[c-nsp] understanding "reliability", "txload" and "rxload" parameters in output of "show int"

[Martin T]

As I understand, "txload" should indicate the load of the outgoing
traffic and "rxload" should indicate the load of incoming traffic.
1/255 should mean that there is no traffic on the interface and
255/255 should mean, that interface is completely saturated either in
Tx or Rx direction. "reliability", "txload" and "rxload" should be,
according to documentation, 5min average values.

Take a look at following three examples:


C4506#show interfaces Gi2/6 | i load|bits
     reliability 255/255, txload 60/255, rxload 67/255
  5 minute input rate 266423000 bits/sec, 59865 packets/sec
  5 minute output rate 235768000 bits/sec, 49981 packets/sec
C4506#show interfaces Fa6/31 | i load|bits
     reliability 255/255, txload 4/255, rxload 7/255
  5 minute input rate 309000 bits/sec, 119 packets/sec
  5 minute output rate 178000 bits/sec, 152 packets/sec
C4506#

2801#show interfaces Fa0/0 | i load|bits
     reliability 255/255, txload 7/255, rxload 28/255
  5 minute input rate 667000 bits/sec, 97 packets/sec
  5 minute output rate 176000 bits/sec, 77 packets/sec
2801#


For example in case "txload 60/255, rxload 67/255" it would mean that
in outgoing direction interface load is (60*100)/255=23.5% and in
incoming direction it's (67*100)/255=26.3% which are the correct
values if I check the "5 minute input/output rate". However, in case
of "Fa6/31"(duplex half, speed 10), in outgoing direction the load is
(4*100)/255=1.57% and in incoming direction it's (7*100)/255=2.75%
which are not exactly 0.309Mbps and 0.178Mbps on 10Mbps interface.
This is caused by rounding, right?

In case of "Fa0/0"(duplex full, speed 100), in outgoing direction the
load is (7*100)/255=2.75%(2.8Mbps) and in incoming direction it's
(28*100)/255=11.0%(11Mbps) which are rather far from 0.667Mbps and
0.176Mbps on 100Mbps interface. What causes this? Or does IOS
calculate the average of "5 minute input/output rate" and 5min
"txload/rxload" at different times? In other words "5 minute
input/output rate" and "txload/rxload" are not in sync?


C4506#show interfaces GigabitEthernet5/27 | i load|error
     reliability 254/255, txload 2/255, rxload 55/255
     3066206876 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 output errors, 0 collisions, 0 interface resets
C4506#

Interface Gi5/27 has average 200 errors per minute(average traffic is
Tx 180Mbps and Rx 8Mbps)- is this "reliability" also calculated like
"txload" and "rxload"? I mean in order to have "reliability" value
128, one should have half of the packets on the interface counted
counted as errors? If yes, then I would say everything <255 is a
serious problem.


Please correct me if I got something wrong :)


regards,
martin