The overall reliability or load of an interface at a given point in time can be measured by the txload/rxload a fractional ( 255/255 = 100% ) calculation over a default average of 5 minutes. This 5 minute time interval is the default on most if not all Cisco devices, however it can be changed or tuned if necessary. We always want to see the overall reliability at 255/255 which basically means all is good. The thing to remember with regards to txload/rxload reliability is that they both make up the same 255. For example you wouldn’t see the txload at lets say 200/255 and the rxload 60/255 that would equal an overall reliability of 260.
Lets take for example the following GigabitEthernet interface on Cisco 2901 router.
Router#show interface GigabitEhternet0/0
GigabitEthernet0/0 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is 6173.5ba5.1234 (bia 6173.5ba5.1234)
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 24/255, rxload 102/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 1., loopback not set
Keepalive set (10 sec)
Full Duplex, 100Mbps, media type is RJ45
output flow-control is unsupported, input flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output 00:00:03, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/2 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 120632 bits/sec, 2 packets/sec
5 minute output rate 232021 bits/sec, 0 packets/sec
11715475 packets input, 2859109312 bytes, 0 no buffer
Received 195937 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 39113 multicast, 0 pause input
12065127 packets output, 1764633059 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
24466 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
1 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
Adjusting The Load Interval
The total load on a given interface can be measured by a the txload/255 + rxload/255 together never exceeding 255 or 100% of the overall interface. For example lets say we had an interface that was completely saturated at 100% capacity over a given period of time. Let’s say that during this given period of time the rxload was at 124/255 or 49% of the received interface utilization. Due to the fact that the interface is currently at 100% capacity this would mean that the txload would have to be ( 255 – 124 = 131 ) 131/255 or 51% of the total transmit interface utilization.
We can see from the above that the interface bandwidth is 100,000. A quick way to convert to either kbps or mbps
- Input Rate: 120632 / 1000 = kbps
- Input Rate: 120632 / 10000 = mbps
- Output Rate: 232021 / 1000 = kbps
- Output Rate: 232021 / 10000 = mbps
So for example if we were to our attention on the load interval itself…
Router#show interface GigabitEthernet0/0 | include load reliability 255/255, txload 18/255, rxload 98/255 Router#
With the current txload at 18, and the rxload at 98 the total interface utilization would 116/255 or 45% capacity.
Converting Bits & Megabits
- Megabits = Bits / 1,048,576
- Bits = Megabits * 1,048,576
Now lets focus on the load interval from the above GigabitEhternet0/0 interface.
Router#show interface gigabitethernet0/0 | include minute 5 minute input rate 23700 bits/sec, 2 packets/sec 5 minute output rate 12361 bits/sec, 0 packets/sec Router#
As we can see from the above output the default load interval is set at 5 minutes. This is typical of most if not all Cisco interfaces whether it be Serial or Ethernet. The default interval of 5 minute isn’t always the best setting when your trying to calculate the current overall bandwidth utilization. Fortunately this can be adjusted to meet your needs.
Router#configure terminal Router(config)#interface gigabitethernet0/0 Router(config-if)#load-interval 30 Router(config-if)#end Router#
Now lets take a look at the overall input, and output rate after the change.
Router#show interface gigabitethernet0/0 | include second 30 second input rate 423700 bits/sec, 2 packets/sec 30 second output rate 182361 bits/sec, 0 packets/sec Router#
I hope you found this post on TX & RX loads helpful and informative. Be sure to let me know what you think by leaving suggestions, and feedback in the comments section below. You can find out more about these and other articles be checking out recent posts and archives. To learn more about me be sure to check out the About page. And as always thanks again for visiting The Packet.
