txload and rxload relationship to input rate/output rate

[Jason Jackal]

Folks:

I have been reviewing the txload and rxload values in relationship to the input/output rate; however, I do not fully understand the difference between the four values. What is each value telling me?

From what I understand – txload and rxload take in account the interface bandwidth, but is the bandwidth value configured with the interface ‘bandwidth’ command?

If I want to know the average load on the interface – would I look under the following ‘sh int’ command output?

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 1000 bits/sec, 1 packets/sec

     454 packets input, 89091 bytes, 0 no buffer

This topic might have already been discussed in great detail; however, I am just having a hard time understanding without the social interaction.

Thank you.

[Ganesh Hariharan]

Jason Jackal wrote:
Folks:
I have been reviewing the txload and rxload values in relationship to the input/output rate; however, I do not fully understand the difference between the four values. What is each value telling me?
From what I understand – txload and rxload take in account the interface bandwidth, but is the bandwidth value configured with the interface ‘bandwidth’ command?
If I want to know the average load on the interface – would I look under the following ‘sh int’ command output?
5 minute input rate 0 bits/sec, 0 packets/sec
 5 minute output rate 1000 bits/sec, 1 packets/sec
     454 packets input, 89091 bytes, 0 no buffer
This topic might have already been discussed in great detail; however, I am just having a hard time understanding without the social interaction.
Thank you.

Hello ,

Rx load is nothing but the amount of traffic you are receiving on that particular wan interface. Rxload 80/255 means you are getting almost all 2.4Mbps from outside.Txload means the amount of traffice which is going out from your network.  Rxload inturn depends on Txload load.

255/255 is 100% utilization of a link, but most of the time even if you have full utilization you'll see a reported value of something like 248+/255.The reliability of an interface is always reported as a fraction of 255 (255/255 is 100% reliability), calculated as an exponential average over 5 minutes.  So you want to see the reliability at 255/255.  If this drops below this value, then you have problems on the link.  Typically, any layer 1 or layer 2 issues will bring this number down say 228/255.

The load on an interface is also a fraction of 255 (255/255 is completely saturated), and is also calculated as an exponential average over 5 minutes.   You do NOT want to see the TX load or RX load at 255/255 or 100%, as this indicates a saturated link.  The configured bandwidth on the interface and the actual bandwidth utilized affect this number.  For example, you have a 100Mbps link and it is 50% utilized, you should see something like 128/255.

Hope to Help !!

Ganesh

[Jason Jackal]

ganeshh.iyer

How did you come up with "2.4 Mbps"?  Since you said 128/255 is roughly 50%, then the math would be

80/255 = 0.31 or 31%.

So if we follow your example.

7.74*0.31=2.4 Mbps

Does that mean you have roughly a 7.74 Mbps outside link?

Sorry just really confused.

If the txload and rxload are based off the bandwidth of the interface, then the default values for Gig and Fast interfaces should represented by the x/255 as a percentage of the interface?

[Joseph W. Doherty]

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Posting

ganeshh.iyer wrote:
You do NOT want to see the TX load or RX load at 255/255 or 100%, as this indicates a saturated link.  

As a side comment, a link with 100% utilization isn't always a bad thing.

[Vincenzo Errante]

hi,

this is just an copy and paste

txload/rxload=Load on the interface as a fraction of 255 (255/255 is completely saturated), calculated as an exponential average over 5 minutes.

255=100%, 128=50%, 64=25%, 32=12%, 16=6%, 8=3%, 4=1.5%

regards

[Jason Jackal]

Thank you for the values - as my previous post shows, I am super confused on these items.

[Peter Paluch]

Hi Jason,

To add to other friends' answers here:

txload = output rate / configured bandwidth * 255

rxload = input rate / configured bandwidth * 255

In other words, txload and rxload express the fraction of used bandwidth (as configured by the bandwidth command on the interface) by the traffic flowing in either direction, on a scale of 1-255. I am not quite sure why the scale of 1-255 was chosen but it seems to nicely fit into the formula used by IGRP/EIGRP, and that is probably the reason for having these obscure counters at all.

Best regards,

Peter

[Jason Jackal]

Hi Peter Paluch:

Thank you for the math. I posted earlier, but was having  a hard time calculating the math.

Is it safe to assume that txload and rxload are calculated based off the input/output rate of the interface? During troubleshooting – what do I look at to see if the interface is getting over-utilized?

[Peter Paluch]

Hi Jason,

Is it safe to assume that txload and rxload are calculated based off the input/output rate of the interface? 

Yes. There is nothing else you can base the calculation on, anyway - only the amount of data currently flowing through the interface. The input/output rates are absolute values. The rxload/txload are relative values.

During troubleshooting – what do I look at to see if the interface is getting over-utilized? 

Probably at the txload/rxload, although you have to keep in mind that this scale is not from 0% to 100% but rather from 1-255. A nice recalc table for most common values was given by Vincenzo.

Best regards,

Peter

[Jason Jackal]

Peter,

I understand and thank you.

So is the txload/rxload values related to the time pull on the input/output statistics? While the input/output values are averages for the value of time configured?

[Jason Jackal]

Peter,

txload = output rate / configured bandwidth * 255
rxload = input rate / configured bandwidth * 255

What do I convert the values to? Bandwidth is configuered in kilobits and 'output/input' are shown in bits/sec. Do I convert both values to the lowest units?

Thanks

[Peter Paluch]

Hi Jason,

What do I convert the values to? Bandwidth is configuered in kilobits  and 'output/input' are shown in bits/sec. Do I convert both values to  the lowest units?

Convert it to kilobits per second. As this is basically a fraction (a ratio), you may convert it to whatever identical units, as in division, the multipliers (kilo-, mega-, ...) will eliminate themselves. However, using the kbps is the most straightforward as the configured bandwidth is already in kilobits per second and does not need any recalculation.

Best regards,

Peter

[Leo Laohoo]

Can I add something?

This is in regards to the value of X/255 (Txload & Rxload) and the value of 255/255 (Reliability).

The value of "255" means that your link is WORKING 100%.

If you punch in the command "sh interface " and your Txload or Rxload is showing like X/254 (or lower) then you have a potential cable problem.

Same goes with the Reliability value.  The value of 255/255 means it's working great.  Two-thumbs-up.  However, if the either value dips to 254 and below then you have a cable issue. 

[Peter Paluch]

Leo,

Good one! Thanks! And you are always welcome to add anything you see useful.

Best regards,

Peter

[Leo Laohoo]

Thanks Peter.