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The %PM_SCP-SP-3-LCP_FW_ABLC: Late collision message from module error message appears in Catalyst 6500 Switches that runs Cisco IOS software


Core issue

A message similar to this example appears in the logs:

Sep 20 09:43:13: %PM_SCP-SP-3-LCP_FW_ABLC: Late collision message from module 2, port:047


Feb 21 06:38:52 PST: %PM_SCP-SP-4-LCP_FW_ABLC: Late collision message from module 7,port:037

This means that the line card firmware detected abnormal collisions in port traffic. Usually, this is a temporary situation.

Late collision means the number of times that a collision is detected on a particular interface late in the transmission process.

For a 10 Mbit/s port, this is later than 512 bit-times into the transmission of a packet. 512 bit-times corresponds to 51.2 microseconds on a 10 Mbit/s system. This error can indicate a duplex mismatch, among other things. For the duplex mismatch scenario, the late collision is seen on the half-duplex side. As the half-duplex side transmits, the full-duplex side does not wait its turn and transmits simultaneously. This causes a late collision. Late collisions can also indicate an Ethernet cable or segment that is too long. Collisions should not be seen on interfaces configured as full-duplex.

The error message is caused by excessive Abort Late Collision counts on the specified port or the line card firmware has detected abnormal collisions in port traffic. This is caused by a duplex mismatch between the port and the device plugged into that port.

A late collision occurs when two devices transmit at the same time and neither side of the connection detects a collision. The reason for this occurrence is because the time to propagate the signal from one end of the network to another is longer than the time to put the entire packet on the network. The two devices that cause the late collision never see that the other sends until after it puts the entire packet on the network. Late collisions are not detected by the transmitter until after the first 64-byte slot time. This is because they are only detected during transmissions of packets longer than 64 bytes. Its detection is exactly the same as for a normal collision, it just happens later when compared to a normal collision.


In order to resolve this issue, check to see if both sides of the link or port mentioned in the error message are set for the same speed/duplex.

For correct operation, both sides of a link need to be auto-negotiated or both sides need to be hard set for speed duplex. If you auto-negotiate one side of a link and hard set the speed/duplex on the other side, it does not work as the side that does auto negotiating possibly locks itself at wrong duplex setting.

For further assistance and support, use the TAC Service Request Tool in order to open a case with Cisco Technical Support.

Community Member

Thank you, It's help my case.