The Deferred Counter
Here is an example of output from the show interface command:
router#show interface ethernet 0 Ethernet0 is up, line protocol is up Hardware is Lance, address is 0010.7b36.1be8 (bia 0010.7b36.1be8) Internet address is 10.200.40.74/22 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:00, output 00:00:06, output hang never Last clearing of "show interface" counters never Input queue: 1/75/1/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: random early detection(RED) Output queue :0/40 (size/max) 5 minute input rate 1000 bits/sec, 2 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 2058015 packets input, 233768993 bytes, 1 no buffer Received 1880947 broadcasts, 0 runts, 0 giants, 1 throttles 3 input errors, 0 CRC, 0 frame, 0 overrun, 3 ignored 0 input packets with dribble condition detected 298036 packets output, 32280269 bytes, 0 underruns 0 output errors, 10 collisions, 0 interface resets 0 babbles, 0 late collision, 143 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
The deferred counter counts the number of times the interface has tried to send a frame, but found the carrier busy at the first attempt (Carrier Sense). This does not constitute a problem, and is part of normal Ethernet operation.
As long as you're seeing the deferred packets on half-duplex links, incrementing those counters is appropriate. There is definitely a problem if they happen on full-duplex links. Since you're using one of the old Lance ethernet PHYs, I'm assuming that your link is half-duplex in this case.
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