Collect UDP packets lost during iPerf test

Question

I'm testing my network infrastructure where I'm using iPerf and UDP protocol.

I'm using the following:

On the server side:

ubuntu@ip-172-0-1-11:~$ iperf -s -u

and the client side:

ubuntu@ip-172-2-1-10:~$iperf -c 172.0.1.11 -u -b 100m 

I understand that when more traffic than a link can handle is sent to a link, the interface to that link will end up dropping the packets destined for that link. However, I'm interested in collecting those packet loss rates. Is there a way to collect it?

I'm running Cacti an open-source, web-based network monitoring and graphing. SNMP server is enabled in the Cisco routers.

Router(config)#snmp-server community public RO 
Router(config)#snmp-server community private RW

I'm getting the collected data of the interfaces in the Cacti server. However, I want also to have packet loss data collected, too.

Edited part of the question

I added the In/Out Errors/Discarded Packets to the graphs' tree in Cacti. However, so far there is no data which is collected, it is always 0, and I can see from Iperf that there is packets loss, although there are data and graphs for the In/Out Bits graphs.

This the information I got from the interface:

{
"Cisco-IOS-XE-interfaces-oper:statistics": {
    "discontinuity-time": "2019-06-26T15:09:55.000005+00:00",
    "in-octets": "4140080366",
    "in-unicast-pkts": "5381499",
    "in-broadcast-pkts": "0",
    "in-multicast-pkts": "0",
    "in-discards": 0,
    "in-errors": 0,
    "in-unknown-protos": 0,
    "out-octets": 2579777476,
    "out-unicast-pkts": "13916798",
    "out-broadcast-pkts": "0",
    "out-multicast-pkts": "0",
    "out-discards": "2843",
    "out-errors": "0",
    "rx-pps": "5527",
    "rx-kbps": "34266",
    "tx-pps": "16523",
    "tx-kbps": "106588",
    "num-flaps": "0",
    "in-crc-errors": "0"
}

}

Apparently, there's no packet loss recorded in in-errors and out-errors which are both 0. However, sometimes I got packet loss from the Iperf report:

[  5] local 172.2.1.10 port 5001 connected with 172.0.1.11 port 43372
[  5]  0.0-842.3 sec  23.8 MBytes   237 Kbits/sec   0.250 ms    2/17008 (0.012%)
[  4] local 172.2.1.10 port 5001 connected with 172.0.1.11 port 43961
[  4]  0.0-857.3 sec  23.8 MBytes   233 Kbits/sec   0.548 ms    9/17008 (0.053%)
[  5] local 172.2.1.10 port 5001 connected with 172.0.1.11 port 51505
[  5]  0.0-872.4 sec  23.8 MBytes   229 Kbits/sec   0.260 ms    0/17008 (0%)

I really don't understand the reason for this packet loss.

P.S. in my network infrastructure, I'm running Segment Routing where I have 4 routers where the traffic flow might pass one router multiple times depends on the Segment Routing Explicit Path.

Answer 1

Depending on your Cacti version, we collect errors and discarded packets without any problems on Version 1.1.38.

Here's how we do it.

Select the tab Console, then extend Management and click devices.

In the device list, select the switch/router you want to get the information from.

Now under the selected device, click create graph for the device.

Now at bottom select the In/Out Errors/Discarded Packets in the roll-down menu, then select the interface, where you want to create the counter on. The click create.

That's basically how you do it. I assume you have added the device correctly to Cacti and setup SNMP correctly. Otherwise this wont work.

Please note that Cacti takes a bit of time before generating the graph. Several tests should give you data within a short time.