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Cannot autonegotiate port speed and duplex due to port configuration or NIC driver capability


Core issue

Network Interface Card (NIC) driver or misconfiguration of duplex/speed settings cause autonegotiation to fail.


Ensure that autonegotiation is configured on both ends of the link. On the switch, issue the show port command to display the current settings.

Do not configure these settings manually on one end of the link and for autonegotiation on the other end.

If autonegotiation fails when connecting a client NIC to the switch, check the NIC and drivers to ensure that autonegotiation is supported.

For more information, refer to Understanding Data Link Errors section of Troubleshooting Cisco Catalyst Switches to NIC Compatibility Issues.

If autonegotiation is supported and properly configured but a connection still cannot be established, turn off autonegotiation by setting the speed and duplex manually. Issue the set port speed and set port duplex commands. Be sure that both ends of the link are configured with the same speed and duplex settings.

Symptoms of a failed link include Frame Check Sequence (FCS) and alignment errors. The FCS error count is the number of frames that were transmitted/received with a bad checksum (Cyclic Redundancy Check (CRC) value) in the Ethernet frame. These frames are dropped and not propagated onto other ports. Alignment errors are a count of the number of frames received that do not end with an even number of octets and have a bad CRC.

Issue the show port command to see if these counters are incrementing on a CatOS switch.

Issue the show interface command to check for CRC errors on a Cisco IOS -based switch.

This is an example of the counters from the show port command from a CatOS switch:

Console> (enable) sh port 1/1

Port  Align-Err  FCS-Err    Xmit-Err   Rcv-Err    UnderSize
----- ---------- ---------- ---------- ---------- ---------
1/1           0          0          0          0         0

Console> (enable)

Below is an example of the show interface command from an IOS-based switch.

Switch#show int fa 0/5

FastEthernet0/5 is down, line protocol is down

Hardware is Fast Ethernet, address is 0001.427b.3a45 (bia


MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Auto-duplex , Auto Speed , 100BaseTX/FX

ARP type: ARPA, ARP Timeout 04:00:00

Last input never, output 2d06h, output hang never

Last clearing of "show interface" counters never

Queueing strategy: fifo

Output queue 0/40, 0 drops; input queue 0/75, 0 drops

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

1 packets input, 64 bytes

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun,0 ignored

0 watchdog, 0 multicast

0 input packets with dribble condition detected

3 packets output, 806 bytes, 0 underruns

0 output errors, 0 collisions, 1 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier

0 output buffer failures, 0 output buffers swapped out


For more information regarding autonegotiation, refer to Configuring and Troubleshooting Ethernet 10/100/1000Mb Half/Full Duplex Auto-Negotiation.