Basic port configuration¶
Speed and duplex¶
It can be useful to configure half-duplex if you’re connecting to some old tech, like a hub. For the user facing ports, you will probably prefer auto speed for these ports. However, autoconfiguration does not alway work within the infrastructure, and you may prefer to set link speed manually.
SW2(config)#int fa 1/0/30 SW2(config-if)#speed ? 10 Force 10 Mbps operation 100 Force 100 Mbps operation auto Enable AUTO speed configuration SW2(config-if)#speed auto
SW2(config-if)#duplex ? auto Enable AUTO duplex configuration full Force full duplex operation half Force half-duplex operation SW2(config-if)#duplex half
Another option worth knowing is MDIX. It’s the mechanism that allows the switch to know which twisted pair to use for transmission, and which for reception. It’s on auto by default, and can only be auto on my Catalyst 3750.
SW2(config-if)#mdix ? auto Enable automatic MDI crossover detection on this interface SW2(config-if)#mdix auto
Get info on a specific interface¶
SW2#show int fa 1/0/30 FastEthernet1/0/30 is up, line protocol is up (connected) Hardware is Fast Ethernet, address is 0015.2b2e.3c22 (bia 0015.2b2e.3c22) 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 00:00:01, 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 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 7041 packets input, 513625 bytes, 0 no buffer Received 5118 broadcasts (0 multicast) 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 watchdog, 5060 multicast, 0 pause input 0 input packets with dribble condition detected 2541 packets output, 256741 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 PAUSE output 0 output buffer failures, 0 output buffers swapped out
This command also works with other interfaces like VLANs etc.