Solved: Re: Router Interface Duplex/Speed Settings

johnlloyd_13 · ‎10-28-2010

hi experts,

i would like to know which command output to refer when finding out duplex/speed settings on the router's interface. show interface displays full/100 while show run interface displays auto.

ROUTER#sh int f0/1
FastEthernet0/1 is up, line protocol is up
Hardware is Gt96k FE, address is 0017.95bb.44a3 (bia 0017.95bb.44a3)
Description: LAN
Internet address is 192.168.1.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 2/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 100Mb/s, 100BaseTX/FX -->
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:20, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 469000 bits/sec, 238 packets/sec
5 minute output rate 917000 bits/sec, 243 packets/sec
     2327169929 packets input, 1519671819 bytes
     Received 3 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog
     0 input packets with dribble condition detected
     2356621577 packets output, 3748937506 bytes, 0 underruns
     0 output errors, 0 collisions, 3 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out

ROUTERW#sh run int f0/1
Building configuration...

Current configuration : 145 bytes
!
interface FastEthernet0/1
description LAN
ip address 192.168.1.1 255.255.255.0
duplex auto -->
speed auto -->
no keepalive
end

Jon Marshall · ‎10-28-2010

John

If you have configured the interface to auto-negotiate then to see the actual speed/duplex the interface is running you must look at the output of the "sh interface " command. The reason being that if the interface is set to auto it could negotiate to different things eg. 10 full duplex/100 half duplex/100 full duplex etc.. You will only know what the interface is actually running at by looking at the output of "sh interface ..." because if you look at the "sh run" output all it will tell you is that the interface is configured to auto-negotiate.

However if you manually set the speed and duplex under the interface then you only need to look at the output of "sh run" because it will tell you what speed/duplex it is using, although if you are experiencing problems i would still check the output of "sh interface .."

Jon

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