Brocade Fabric OS Troubleshooting and Diagnostics Guide v6.2.0 (53-1001187-01, April 2009)

28 Fabric OS Troubleshooting and Diagnostics Guide

53-1001187-01

Marginal links

NOTE

If you are unable to read a portlog dump, contact your switch support provider for assistance.

Marginal links

A marginal link involves the connection between the switch and the edge device. Isolating the exact

cause of a marginal link involves analyzing and testing many of the components that make up the

link (including the switch port, switch SFP, cable, edge device, and edge device SFP).

Table 5 shows the different loopback modes you can use when using the portLoopbackTest to test

a marginal link.

Troubleshooting a marginal link

1. Enter the portErrShow command.

2. Determine whether there is a relatively high number of errors (such as CRC errors or ENC_OUT

errors), or if there are a steadily increasing number of errors to confirm a marginal link.

3. If you suspect a marginal link, isolate the areas by moving the suspected marginal port cable to

a different port on the switch. Reseating of SFPs may also cure marginal port problems.

If the problem stops or goes away, the switch port or the SFP is marginal (proceed to step 4)

If the problem does not stop or go away, see step 7.

4. Replace the SFP on the marginal port.

G_Port The port has not come up as an E_Port or F_Port. Check the output from portLogShow or

PortLogDump commands and identify the link initialization stage where the initialization

procedure went wrong.

L_Port If the opposite side is not a loop device, the link has come up in a wrong mode. Check the

output from portLogShow or PortLogDump commands and identify the link initialization

stage where the initialization procedure went wrong.

TABLE 4 SwitchShow output and suggested action (Continued)

Output Suggested action

TABLE 5 Loopback modes

Loopback mode Description

1 Port Loopback (loopback plugs)

2 External Serializer/Deserializer (SerDes) loopback

5 Internal (parallel) loopback (indicates no external equipment)

7 Back-end bypass and port loopback

8 Back-end bypass and SerDes loopback

9 Back-end bypass and internal loopback