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Telco Speed Duplex Problem with ASA


I am having issue with a Firewall attached to our Telco router.

I have been told by the Telco (and had confirmed) that their customer facing interface is force set to 100MB/FULL DUPLEX.

However no matter what I set on the ASA (Auto/Auto or 100/FULL) I still see 100MB/HALF DUPLEX on the show interface command on the ASA. I am also seeing some minor collisions.

Please can someone advise on exactly what the show interface command in this case means; in particular what the bracketed (Half-duplex) refers to???

For information purposes the connection remains active with either setting.

Interface GigabitEthernet0/0 "outside", is up, line protocol is up

Hardware is i82546GB rev03, BW 1000 Mbps, DLY 10 usec

Full-duplex(Half-duplex), 100 Mbps(100 Mbps)

MAC address xxxx.xxxx.xxxx, MTU 1500

IP address, subnet mask

954673 packets input, 1117595545 bytes, 0 no buffer

Received 20504 broadcasts, 0 runts, 0 giants

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

1 L2 decode drops

681592 packets output, 256981629 bytes, 0 underruns

0 output errors, 370 collisions, 13 interface resets

379 late collisions, 7333 deferred

0 input reset drops, 0 output reset drops

input queue (curr/max packets): hardware (0/14) software (0/0)

output queue (curr/max packets): hardware (0/15) software (0/0)


Re: Telco Speed Duplex Problem with ASA

In your case Full-duplex = configured duplex and Half-duplex=negotiated duplex. When auto-negotiation fails or is disabled, speed can be 'sensed' by the device but the devices fall back to half duplex as duplex is something that either has to be same on both ends or has to be negotiated.

It is apparent that your ISP has not properly configured his end. Double check that. Have a look at this:

(scroll down to the duplex mismatching section)