Monday, December 16, 2013

Cisco: What Is The "Deferred Counter" In A Router Or Switch Interface?

This question came up as well around the topic of the 'late collision' pursuit.  Here is the 'deferred counter' definition:

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
  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.

1 comment:

  1. 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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