Update to scripts to better handle netem
This commit is contained in:
Valère Plantevin
@@ -1,6 +1,6 @@
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#!/usr/bin/env bash
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# scripts/verify-netem.sh — confirm tc-netem is actually applying loss, in
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# the direction you think it is.
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# the direction(s) you think it is.
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#
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# Usage:
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# ./scripts/verify-netem.sh <peer-ip> [interface] [loss_pct]
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@@ -10,26 +10,32 @@
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# interface Interface tc-netem is applied to. Default: eth0.
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# loss_pct Loss percentage to apply. Default: 5.
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#
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# Modes (env var):
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# BIDI=0 (default) Egress-only. Shapes outgoing traffic from <interface>.
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# Use a single ping from this host to verify.
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# BIDI=1 Bidirectional via ifb ingress redirect. Shapes BOTH
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# outgoing AND incoming traffic on <interface>. Pings
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# run from THIS host verify egress; the script also
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# prompts you to ping back FROM THE PEER to verify
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# ingress (the script holds the qdisc up until you press
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# Enter, then tears everything down).
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#
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# What it does:
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# 1. Prints the current qdisc state (sanity check before).
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# 2. Applies `netem loss <loss_pct>%` on egress of <interface>.
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# 2. Applies the configured netem loss (egress, or egress + ingress).
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# 3. Re-prints the qdisc state (confirms the rule is installed).
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# 4. Sends 100 ICMP echo requests to <peer-ip> and reports the observed loss.
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# 5. Removes the qdisc on exit (trap), even on Ctrl-C.
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#
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# IMPORTANT direction caveat:
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# tc qdisc rules apply to EGRESS only. If you run this on the CM5, it shapes
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# CM5 → peer traffic. The peer → CM5 direction is unaffected. To drop traffic
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# coming INTO this machine, you must either:
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# (a) run netem on the SENDER side, or
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# (b) attach an ifb (intermediate functional block) device for ingress.
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# See the "Bidirectional loss" section in the script footer for the ifb recipe.
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# 5. BIDI=1 only: waits for you to run `ping -c 100 <this-host>` from the
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# peer machine and report what it saw.
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# 6. Removes the qdiscs (and brings ifb0 down) on exit, even on Ctrl-C.
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set -euo pipefail
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PEER="${1:-}"
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IFACE="${2:-eth0}"
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LOSS="${3:-5}"
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BIDI="${BIDI:-0}"
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IFB_DEV="${IFB_DEV:-ifb0}"
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if [[ -z "$PEER" ]]; then
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echo "Usage: $0 <peer-ip> [interface] [loss_pct]"
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@@ -69,23 +75,57 @@ fi
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step "Current qdisc on $IFACE (before)"
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sudo tc qdisc show dev "$IFACE" | sed 's/^/ /'
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# If bidi, ensure ifb device is up before installing qdiscs.
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if [[ "$BIDI" -eq 1 ]]; then
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step "Bringing up $IFB_DEV (BIDI mode)"
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sudo modprobe ifb numifbs=1 2>/dev/null || true
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if ! ip link show "$IFB_DEV" >/dev/null 2>&1; then
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fail "ifb device $IFB_DEV not present after modprobe; cannot run BIDI mode"
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exit 1
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fi
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sudo ip link set "$IFB_DEV" up
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ok "$IFB_DEV is up"
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fi
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# Apply netem
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step "Applying netem loss ${LOSS}% on $IFACE (egress)"
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if [[ "$BIDI" -eq 1 ]]; then
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step "Applying netem loss ${LOSS}% on $IFACE (egress + ingress via $IFB_DEV)"
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else
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step "Applying netem loss ${LOSS}% on $IFACE (egress only)"
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fi
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sudo tc qdisc del dev "$IFACE" root 2>/dev/null || true
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sudo tc qdisc del dev "$IFACE" ingress 2>/dev/null || true
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[[ "$BIDI" -eq 1 ]] && sudo tc qdisc del dev "$IFB_DEV" root 2>/dev/null || true
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sudo tc qdisc add dev "$IFACE" root netem loss "${LOSS}%"
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ok "qdisc installed"
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if [[ "$BIDI" -eq 1 ]]; then
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sudo tc qdisc add dev "$IFACE" handle ffff: ingress
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sudo tc filter add dev "$IFACE" parent ffff: protocol all u32 \
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match u32 0 0 action mirred egress redirect dev "$IFB_DEV"
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sudo tc qdisc add dev "$IFB_DEV" root netem loss "${LOSS}%"
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fi
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ok "qdisc(s) installed"
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# Trap to clean up on any exit path
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cleanup() {
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step "Removing netem qdisc from $IFACE"
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step "Removing netem qdiscs"
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sudo tc qdisc del dev "$IFACE" root 2>/dev/null || true
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ok "qdisc removed; $IFACE back to default"
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sudo tc qdisc del dev "$IFACE" ingress 2>/dev/null || true
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if [[ "$BIDI" -eq 1 ]]; then
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sudo tc qdisc del dev "$IFB_DEV" root 2>/dev/null || true
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sudo ip link set "$IFB_DEV" down 2>/dev/null || true
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fi
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ok "qdiscs removed; $IFACE back to default"
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}
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trap cleanup EXIT INT TERM
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# State AFTER install
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step "Current qdisc on $IFACE (after netem applied)"
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step "Current qdisc state (after netem applied)"
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sudo tc qdisc show dev "$IFACE" | sed 's/^/ /'
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if [[ "$BIDI" -eq 1 ]]; then
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sudo tc qdisc show dev "$IFB_DEV" | sed 's/^/ /'
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echo " filter on $IFACE ingress:"
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sudo tc filter show dev "$IFACE" parent ffff: 2>/dev/null | sed 's/^/ /'
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fi
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# Ping the peer and parse loss
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step "Pinging $PEER with 100 echoes (egress goes through netem)"
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@@ -112,24 +152,17 @@ else
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warn "build doesn't include the loss module. Check 'modprobe sch_netem'."
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fi
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# ---------------------------------------------------------------------------
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# Bidirectional loss (info — not run by this script)
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# ---------------------------------------------------------------------------
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# tc qdisc shapes egress. To drop INCOMING traffic on the CM5 (e.g. T1
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# datagrams flowing from the Mac), redirect ingress to an ifb device and
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# shape that:
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#
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# sudo modprobe ifb numifbs=1
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# sudo ip link set ifb0 up
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# sudo tc qdisc add dev $IFACE handle ffff: ingress
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# sudo tc filter add dev $IFACE parent ffff: protocol all u32 \
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# match u32 0 0 action mirred egress redirect dev ifb0
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# sudo tc qdisc add dev ifb0 root netem loss 5%
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#
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# Clean up:
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# sudo tc qdisc del dev $IFACE ingress 2>/dev/null
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# sudo tc qdisc del dev ifb0 root 2>/dev/null
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# sudo ip link set ifb0 down
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#
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# Or — simpler — apply netem on BOTH ends with their respective egress qdiscs
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# (run this script with the same loss_pct on the Mac too).
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if [[ "$BIDI" -eq 1 ]]; then
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step "Now verify the INGRESS direction"
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THIS_IP="$(ip -4 addr show dev "$IFACE" | awk '/inet / {print $2}' | cut -d/ -f1 | head -1)"
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cat <<EOF
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From the peer machine, run:
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ping -c 100 -i 0.05 ${THIS_IP:-<this host\'s IP on $IFACE>}
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You should see ~${LOSS}% packet loss in the peer's ping output. That confirms
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ingress shaping is dropping packets arriving here on $IFACE.
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Press Enter when done to tear everything down.
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EOF
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read -r _ </dev/tty || true
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fi
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