136 lines
5.3 KiB
Bash
Executable File
136 lines
5.3 KiB
Bash
Executable File
#!/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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#
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# Usage:
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# ./scripts/verify-netem.sh <peer-ip> [interface] [loss_pct]
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#
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# peer-ip IP of the other machine (the simulator's IP when run on the CM5,
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# or the CM5's IP when run on the Mac).
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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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# 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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# 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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set -euo pipefail
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PEER="${1:-}"
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IFACE="${2:-eth0}"
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LOSS="${3:-5}"
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if [[ -z "$PEER" ]]; then
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echo "Usage: $0 <peer-ip> [interface] [loss_pct]"
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echo "Example: $0 192.168.1.42 eth0 5"
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exit 1
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fi
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if [[ -t 1 ]]; then
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BOLD=$'\033[1m'; DIM=$'\033[2m'; GREEN=$'\033[32m'; YELLOW=$'\033[33m'
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RED=$'\033[31m'; RESET=$'\033[0m'
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else
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BOLD=; DIM=; GREEN=; YELLOW=; RED=; RESET=
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fi
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step() { printf '\n%s» %s%s\n' "$BOLD" "$1" "$RESET"; }
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ok() { printf '%s ✓ %s%s\n' "$GREEN" "$1" "$RESET"; }
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warn() { printf '%s ! %s%s\n' "$YELLOW" "$1" "$RESET"; }
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fail() { printf '%s ✗ %s%s\n' "$RED" "$1" "$RESET"; }
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# Sanity: tc + ping + interface
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for cmd in tc ping ip; do
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command -v "$cmd" >/dev/null || { fail "missing: $cmd"; exit 1; }
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done
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ip link show "$IFACE" >/dev/null 2>&1 || { fail "interface $IFACE not found"; exit 1; }
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# Print the route to the peer so the user can see which iface the kernel
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# actually uses — if it's not $IFACE, the netem rule won't apply.
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step "Route to peer $PEER"
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ROUTE_OUT="$(ip route get "$PEER" 2>&1 || true)"
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printf ' %s\n' "$ROUTE_OUT"
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ROUTE_IFACE="$(echo "$ROUTE_OUT" | awk '/dev/ {for(i=1;i<=NF;i++) if($i=="dev"){print $(i+1); exit}}')"
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if [[ -n "$ROUTE_IFACE" && "$ROUTE_IFACE" != "$IFACE" ]]; then
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warn "kernel routes $PEER via '$ROUTE_IFACE' but you're shaping '$IFACE'."
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warn "the netem rule will have NO effect on this peer's traffic."
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fi
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# State BEFORE
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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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# Apply netem
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step "Applying netem loss ${LOSS}% on $IFACE (egress)"
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sudo tc qdisc del dev "$IFACE" 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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# Trap to clean up on any exit path
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cleanup() {
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step "Removing netem qdisc from $IFACE"
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sudo tc qdisc del dev "$IFACE" root 2>/dev/null || true
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ok "qdisc removed; $IFACE back to default"
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}
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trap cleanup EXIT INT TERM
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# State AFTER install
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step "Current qdisc on $IFACE (after netem applied)"
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sudo tc qdisc show dev "$IFACE" | sed 's/^/ /'
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# Ping the peer and parse loss
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step "Pinging $PEER with 100 echoes (egress goes through netem)"
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PING_OUT="$(ping -c 100 -i 0.05 -W 1 "$PEER" 2>&1 || true)"
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echo "$PING_OUT" | tail -3 | sed 's/^/ /'
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# Parse "X% packet loss" — works on both Linux and macOS ping output.
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OBSERVED="$(echo "$PING_OUT" | grep -oE '[0-9.]+% packet loss' | head -1 | awk '{print $1}' | tr -d '%')"
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if [[ -z "$OBSERVED" ]]; then
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fail "could not parse ping output"
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exit 1
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fi
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# Sanity bracket: configured loss is ±3 percentage points absolute is fine for n=100.
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ABS_DELTA=$(awk -v o="$OBSERVED" -v l="$LOSS" 'BEGIN{d=o-l; if(d<0)d=-d; printf "%.1f", d}')
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step "Result"
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printf ' configured: %s%%\n observed: %s%%\n |delta|: %s pp\n' "$LOSS" "$OBSERVED" "$ABS_DELTA"
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if awk -v o="$OBSERVED" -v l="$LOSS" 'BEGIN{exit !(o > l*0.4 && o < l*2.0 + 3)}'; then
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ok "loss is being applied in the egress direction of $IFACE"
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else
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fail "observed loss ($OBSERVED%) does not match configured ($LOSS%)"
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warn "either the qdisc isn't routing as expected, or the kernel's netem"
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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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