[c-nsp] Deferred packets on 2950 10/full interface

[John Neiberger]

Just as a rule of thumb, if you use any of Cisco's newer switches,
including the 2950, it's best practice not to hard-set your speed and
duplex unless you know for certain that the device you're connecting
does not support autonegotiation. Here's the short explanation of why it
_might_ be failing in your situation:

When you hard-set these settings on the 2950, autonegotiation is
completely disabled. However, many devices still participate in
autonegotiation even when their settings have been set manually. They
would simply only offer their manually configured settings as being
available. If that type of device is manually configured for full duplex
but it does not detect an autonegotiating device on the other end, it
will assume that it is connected to a hub and will drop back to half
duplex regardless of the configured settings.

It's possible--and I see this a LOT--that the device being connected
still participates in autonegotiation despite being manually configured
for 10/Full. I know from experience (we have a lot of them) that the
2950 disables autonegotiation completely. Fixing duplex mismatches
caused by this problem used to be a daily occurrence for me. It's now
only a weekly occurrence. :)

If you want to do a quick test, remove your manually configured
settings and see what happens. If the other side is still participating
in autonegotiation, there's no reason not to let it work as intended. If
your errors clear up, you'll know what the problem was.

Regards,
John
--

>>> <jexum at harding.edu> 1/14/05 3:39:22 PM >>>
I have seen a 2950G-48 port connected to a Packeteer 4500, both set to
100 Full Duplex not work duplexity out correctly.  I have seen the same
happen between an Enterasys E-7 blade and a different 2950.

In both cases an update on the other device "fixed" the Cisco switch.

John Exum
Network Manager
Harding University

----- Original Message -----
From: Clinton Work <clinton at scripty.com>
Date: Friday, January 14, 2005 4:25 pm
Subject: [c-nsp] Deferred packets on 2950 10/full interface

> 
> I'm seeing 3716 deferred frames on a 10/full interface. I suspect 
> a 
> duplex mismatch even though the Telco assures me that their 
> interface is 
> 10/full as well. Anybody seen this problem on another 2950 switch?
> 
> 
> Router#show int fa0/1
> FastEthernet0/1 is up, line protocol is up (connected)
>   Hardware is Fast Ethernet, address is 000e.38a0.3901 (bia 
> 000e.38a0.3901)   Description:
>   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)
>   Full-duplex, 10Mb/s
>   input flow-control is off, output flow-control is off
>   ARP type: ARPA, ARP Timeout 04:00:00
>   Last input 00:00:00, output 00:00:05, output hang never
>   Last clearing of "show interface" counters 6w0d
>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output 
> drops: 0
>   Queueing strategy: fifo
>   Output queue :0/40 (size/max)
>   30 second input rate 0 bits/sec, 0 packets/sec
>   30 second ouxtput rate 0 bits/sec, 0 packets/sec
>      2979697 packets input, 477032533 bytes, 0 no buffer
>      Received 2612753 broadcasts, 241 runts, 0 giants, 0 throttles
>      316 input errors, 0 CRC, 75 frame, 0 overrun, 0 ignored
>      0 watchdog, 2612346 multicast, 0 pause input
>      0 input packets with dribble condition detected
>      1110744 packets output, 296966944 bytes, 0 underruns
>      0 output errors, 0 collisions, 0 interface resets
>      0 babbles, 0 late collision, 3716 deferred
>      0 lost carrier, 0 no carrier, 0 PAUSE output
>      0 output buffer failures, 0 output buffers swapped out
> 
> IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(13)EA1, 
> RELEASE 
> SOFTWARE (fc1)
> Copyright (c) 1986-2003 by cisco Systems, Inc.
> Compiled Tue 04-Mar-03 02:14 by yenanh
> Image text-base: 0x80010000, data-base: 0x805A8000
> Model number: WS-C2950-12
> 
> 
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