up to 2 km at 4 Gbps, and up to 1 km at 8, 10, and 16 Gbps.
∙ Extended Mode (LE) — LE configures the distance for an E_Port when that distance is greater than 5 km and up to 10 km. LE
does not require an Extended Fabrics license. The baseline for the buffer credit calculation is one buffer credit per km at 2
Gbps. This allocation yields the following values for 10 km:
– 10 buffer credits per port at 2 Gbps
– 20 buffer credits per port at 4 Gbps
– 40 buffer credits per port at 8 Gbps
– 50 buffer credits per port at 10 Gbps
– 80 buffer credits per port at 16 Gbps
– 160 buffer credits per port at 32 Gbps
∙ Dynamic Mode (LD) — LD calculates buffer credits based on the distance measured during port initialization. Brocade switches
use a proprietary algorithm to estimate distance across an ISL. The estimated distance is used to determine the buffer credits
required in LD (dynamic) extended link mode based on a maximum Fibre Channel payload size of 2,112 bytes. You can place an
upper limit on the calculation by providing a desired_distance value. Fabric OS confines user entries to no larger than what it
has estimated the distance to be. When the measured distance is more than the specified desired distance, the desired distance
(the smaller value) is used in the calculation.
∙ Static Mode (LS) — LS calculates a static number of buffer credits based only on a user-defined desired_distance value. LS
mode also assumes that all FC payloads are 2,112 bytes. Specify LS mode to configure a static long-distance link with a fixed
buffer allocation greater than 10 km.
Configuring an extended ISL
Before configuring an extended ISL, ensure that the following conditions are met:
∙ The ports on both ends of the ISL are operating at the same port speed, and can be configured for the same distance_level
without compromising local switch performance.
NOTE
A long-distance link also can be configured to be part of a trunk group. Two or more long-distance links in a port group form a
trunk group when they are configured for the same speed and distance, and their link distances are nearly equal. For
information on trunking concepts and configurations, refer to Managing Trunking Connections on page 467.
∙ Only qualified Brocade SFP transceivers are used. Only Brocade-branded or certain Brocade-qualified SFP transceivers are
supported.
1. Connect to the switch and log in using an account assigned to the admin role.
2. Enter the switchDisable command.
3. Enter the configure command to set the switch fabric-wide configurations.
Table 92 shows the fabric-wide settings that can be set:
Managing Long-Distance Fabrics
Brocade Fabric OS Administration Guide, 8.0.1
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