Cisco Catalyst 6000 Series Switches

Field Notice: Performance Issue with Intel Pro/1000T NICs connecting to CAT4K/6K

January 13, 2001

Products Affected


Top Assembly

Printed Circuit Assembly


HW Rev.

Part Number


Part Number




Ship Since May 2000




Ship Since May 2000



Problem Description

Customers may experience poor performance or see errors on the NICs when they connect the Intel Pro/1000 T Gigabit Copper NICs to Catalyst 4K/6K Copper Gigabit modules, WS- X4412-2GE-T or WS-X6316-GE-TX.


The interoperability issue arises from the implementation of Carrier Extension. Carrier Extension is detailed in sub section in the IEEE 802.3 specification. Carrier Extension can be used to pad the last byte of a packet, so the packet is aligned on an even numbered boundary.

All 1000 BASE-T interfaces are required to support carrier extension if it is present. Cisco shipped two copper modules, WS-X6316-GE-TX and WS-X4412-2GE-T since May 2000. Its 1000BASE-T interface on both modules have interoperability problem with Intel Pro/1000 T Server Adapter .When a Gigabit Copper NIC that does not correctly support carrier extension is connected to a single speed 1000 BaseT Catalyst switch, you may see performance issues.

Problem Symptoms

When an Intel Pro/1000 T NIC is connected to a Catalyst switch, customers may see poor network connections or excessive numbers of dropped packets .The interoperability issue arises when a module with TBI interface transmit an odd byte packet to a receiver with GMII interface.

This is because the Cisco WS-X6316-GE-TX and Cisco WS-X4412-2GE-T modules force even-length packets with Carrier Extension. They do this by adding one byte of padding to the end of odd length packets. This extra data in the packet causes the hardware CRC check to fail on the Intel Pro 1000 T NIC.

To verify this is the issue, ping an even sized packet and ping with an odd size packet:

Ping an even size packet
Ping (ip address) -l 72

Ping an odd size packet
Ping (ip address) -l 73 

Where the problem exists, the even size packet ping succeeds and the odd size packet ping fails.

The Catalyst 1000 Base T modules, WS-X6316-GE-TX and WS-X4412-2GE-T, while generating even length packets, can receive odd and even length packets without error.


Intel has implemented a workaround in their latest driver. With this workaround, odd-length packets are correctly received by the host, although they will still be counted incorrectly as CRC errors by the NIC. Intel's modified driver strips the extra byte from padded packets, so the host receives the payload of padded packets intact.

For more information, check workaround on Intel software driver patch

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

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