Understanding traffic volumes in 'Show Interfaces'

[marcjone]

Hi all

I would like to know more about how to determine the amount of traffic on an interface

For example, we are seeing CRC errors on one of our Serial interfaces and there is a document which states that "Any input error value for cyclic redundancy check (CRC) errors, framing errors, or aborts above 1 percent of the total interface traffic suggests some kind of link problem"

Should I total the number of input plus the number of output packets, or should I total the number of Bytes in and out of the interface ?

Also, it you have a 10MB interface for example, how much 'traffic' might this be able to handle ? And are there different rules for ethernet and serial interfaces ?

If anyone has an explanation or a document which explains more on this then that would be great !

Many thanks in advance - Marcus

[smif101]

Well the first thing I would do is do a clear counters to get everything set back to zero. To determine the bandwidth that is utilized on a serial interface enter the bandwidth command with the correct speed of the physical interface, it defaults to 1.544Mbs. From there when you do a show interface you will see the load percentage which is in the format like 10/255. Use that to get the percentage of bandwidth that is being consumed. To check the serial link for errors you can do loops and such with your carrier to isolate where the problem is by seeing the incrementing errors.

Jason Smith

www.smif101.com

[marcjone]

Many thanks for your reply

So, if I have a 'show int' like the following on a 10 meg ethernet interface, how do I determine the amount of traffic on the interface - is it [2295197 packets input + 3594664 packets output = 5889861] which is roughly 58% utilization ? I'm not sure if I am understanding this correctly or whether I am missing something ...

Router# show interfaces ethernet 0

Ethernet 0 is up, line protocol is up

Hardware is MCI Ethernet, address is aa00.0400.0134 (via 0000.0c00.4369)

Internet address is 131.108.1.1, subnet mask is 255.255.255.0

MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255

Encapsulation ARPA, loopback not set, keepalive set (10 sec)

ARP type: ARPA, PROBE, ARP Timeout 4:00:00

Last input 0:00:00, output 0:00:00, output hang never

Output queue 0/40, 0 drops; input queue 0/75, 2 drops

Five minute input rate 61000 bits/sec, 4 packets/sec

Five minute output rate 1000 bits/sec, 2 packets/sec

2295197 packets input, 305539992 bytes, 0 no buffer

Received 1925500 broadcasts, 0 runts, 0 giants

3 input errors, 3 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

0 input packets with dribble condition detected

3594664 packets output, 436549843 bytes, 0 underruns

8 output errors, 1790 collisions, 10 interface resets, 0 restarts

[smif101]

Ok where the MTU starts on that line and to the right you see the BW, rely and load statements. The bandwidth that you configure here lets the router know how to determine the load of the interface by how many bytes it is sending out its interfaces. For this particular interface the load is 1/255 which is .003%. So if the load was 128/255 it would be at 50% utilization. You don't need to worry about the bytes output and input. The load is the output rate so if you wanted to know the load for the recieve side you would look at the other ends serial interface. Rely is the reliablity of the interface, is this is other than 255/255 than you have a physical line problem.

[marcjone]

Thanks for your answers Jason - I appreciate it :)