Layer 1 Issues archives - Network technologies and trends

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Layer 1 issues

Aug 30 2008   5:16AM GMT

A cool tool to solve layer 1 UTP cable issues in Cisco Catalyst Switches.



Posted by: Yasir Irfan
Switches, Cisco, Cisco Tips, Cisco 3560, Cisco Learning, Cisco 3750-E, Cisco 3560-E, Network Troubleshooting, IOS commands, Layer 1 issues

Here is a simple and cool tool for solving layer 1 UTP cable issues in a Cisco Catalyst Switches, the command used for this function is “test cable-diagnostics tdr interface”
Here is the example

MBGF-DAC-3560-AS01#test cable-diagnostics tdr interface gigabitEthernet 0/1
TDR test started on interface Gi0/1
A TDR test can take a few seconds to run on an interface
Use ’show cable-diagnostics tdr’ to read the TDR results.
MBGF-DAC-3560-AS01#
The Catalyst 2960, 2970, 3560/3560-E, and 3750/3750-E switches have an integrated Time Domain Reflector (TDR), which is used to test cables associated with a port. TDR is supported only on 10/100/1000 and some 10/100 (Catalyst 2960) copper Ethernet ports. It is not supported on 10 GigabitEthernet or SFP module ports.

A TDR test can take a few seconds to run on an interface. Use “show cable-diagnostics tdr” to read the TDR results.

MBGF-DAC-3560-AS01#sho cable-diagnostics tdr interface gigabitEthernet 0/1
TDR test last run on: August 30 08:01:35

Interface Speed Local pair Pair length        Remote pair Pair status
——— —– ———- —————— ———– ——————–
Gi0/1     1000M Pair A     54   +/- 4  meters Pair A      Normal             
                Pair B     52   +/- 4  meters Pair B      Normal             
                Pair C     53   +/- 4  meters Pair C      Normal             
                Pair D     54   +/- 4  meters Pair D      Normal             
MBGF-DAC-3560-AS01#

Aug 17 2008   5:55AM GMT

What is the Link-flap error in Cisco Switches?



Posted by: Yasir Irfan
Switches, Cisco, Cisco 2950, Cisco 6500, Cisco 3560, Cisco 3750-E, Cisco 3560-E, Link-Flap, Err-disable, Layer 1 issues

Link flap means that the interface continually goes up and down in a Cisco Switch. The interface is put into the errdisabled state if it flaps more than five times in 10 seconds. The common cause of link flap is a Layer 1 issue such as a bad cable, duplex mismatch, or bad Gigabit Interface Converter (GBIC) card. Look at the console messages or the messages that were sent to the syslog server that state the reason for the port shutdown.

13w0d: %PM-4-ERR_DISABLE: link-flap error detected on Fa0/28, putting Fa0/28 in err-disable state 

Issue this command in order to view the flap values:

SRCL-ONC-3550-AS01# sho errdisable flap-values  ErrDisable Reason    Flaps     Time (sec)

—————–        ——   ———-

pagp-flap                        3       30

dtp-flap                           3       30

link-flap                           5       10

SRCL-ONC-3550-AS01# 

The interface can be recovered from errdisable state by reenabling the port using the errdisable recovery cause link-flap. This command is used to configure the recovery mechanism so that the interface can be brought out of the disabled state and allowed to try again. You can also set the time interval. Errdisable recovery is disabled by default in Cisco Switches; when enabled, the default time interval is 300 seconds.

Once you enable the errdisable state you can see the following log in the Cisco switch which is trying to recover the error disable interface (link-flap error)

13w0d: %PM-4-ERR_RECOVER: Attempting to recover from link-flap err-disable state on Fa0/28