What is KEEPALIVE PACKET on 2950 Ethernet interface?

[pololo]

Dear All,

A C2950 connected to 3Com 3500 with FA0/1 for a year. Recently, the 2950 (FA0/1) was errdisabled by loopback.

LOG SHOW:

%ETHCNTR-3-LOOP_BACK_DETECTED: KEEPALIVE PACKET LOOP_BACK ON FASTETHERNET 0/1.

MY Question is

1) What is the cause? I have changed the inter-connected cable. It still remains.

2) What is Keepalive packet?

3) What is the meaning of Keepalive set in FA0/1

show interface FA0/1

Keepalive set (10 sec)

Yours

[allan.thomas]

Keepalives simply verify the integrity of the link. In this particualar case the FastEthernet interface is configured with the default 10 seconds.

Essentially this value means the frequency of the interval between successive keepalive messages, so the router will send a keepalive every 10 seconds in this case. In the event that the router does not receive 5 consecutive replies from the peer the interface will be taken down.

The error message suggests that a loopback was detected on port FA 0/1 and the port was forced down (errdisabled).

When you changed the cable did you run a no-shut on the interface to clear the errdisable state.