netem and iproute2 with tc

traffic control of tc in linux and netem

on Alpine



add package	apk update apk add iproute2
	apk for alpine based on busybox
kernel module
load	modprobe sch_netem modprobe cls_u32
check	lsmod \| grep netem
permanent	Not needed !!!
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
+ 100 ms	tc qdisc add dev eth0 root netem delay 100ms
remote it	tc qdisc del dev eth0 root
packet loss
+ 10%	tc qdisc change dev eth0 root netem loss 10%
	tc qdisc del dev eth0 root
duplication
	sudo tc qdisc add dev eth0 root netem duplicate 10%

reordering
	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.
show
	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`.
	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)