[c-nsp] Ethernet Interfaces Speed and Duplex - Force or Auto

[Matlock, Kenneth L]

For us here, with 28,000+ Ethernet ports.

By default all our ports are set to auto. If the device on the other end can't support autonegotiation, only than do we hard-set ports.

Keep in mind on a lot of gear (Cisco included) that at 10/100 speeds, half-duplex is the default for duplex negotiation failure. This means if you hard-set one end to 100/Full and the other is auto, 99% of the time the auto side will come up 100/Half.

Rule of thumb for us is, both sides are auto, or both sides are hard-set. 

1gb speeds 'Full' is the default, but we still leave those ports at auto, and let the FLP's handle the negotiation.

Ken Matlock
Network Analyst
Exempla Healthcare
(303) 467-4671
matlockk at exempla.org


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jeff Wojciechowski
Sent: Thursday, May 20, 2010 1:19 PM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Ethernet Interfaces Speed and Duplex - Force or Auto

All:

Curious what other network admins are doing out there for Ethernet interfaces as far as speed and duplex settings - weather to specify or to leave them auto negotiate.

The reason I am asking is we just installed some equipment in a new data center we are in the process of bringing online for redundancy and the switch ports on the network switch at the new location are set to 100/full while the switch this equipment was built and tested on in our main facility was set to auto/auto.

Since equipment was moved to the new location I have been taking CRC errors on almost all active network ports that this equipment is plugged into yet the 3 months or so this system was in the other location with speed auto/duplex auto, we had none. I tried swapping out the network switch but I am still taking errors at about the same rate.

Show int of port with most errors (WS-C3560-24TS)

FastEthernet0/3 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 001c.0f21.d085 (bia 001c.0f21.d085)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 10/100BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:01, output hang never
  Last clearing of "show interface" counters 1d18h
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 2000 bits/sec, 3 packets/sec
  5 minute output rate 3000 bits/sec, 4 packets/sec
     533310 packets input, 64455460 bytes, 0 no buffer
     Received 5227 broadcasts (0 multicasts)
     0 runts, 0 giants, 0 throttles
     150 input errors, 69 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     556098 packets output, 59830579 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

During non-production hours, I will be setting those ports to auto/auto to see if the errors go away - but still curious what others are doing - and does it depend on what sort of device is using a port such as a server, router, another switch, pc, etc?

Thanks again,

Jeff Wojciechowski
LAN, WAN and Telephony Administrator
Midland Paper Company
101 E Palatine Rd
Wheeling, IL 60090
* tel: 847.777.2829
Ê fax: 847.403.6829
e-mail: jeff.wojciechowski at midlandpaper.com<mailto:jeff.wojciechowski at midlandpaper.com>
http://www.midlandpaper.com

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