Introduction
Output drops are a result of the traffic rate exceeding the maximum bandwidth specification of a given interface. Given that this is normally an outcome to interface congestion the following steps explain the commands used to clarify the total interface usage in both terms of Mbits and overall utilization.
Output Drop Totals
To confirm the total drops of a particular port the following command is run:
switch#sh int fa0/1 | in drop|bits
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 142478
5 minute input rate 1079000 bits/sec, 5524 packets/sec
5 minute output rate 8688000 bits/sec, 9018 packets/sec
We can also see the interface errors using the following command. The output errors are report here as OutDiscards.
switch#show interface FastEthernet0/1 counters errors
Port Align-Err FCS-Err Xmit-Err Rcv-Err UnderSize OutDiscards
Fa0/1 0 0 0 0 0 179107
Port Single-Col Multi-Col Late-Col Excess-Col Carri-Sen Runts Giants
Fa0/1 0 0 0 0 0 0 0
Changing Load-Intervals
As you can see from the previous section the load-intervals are configured to 5 minute intervals. To obtain a clearer view of the total throughput of a given interface the load-interval can be reduced to a lower value.
Below we change the load-interval to 30 secs:
switch(config)#interface FastEthernet0/1
switch(config-if)#load-interval 30
switch#sh int fa0/1 | in drop|bits
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 142478
30 second input rate 10079000 bits/sec, 5524 packets/sec
30 second output rate 86888000 bits/sec, 9018 packets/sec
Interface Ultization
To view the overall utilization (%) of an interface the following command is run:
switch#sh controllers fastEthernet 0/1 utilization
Receive Bandwidth Percentage Utilization : 13
Transmit Bandwidth Percentage Utilization : 100
Additional Errors
To display further details of the traffic that has transversed the interface the following command is run :
switch#sh controllers ethernet-controller fastEthernet 0/1
Transmit FastEthernet0/1 Receive
1755650038 Bytes 550748297 Bytes
565241190 Unicast frames 3235647489 Unicast frames
19304109 Multicast frames 0 Multicast frames
3784939 Broadcast frames 671 Broadcast frames
0 Too old frames 550705353 Unicast bytes
0 Deferred frames 0 Multicast bytes
0 MTU exceeded frames 42944 Broadcast bytes
0 1 collision frames 0 Alignment errors
0 2 collision frames 0 FCS errors
0 3 collision frames 0 Oversize frames
0 4 collision frames 0 Undersize frames
0 5 collision frames 0 Collision fragments
0 6 collision frames
0 7 collision frames 1912867443 Minimum size frames
0 8 collision frames 3138104280 65 to 127 byte frames
0 9 collision frames 80595969 128 to 255 byte frames
0 10 collision frames 29329601 256 to 511 byte frames
0 11 collision frames 551146604 512 to 1023 byte frames
0 12 collision frames 1818571559 1024 to 1518 byte frames
0 13 collision frames 0 Overrun frames
0 14 collision frames 0 Pause frames
0 15 collision frames
0 Excessive collisions 0 Symbol error frames
0 Late collisions 0 Invalid frames, too large
0 VLAN discard frames 0 Valid frames, too large
0 Excess defer frames 0 Invalid frames, too small
2417481382 64 byte frames 0 Valid frames, too small
1021375875 127 byte frames
691455767 255 byte frames 0 Too old frames
562825073 511 byte frames 0 Valid oversize frames
292399558 1023 byte frames 0 System FCS error frames
4192727175 1518 byte frames 0 RxPortFifoFull drop frame
0 Too large frames
0 Good (1 coll) frames
0 Good (>1 coll) frames
Options
Unfortunately there are only 2 solutions to output drops. These are :
- Increase the interface speed.
- Reduce the traffic throughput.
Reference
http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a0080094791.shtml |
