Fix or Auto Duplex and Speed Settings
Short summary
| 1) | Fixed
settings are the right thing for connections between routers, switches,
firewalls, VPN concentrators, ... and servers. See e.g. http://www.cisco.com/warp/public/784/packet/apr02/techtips.html You can also take advantage of fixed configuration for printers. |
| 2) | If
auto-negotiation is used, it has to be used on both sides (switch and
client) otherwise its likely to result in misconfiguration of duplex. That's a good choice clients, switches and VoIP phones. |
| 3) | Fixed
settings for clients are a disadvantage because clients and especially
notebook users tend to move often and settings at home or in a hotel might
be different. --> Manual configuration change needs to be done by the user when roaming. --> Fixed settings on client based equipment can be a new source of trouble e.g. if not kept consistent everywhere. |
| 4) | There
are indicators to find out if there is a duplex mismatch or not:
Collisions and Errors See also my short technical guide further down to find out how to gather this information. |
An extensive description of how and
why things work as they do can be found here:
http://www.cites.uiuc.edu/network/autosense.html
Short tech guide to troubleshoot duplex
mismatch
PC statistics:
Check if errors are 0 or a very small number:
C:\>netstat -e
Interface Statistics
Received
Sent
Bytes
8453708 1321227
Unicast packets
17946 15388
Non-unicast packets
7490
53
Discards
0
0
Errors
0
0
Unknown protocols
650
C:\>
Phones configuration - on the phone:
Settings, 3 Network Configuration:
40
SW Port Configuration
41
PC Port Configuration
Phones configuration - phone web page (e.g.
my phone):
http://10.248.22.200/NetworkConfiguration
Phones statistic - phone web page (e.g. my
phone):
http://10.248.22.200/EthernetInformation
- Check if Collisions and Errors are 0 or a very small number
http://10.248.22.200/PortInformation?1
- Port to switch - Check
if Collisions are 0 or a very small number
http://10.248.22.200/PortInformation?2
- Port to PC - Check if
Collisions are 0 or a very small number
Switch port configuration - on Cisco 3524 or
3550:
Search for
entries like "speed 100" or "duplex half".
If they're absent, "speed auto"
and "duplex auto" are configured.
switch-1#sh run int fas 0/4
Building configuration...
Current configuration:
!
interface FastEthernet0/4
switchport trunk encapsulation dot1q
switchport mode trunk
switchport voice vlan 999
spanning-tree portfast
end
switch-1#
Switch port active settings and statistic -
on Cisco c3524 or c3550:
switch-1#sh int fas 0/4
FastEthernet0/4 is up, line protocol is up
Hardware is Fast Ethernet, address is
0009.e875.b944 (bia 0009.e875.b944)
MTU 1500 bytes, BW 100000 Kbit, DLY 100
usec,
reliability 255/255,
txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Auto-duplex (Full), Auto Speed (100),
100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:14, output 00:00:01,
output hang never
Last clearing of "show
interface" counters never
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue
0/75, 0 drops
5 minute input rate 71000 bits/sec, 50
packets/sec
5 minute output rate 52000 bits/sec, 32
packets/sec
32935052 packets
input, 764585029 bytes
Received 206595
broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors,
0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 185821
multicast
0 input packets with
dribble condition detected
55474898 packets
output, 3660581318 bytes, 0 underruns
0 output errors, 0
collisions, 1 interface resets
0 babbles, 0 late
collision, 0 deferred
0 lost carrier, 0 no
carrier
0 output buffer
failures, 0 output buffers swapped out
switch-1#
Created and copyright by Raphael Müller, Last Update: 22. January 2004