In a recent article, I listed five Cisco
IOS Interface Configuration Mode commands I thought everyone should know. As
usual, I asked readers to chime in with their suggestions in the article’s
discussion.
TechRepublic member Pwright
commented on the importance
of the show interfaces command
and recommended that I write an article expounding on this command. Pwright made a good point: If you don’t
know what’s really going on with the interfaces, you probably don’t really know
which changes you need to make. So, let’s take a closer look at the show interfaces command.
The purpose of the show
interfaces command is rather self-explanatory—it displays the interfaces
and their status. Here’s the information you can get about an interface from this
command:
- Interface
type - Status
- Speed
and duplex - Encapsulation
- Errors
on the interface - The last
time the interface bounced - The last
time the error counters reset - Utilization
- IP
address, subnet mask, and MAC address
In my opinion, here are the five most important uses for the
show interfaces command:
- Determine
if the interface is up and if the protocol is up. - Ascertain
if the interface has errors on it, especially CRC errors. - Find
out the speed and duplex of the interface (if it’s Ethernet). - Learn
the current utilization and utilization over the last five minutes. - Determine
the last time an interface bounced.
Listing A offers
sample output of the show interfaces command, displaying four different
types of interfaces: Gigabit Ethernet, Loopback, Tunnel, and Serial. Notice how
each type of interface has different types of output.
From this output, you can see that the show interfaces command
generates a lot of valuable information. However, when you have 25 interfaces
or more on a router, the output begins to get cumbersome. Let’s look at how you
can limit this output to get the information you need the most.
Know your options
The show interfaces command boasts a number of options that
allow you to limit the output information. You can specify the type of
interface as well as the interface number:
show interfaces {type of interface} {interface number}
Using these options, you can view output for a single
interface. Here’s an example:
Router# show interfaces ethernet 0/0 Ethernet0/0 is administratively down, line protocol is down Hardware is AmdP2, address is 0003.e39b.9220 (bia 0003.e39b.9220) Internet address is 1.1.1.1/8 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) ARP type: ARPA, ARP Timeout 04:00:00 Last input 4d06h, output never, 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 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 19 packets input, 2330 bytes, 0 no buffer Received 19 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 0 packets output, 0 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 output buffer failures, 0 output buffers swapped out Router#
You can also view of a summary of the output from the show interfaces command. Using this
option, you can get a summary of all interfaces and statistics about each one.
For example, say you’re looking for an interface that’s
exceeding a 512-Kbps receive rate or perhaps you want to find any interfaces
that are dropping packets from their input queue. Either way, this option can
help you find that information much quicker. Here’s an example:
Router# show interfaces summary *: interface is up IHQ: pkts in input hold queue IQD: pkts dropped from input queue OHQ: pkts in output hold queue OQD: pkts dropped from output queue RXBS: rx rate (bits/sec) RXPS: rx rate (pkts/sec) TXBS: tx rate (bits/sec) TXPS: tx rate (pkts/sec) TRTL: throttle count Interface IHQ IQD OHQ OQD RXBS RXPS TXBS TXPS TRTL ---------------------------------------------------------------------- Ethernet0/0 0 0 0 0 0 0 0 0 0 Serial0/0 0 0 0 0 0 0 0 0 0 Serial0/1 0 0 0 0 0 0 0 0 0 Router#
You can also use this command with the pipe command [|] and the
begin, include, or exclude
options. Here’s an example of using include:
Router# show interfaces | inc CRC 29 input errors, 29 CRC, 0 frame, 0 overrun, 0 ignored, 53 abort 1375 input errors, 5 CRC, 30 frame, 0 overrun, 0 ignored, 22 abort 24 input errors, 142 CRC, 19 frame, 9 overrun, 5 ignored, 64 abort 140 input errors, 14 CRC, 47 frame, 0 overrun, 0 ignored, 30 abort 114 input errors, 9 CRC, 29 frame, 0 overrun, 0 ignored, 18 abort
You can use begin
to start the output on a line that contains a specific text string. This way,
you can skip to a specific point in the output rather than looking through all
of it. Here’s an example:
router# show interfaces | beg Serial Serial0/2 is up, line protocol is up Hardware is GT96K with 56k 4-wire CSU/DSU MTU 1500 bytes, BW 56 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation FRAME-RELAY IETF, loopback not set Keepalive set (10 sec) LMI enq sent 2586870, LMI stat recvd 2586785, LMI upd recvd 0, DTE LMI up LMI enq recvd 24, LMI stat sent 0, LMI upd sent 0 LMI DLCI 0 LMI type is ANSI Annex D frame relay DTE Broadcast queue 0/64, broadcasts sent/dropped 0/0, interface broadcasts 0 Last input 00:00:05, output 00:00:05, output hang never Last clearing of "show interface" counters 42w5d Input queue: 0/75/0/13 (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 9574781 packets input, 398755727 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 2761 input errors, 2761 CRC, 1120 frame, 624 overrun, 0 ignored, 2250 abort 9184611 packets output, 289103201 bytes, 0 underruns 0 output errors, 0 collisions, 195 interface resets 0 output buffer failures, 0 output buffers swapped out 668 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up
For more information on the show interfaces command, check
out Cisco’s documentation. Then, share your experiences with this
command—as well as your ideas for future articles—in this article’s discussion.
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David Davis has worked
in the IT industry for 12 years and holds several certifications, including
CCIE, MCSE+I, CISSP, CCNA, CCDA, and CCNP. He currently manages a group of
systems/network administrators for a privately owned retail company and
performs networking/systems consulting on a part-time basis.
