traffic control of tc in linux and netem
tc qdisc Linux Traffic Control or tc
| Test |
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| tc qdisc change dev eth0 root netem loss 10% delay 100ms
alpine:~# tc qdisc show
qdisc netem 8003: dev eth0 root refcnt 2 limit 1000 delay 100ms loss 10%
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| sudo -i for i in {1..10}; do echo "Ping attempt $i:"; ping -c 100 -f -q 8.8.8.8; echo -e "\n"; done |
| Result | |
| on Alpine |
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| add package | apk update
apk add iproute2 |
| apk for alpine based on busybox |
| kernel module |
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| load | modprobe sch_netem
modprobe cls_u32 |
| check | lsmod | grep netem |
| permanent | Not needed !!! |
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| create file | vi /etc/local.d/netem.start tc qdisc change dev eth0 root netem xxxxxxxx |
| chmod +x /etc/local.d/netem.start
rc-update add local |
| latency |
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| + 100 ms | tc qdisc add dev eth0 root netem delay 100ms |
| remote it | tc qdisc del dev eth0 root |
| packet loss |
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| + 10% | tc qdisc add dev eth0 root netem loss 10% |
| tc qdisc change dev eth0 root netem loss 10% |
| tc qdisc del dev eth0 root |
| duplication |
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| sudo tc qdisc add dev eth0 root netem duplicate 10% |
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| reordering |
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| sudo tc qdisc add dev eth0 root netem reorder 25% 50% |
| reorder 25%: Specifies that 25% of packets will be reordered.50%: Correlation value, meaning that once reordering starts, there is a 50% chance it continues.
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| show |
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| alpine:~# tc qdisc show
qdisc noqueue 0: dev lo root refcnt 2
qdisc netem 8001: dev eth0 root refcnt 2 limit 1000 loss 10%
qdisc pfifo_fast 0: dev eth1 root refcnt 2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 |
| qdisc netem 8001: dev eth0 root refcnt 2 limit 1000 loss 10%
qdisc netem: A qdisc implementing network emulation. This is commonly used to simulate network conditions like delay, loss, duplication, or reordering.8001:: A unique handle identifying this qdisc.dev eth0: Applied to the eth0 interface.root: This is the root qdisc for the eth0 interface.refcnt 2: Two users or instances depend on this qdisc.limit 1000: Specifies the maximum number of packets that can be queued.loss 10%: Simulates a 10% packet loss rate on traffic passing through eth0.
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| qdisc pfifo_fast 0: dev eth1 root refcnt 2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc pfifo_fast: A default qdisc for many Linux setups, implementing a priority FIFO (First In, First Out) queue.0:: A handle identifying this qdisc.dev eth1: Applied to the eth1 interface.root: This is the root qdisc for the eth1 interface.refcnt 2: Two users or instances rely on this qdisc.bands 3: Traffic is divided into 3 bands (queues), each with a different priority. ( Band 0=HightP, 1=MPriority and 2=LowP )priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1:- Defines how packets are classified into these bands based on their Type of Service (ToS) field.
- Lower-priority packets are placed in higher-numbered bands, and higher-priority packets (like VoIP) are placed in lower-numbered bands.
Each number corresponds to a ToS value (0–7) and maps it to one of the priority bands: 0: Band 1 (lower priority)1: Band 2 (medium priority)2: Band 2 (medium priority)3: Band 2 (medium priority)4: Band 1 (lower priority)5: Band 2 (medium priority)6: Band 0 (high priority)7: Band 0 (high priority)
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