Jitter generation with netem is not working

Question

I am trying to simulate jitter in my network using netem. I am using the following command:

sudo tc qdisc add dev eno3 root netem delay 200ms 100ms

And this command the output of the ping to the other IP:

$ ping 10.82.96.254 -c 10
PING 10.82.96.254 (10.82.96.254) 56(84) bytes of data.
64 bytes from 10.82.96.254: icmp_seq=1 ttl=255 time=258 ms
64 bytes from 10.82.96.254: icmp_seq=2 ttl=255 time=233 ms
64 bytes from 10.82.96.254: icmp_seq=3 ttl=255 time=295 ms
64 bytes from 10.82.96.254: icmp_seq=6 ttl=255 time=260 ms
64 bytes from 10.82.96.254: icmp_seq=8 ttl=255 time=212 ms
64 bytes from 10.82.96.254: icmp_seq=4 ttl=255 time=4466 ms
64 bytes from 10.82.96.254: icmp_seq=5 ttl=255 time=4474 ms
64 bytes from 10.82.96.254: icmp_seq=7 ttl=255 time=4459 ms
64 bytes from 10.82.96.254: icmp_seq=9 ttl=255 time=4476 ms
64 bytes from 10.82.96.254: icmp_seq=10 ttl=255 time=4453 ms

--- 10.82.96.254 ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 9051ms
rtt min/avg/max/mdev = 212.173/2359.059/4476.181/2107.031 ms, pipe 5

Normally with this command I would expect the round trip time to varies between 100 and 300ms so these 4400ms replies are really surprising me. If I only generate time delay everything seems to be working OK:

$ ping 10.82.96.254 -c 10
PING 10.82.96.254 (10.82.96.254) 56(84) bytes of data.
64 bytes from 10.82.96.254: icmp_seq=1 ttl=255 time=202 ms
64 bytes from 10.82.96.254: icmp_seq=2 ttl=255 time=200 ms
64 bytes from 10.82.96.254: icmp_seq=3 ttl=255 time=200 ms
64 bytes from 10.82.96.254: icmp_seq=4 ttl=255 time=200 ms
64 bytes from 10.82.96.254: icmp_seq=5 ttl=255 time=202 ms
64 bytes from 10.82.96.254: icmp_seq=6 ttl=255 time=201 ms
64 bytes from 10.82.96.254: icmp_seq=7 ttl=255 time=201 ms
64 bytes from 10.82.96.254: icmp_seq=8 ttl=255 time=200 ms
64 bytes from 10.82.96.254: icmp_seq=9 ttl=255 time=200 ms
64 bytes from 10.82.96.254: icmp_seq=10 ttl=255 time=203 ms

--- 10.82.96.254 ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 9003ms
rtt min/avg/max/mdev = 200.365/201.286/203.059/1.013 ms

I am running Ubuntu 18.04 server image with all the packages up-to-date. I was using the same utility in 16.04 for generating network impairments and I think it was working fine on the previous Linux distribution 16.04LTS using the same hardware.

A small detail is that I am running a bridge between eno3 and eno4 and I am accessing the Linux server over eno1.

Answer 1

This appears to be a bug in the 4.15 kernel. In order to solve it, you need to update to 4.18 or downgrade the Linux Kernel. This is the description of the issue in Launchpad: link