err-disable in ethernet

Unanswered Question
Jul 29th, 2009


we are having cisco 2960 switch in our network and we are connected 7902 IP Phone and phones are working but when phone power on and off then that port is down and shown that err-disable, we are also do duplex setting on that port stil we are having same problem so how we can resolve this issues ???

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Lucien Avramov Wed, 07/29/2009 - 21:16

If you have enabled errdisable recovery, you can determine the reason for the errdisable status if you issue the show errdisable recovery command. Here is an example:

cat6knative#show errdisable recovery

ErrDisable Reason Timer Status

----------------- --------------

udld Enabled

bpduguard Enabled

security-violatio Enabled

channel-misconfig Enabled

pagp-flap Enabled

dtp-flap Enabled

link-flap Enabled

l2ptguard Enabled

psecure-violation Enabled

gbic-invalid Enabled

dhcp-rate-limit Enabled

mac-limit Enabled

unicast-flood Enabled

arp-inspection Enabled

Timer interval: 300 seconds

Interfaces that will be enabled at the next timeout:

Interface Errdisable reason Time left(sec)

--------- --------------------- --------------

Fa2/4 bpduguard 273

One you find the reason, you will be able to fix it.

Jayesh Prajapati Wed, 07/29/2009 - 22:35


I am not enable errdisable recovery command still it's happen if i am enable then also same .?????

Jayesh Prajapati Thu, 07/30/2009 - 00:03


I cheked "sh int status err-disabled "

and shown that reason "loopback" on interface but the thing is that port coonected to cisco 7902 IP Phone .

davy.timmermans Thu, 07/30/2009 - 00:08

Loopback error

A loopback error occurs when the keepalive packet is looped back to the port that sent the keepalive. The switch sends keepalives out all the interfaces by default. A device can loop the packets back to the source interface, which usually occurs because there is a logical loop in the network that the spanning tree has not blocked. The source interface receives the keepalive packet that it sent out, and the switch disables the interface (errdisable). This message occurs because the keepalive packet is looped back to the port that sent the keepalive:

Is the phone directly connected to the switch?

can you post STP related config + interface config

Jayesh Prajapati Thu, 07/30/2009 - 00:13


Yes IP phone directly connected to switch and particular that port we are facing problem.? can you advice me which type of configuration i have to do ?

davy.timmermans Thu, 07/30/2009 - 00:19

for access port

if a pc is connected to the phone and in a different vlan

switchport mode access

spanning-tree portfast

spanning-tree bpdugard enable

switchport access vlan x

switchport voice vlan y

switchport nonegotiate

Jayesh Prajapati Thu, 07/30/2009 - 00:23


Thank you for this but problem is that we have connected only IPPhone there is no pc ot like that ...only one IPPhone 7902 connected.


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