netem ratelimit stops limiting rate after short time and restores to default
I have experienced a couple of times that netem stops working when I apply qdisc. This happened with both rate limit as well as loss.
For example, consider a scenario: Internet <------>(eth1) A (eth2)<------> (eth3)B
PC A is connected to an internet access point via ethernet port eth1. PC B is connected to PC A via port eth2 of PC A. So, basically, PC A is a bridge that I configure using OvS. I apply netem rule on eth2 and expect it to be reflected on PC B.
Now, in PC A, I applied a rate limit on eth2 of 30Mbps with a limit of 1000 using the command:
tc qdisc add dev eth2 root handle 1:0 netem rate 30000kbit limit 1000
Then I ran the iperf3 server on PC B and test the bandwidth by running the iperf3 client on a different PC (say 'C' that is connected to the network). The iperf3 result is:
[ 4] local xx.xx.xx.xx port 54838 connected to yy.yy.yy.yy port 5009
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 3.92 MBytes 32.8 Mbits/sec 0 185 KBytes
[ 4] 1.00-2.00 sec 3.50 MBytes 29.4 Mbits/sec 0 210 KBytes
[ 4] 2.00-3.00 sec 3.50 MBytes 29.4 Mbits/sec 0 210 KBytes
[ 4] 3.00-4.00 sec 3.38 MBytes 28.3 Mbits/sec 0 210 KBytes
[ 4] 4.00-5.00 sec 3.50 MBytes 29.4 Mbits/sec 0 210 KBytes
[ 4] 5.00-6.00 sec 3.38 MBytes 28.3 Mbits/sec 0 210 KBytes
[ 4] 6.00-7.00 sec 3.50 MBytes 29.4 Mbits/sec 0 210 KBytes
[ 4] 7.00-8.00 sec 3.50 MBytes 29.4 Mbits/sec 0 210 KBytes
[ 4] 8.00-9.00 sec 65.6 MBytes 550 Mbits/sec 142 210 KBytes
[ 4] 9.00-10.00 sec 109 MBytes 918 Mbits/sec 0 210 KBytes
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 203 MBytes 170 Mbits/sec 142 sender
[ 4] 0.00-10.00 sec 203 MBytes 170 Mbits/sec receiver
Initially, I am getting around 30Mbps but in the last two runs, the throughput is much higher than 30Mbps. I tried iperf3 again multiple times. Then it was fine. Why netem has this inconsistent behavior?
Another example where I cap rate to 50Mbps, the first iperf3 gave correct rate-limiting but one the second iperf3 attempt I got the inconsistent rate-limiting (as shown below):
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 6.05 MBytes 50.8 Mbits/sec 0 210 KBytes
[ 4] 1.00-2.00 sec 5.75 MBytes 48.2 Mbits/sec 0 210 KBytes
[ 4] 2.00-3.00 sec 5.75 MBytes 48.2 Mbits/sec 0 210 KBytes
[ 4] 3.00-4.00 sec 5.75 MBytes 48.2 Mbits/sec 0 210 KBytes
[ 4] 4.00-5.00 sec 29.8 MBytes 250 Mbits/sec 143 210 KBytes
[ 4] 5.00-6.00 sec 110 MBytes 920 Mbits/sec 0 210 KBytes
[ 4] 6.00-7.00 sec 109 MBytes 914 Mbits/sec 0 210 KBytes
[ 4] 7.00-8.00 sec 109 MBytes 915 Mbits/sec 0 210 KBytes
[ 4] 8.00-9.00 sec 109 MBytes 914 Mbits/sec 0 210 KBytes
[ 4] 9.00-10.00 sec 109 MBytes 914 Mbits/sec 0 210 KBytes
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 599 MBytes 502 Mbits/sec 143 sender
[ 4] 0.00-10.00 sec 598 MBytes 502 Mbits/sec receiver
After the fourth run, it appears that netem ratelimit is simply gone and the network is back to its default rate.
I have seen this behaviour when I introduce loss using netem. Please, any help to fix this or explain this inconsistent netem behaviour would be helpful. Thanks.
Comments
-
I found a solution to this problem.
PC A is the one acting as a bridge for two ethernet connections. Once we set OvS bridge, the internet is no longer available on PC A. By default, the OS (ubuntu 20 in this case) is configured to attempt connecting to the internet automatically after regular intervals on both eth1 and eth2. Because of OvS configuration, the connection attempt is bound to fail. After the failure notification, the qdisc is removed on the network devices. This results in the iperf3 behavior as described in the question.
The fix is simple, just go to the network settings and disable auto-connect on both eth1 and eth2, and save the setting. Once done, netem works fine.
Hope this helps those who may face this issue in the future.
0
Categories
- 10.1K All Categories
- 35 LFX Mentorship
- 88 LFX Mentorship: Linux Kernel
- 501 Linux Foundation Boot Camps
- 278 Cloud Engineer Boot Camp
- 103 Advanced Cloud Engineer Boot Camp
- 47 DevOps Engineer Boot Camp
- 40 Cloud Native Developer Boot Camp
- 2 Express Training Courses
- 2 Express Courses - Discussion Forum
- 1.7K Training Courses
- 17 LFC110 Class Forum
- 4 LFC131 Class Forum
- 19 LFD102 Class Forum
- 148 LFD103 Class Forum
- 12 LFD121 Class Forum
- 61 LFD201 Class Forum
- LFD210 Class Forum
- 1 LFD213 Class Forum - Discontinued
- 128 LFD232 Class Forum
- 23 LFD254 Class Forum
- 566 LFD259 Class Forum
- 100 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- 1 LFS145 Class Forum
- 22 LFS200 Class Forum
- 739 LFS201 Class Forum
- 1 LFS201-JP クラス フォーラム
- 1 LFS203 Class Forum
- 44 LFS207 Class Forum
- 298 LFS211 Class Forum
- 53 LFS216 Class Forum
- 46 LFS241 Class Forum
- 40 LFS242 Class Forum
- 37 LFS243 Class Forum
- 10 LFS244 Class Forum
- 27 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- 131 LFS253 Class Forum
- 993 LFS258 Class Forum
- 10 LFS258-JP クラス フォーラム
- 87 LFS260 Class Forum
- 126 LFS261 Class Forum
- 31 LFS262 Class Forum
- 79 LFS263 Class Forum
- 15 LFS264 Class Forum
- 10 LFS266 Class Forum
- 17 LFS267 Class Forum
- 17 LFS268 Class Forum
- 21 LFS269 Class Forum
- 200 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- 212 LFW211 Class Forum
- 153 LFW212 Class Forum
- 899 Hardware
- 217 Drivers
- 74 I/O Devices
- 44 Monitors
- 115 Multimedia
- 208 Networking
- 101 Printers & Scanners
- 85 Storage
- 749 Linux Distributions
- 88 Debian
- 64 Fedora
- 14 Linux Mint
- 13 Mageia
- 24 openSUSE
- 133 Red Hat Enterprise
- 33 Slackware
- 13 SUSE Enterprise
- 355 Ubuntu
- 472 Linux System Administration
- 38 Cloud Computing
- 69 Command Line/Scripting
- Github systems admin projects
- 94 Linux Security
- 77 Network Management
- 107 System Management
- 49 Web Management
- 63 Mobile Computing
- 22 Android
- 27 Development
- 1.2K New to Linux
- 1.1K Getting Started with Linux
- 527 Off Topic
- 127 Introductions
- 213 Small Talk
- 19 Study Material
- 794 Programming and Development
- 262 Kernel Development
- 498 Software Development
- 922 Software
- 257 Applications
- 182 Command Line
- 2 Compiling/Installing
- 76 Games
- 316 Installation
- 52 All In Program
- 52 All In Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)