A common question folks ask is "How do you check the bandwidth utilization on a router?"

It is a great question and the answer is not as easy as you would expect. There are tools that accomplish this (i.e. NetFlow and there is another mentioned at the end of this page). However, without those tools, there are two places to look and consider. The first is Interface usage and the second is CPU utilization. Let's look at these.

Interface Usage/Occupancy

The best command to begin is the "show interface" command. The problem is the output is large (see sample - I have not highlighted all the output). You are looking for the highlighted information. It is a 5 minute input rate, 5 minute output rate per interface. This is weighted (so be careful). Here is Cisco's explanation:

"Average number of bits and packets transmitted per second in the last 5 minutes. If the interface is not in promiscuous mode, it senses network traffic that it sends and receives (rather than all network traffic).

The 5-minute input and output rates should be used only as an approximation of traffic per second during a given 5-minute period. These rates are exponentially weighted averages with a time constant of 5 minutes. A period of four time constants must pass before the average will be within 2 percent of the instantaneous rate of a uniform stream of traffic over that period.

Note The 5-minute period referenced in this output is a load interval that is configurable under the interface. The default value is 5 minutes."


Here is an example output:

CSI-Router11#show interface
Serial0/0 is administratively down, line protocol is down
Hardware is CD2430 in sync mode
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input never, output never, 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
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 3 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=down DSR=down DTR=down RTS=down CTS=down
Serial0/1 is up, line protocol is up
Hardware is CD2430 in sync mode
Description: Interface to Router 12
Internet address is 192.168.100.58/30
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:00, output 00:00:05, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/2/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
966184 packets input, 79201411 bytes, 0 no buffer
Received 356525 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
963972 packets output, 79228151 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
4 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
Serial0/2 is up, line protocol is up
Hardware is CD2430 in sync mode
Description: Interface to Router 13
Internet address is 192.168.100.66/30
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:04, output 00:00:02, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/2/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
966235 packets input, 79190241 bytes, 0 no buffer
Received 356519 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
964793 packets output, 79418371 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
5 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
Serial0/3 is up, line protocol is up
Hardware is CD2430 in sync mode
Description: Interface to Router 2
Internet address is 192.168.100.42/30
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:03, output 00:00:03, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/2/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
612659 packets input, 53550688 bytes, 0 no buffer
Received 356467 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
1322149 packets output, 95117756 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
5 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
Serial0/4 is administratively down, line protocol is down
Hardware is CD2430 in sync mode
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input never, output never, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/0/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=down DSR=down DTR=down RTS=down CTS=down
Serial0/5 is administratively down, line protocol is down
Hardware is CD2430 in sync mode
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input never, output never, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/0/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=down DSR=down DTR=down RTS=down CTS=down
Serial0/6 is administratively down, line protocol is down
Hardware is CD2430 in sync mode
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input never, output never, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/0/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=down DSR=down DTR=down RTS=down CTS=down
Serial0/7 is administratively down, line protocol is down
Hardware is CD2430 in sync mode
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input never, output never, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/0/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=down DSR=down DTR=down RTS=down CTS=down
Ethernet3/0 is up, line protocol is up
Hardware is AmdP2, address is 00d0.58ec.74f1 (bia 00d0.58ec.74f1)
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 00:00:01, output 00:00:01, 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
1848245 packets input, 142097321 bytes, 0 no buffer
Received 1653877 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
576523 packets output, 53370905 bytes, 0 underruns
0 output errors, 5 collisions, 4 interface resets
0 babbles, 0 late collision, 18 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
Ethernet3/0.1 is up, line protocol is up
Hardware is AmdP2, address is 00d0.58ec.74f1 (bia 00d0.58ec.74f1)
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 1.
ARP type: ARPA, ARP Timeout 04:00:00
Last clearing of "show interface" counters never
Ethernet3/0.101 is up, line protocol is up
Hardware is AmdP2, address is 00d0.58ec.74f1 (bia 00d0.58ec.74f1)
Description: Interface to AS65200 Router 14
Internet address is 172.16.1.1/30
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 101.
ARP type: ARPA, ARP Timeout 04:00:00
Last clearing of "show interface" counters never
TokenRing3/0 is administratively down, line protocol is down
Hardware is IBM2692, address is 000b.1a37.2e4f (bia 000b.1a37.2e4f)
MTU 4464 bytes, BW 16000 Kbit, DLY 630 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation SNAP, loopback not set
Keepalive set (10 sec)
ARP type: SNAP, ARP Timeout 04:00:00
Ring speed: 16 Mbps
Duplex: half
Mode: Classic token ring station
Ethernet Transit OUI: 0x000000
Last input never, output never, 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
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 transitions
Loopback0 is up, line protocol is up
Hardware is Loopback
Internet address is 192.168.100.11/32
MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation LOOPBACK, loopback not set
Last input 4w6d, output never, 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: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
13 packets output, 988 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out

Now if you know the interface you just get that info which is easier to parse as shown:

CSI-Router11#show interface serial0/1
Serial0/1 is up, line protocol is up
Hardware is CD2430 in sync mode
Description: Interface to Router 12
Internet address is 192.168.100.58/30
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:05, output 00:00:04, 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: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/2/32 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
966424 packets input, 79220783 bytes, 0 no buffer
Received 356612 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
964211 packets output, 79247351 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
4 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up

If you want to change the 5 minute interval, you do the following using the load-interval command to change the time period (again, the default is 5 minutes) - let's change it to 30 seconds:

configure terminal
interface xxx
load-interval 30

Note this is done on each interface.

The "show interface accounting" command shows ratios, but it is hard to derive exact bandwidth utilization:

CSI-Router11#show interface accounting
Interface Serial0/0 is disabled

Serial0/1 Interface to Router 12
Protocol Pkts In Chars In Pkts Out Chars Out
Other 0 0 305644 7335456
IP 305609 26018196 303439 25713036
CDP 50945 18925793 50943 18937725
IPv6 304177 26937904 304144 27257892
Serial0/2 Interface to Router 13
Protocol Pkts In Chars In Pkts Out Chars Out
Other 0 0 305643 7335432
IP 305592 26016776 304131 25872292
CDP 50943 18925327 50943 18937641
IPv6 304247 26928436 304269 27288636
Serial0/3 Interface to Router 2
Protocol Pkts In Chars In Pkts Out Chars Out
Other 0 0 305634 7335216
IP 0 0 491819 33057584
CDP 50937 20298584 50942 18937305
IPv6 256239 25928020 474021 35806817
Interface Serial0/4 is disabled

Interface Serial0/5 is disabled

Interface Serial0/6 is disabled

Interface Serial0/7 is disabled

Ethernet3/0 
Protocol Pkts In Chars In Pkts Out Chars Out
Other 101868 4889664 305645 18338700
IP 98054 5883240 98054 6275456
DEC MOP 0 0 5095 392315
ARP 206 12360 208 13312
CDP 50935 19457170 50943 17536650
IPv6 113329 10111660 116691 10824965
Interface TokenRing3/0 is disabled

Loopback0 
Protocol Pkts In Chars In Pkts Out Chars Out
IPv6 13 988 13 988

Lastly, the show interface summary command provides an inetresting output:

CSI-Router11#show interface 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
------------------------------------------------------------------------
Serial0/0 0 0 0 0 0 0 0 0 0
* Serial0/1 0 0 0 0 16000 7 14000 7 0
* Serial0/2 0 0 0 0 0 0 0 0 0
* Serial0/3 0 0 0 0 0 0 0 0 0
Serial0/4 0 0 0 0 0 0 0 0 0
Serial0/5 0 0 0 0 0 0 0 0 0
Serial0/6 0 0 0 0 0 0 0 0 0
Serial0/7 0 0 0 0 0 0 0 0 0
* Ethernet3/0 0 0 0 0 0 0 0 0 0
* Ethernet3/0.1 - - - - - - - - -
* Ethernet3/0.101 - - - - - - - - -
TokenRing3/0 0 0 0 0 0 0 0 0 0
* Loopback0 0 0 0 0 0 0 0 0 0

Interface IHQ IQD OHQ OQD RXBS RXPS TXBS TXPS TRTL
------------------------------------------------------------------------
NOTE:No separate counters are maintained for subinterfaces
Hence Details of subinterface are not shown

CPU utilization

This one is easy - show processes - just the first line (I have omitted the complete output).

CSI-Router11#show processes
CPU utilization for five seconds: 2%/0%; one minute: 1%; five minutes: 1%
PID QTy PC Runtime (ms) Invoked uSecs Stacks TTY Process
1 Cwe 6050B420 0 2 0 5664/6000 0 Chunk Manager
2 Csp 604F39E8 644 611343 1 2524/3000 0 Load Meter
3 M* 0 600 243 246910204/12000 0 Exec
4 Mwe 6163F1F0 0 1 023372/24000 0 EDDRI_MAIN
5 Lst 60508338 4525184 363449 12450 5388/6000 0 Check heaps
6 Cwe 6050F0B0 0 2 0 5564/6000 0 Pool Manager
7 Mst 60416020 0 2 0 5492/6000 0 Timers
...


Alright, so without any tools, these two command sets are probably the the best way to get an idea of bandwidth utilization on a router. you should also check out this tool: http://www.ipbalance.com/traffic-analysis/traffic-monitoring/247-quick-realtime-bandwidth-monitoring-by-snmp-tool-stg.html

It is pretty good, and it is free, but requires some preparation and SNMP access.

We hope this helps.

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