Add iperf3 traffic generator for DC<->Campus gold VRF path

Host containers sit idle otherwise, leaving IPFabric ARP/MAC tables and
Grafana throughput graphs empty until someone manually generates traffic.

Refs #55

scripts/generate_traffic.sh

@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+# Generates DC<->Campus traffic over VRF gold using iperf3 (bundled in the
+# network-multitool image every host container runs), with a live
+# server/client bandwidth dashboard. Refs #55.
+set -euo pipefail
+
+DURATION="${1:?Usage: $0 <duration_seconds>}"
+if ! [[ "$DURATION" =~ ^[0-9]+$ ]] || [[ "$DURATION" -lt 1 ]]; then
+    echo "Duration must be a positive integer (seconds)" >&2
+    exit 1
+fi
+
+LAB_PREFIX="clab-arista-evpn-fabric"
+PORT=5301
+
+# server_name:server_ip:client_name  — gold VRF pairs, stitched EVPN
+# Type-5 path DC -> Core -> Campus (see README Host Addressing table)
+PAIRS=(
+    "dc-server2:10.34.34.102:campus-host1"
+    "dc-server4:10.78.78.104:campus-host2"
+)
+
+WORKDIR="$(mktemp -d)"
+CLIENT_PIDS=()
+
+cleanup() {
+    for pid in "${CLIENT_PIDS[@]:-}"; do
+        kill "$pid" >/dev/null 2>&1 || true
+    done
+    for pair in "${PAIRS[@]}"; do
+        IFS=':' read -r server _ _ <<<"$pair"
+        docker exec "${LAB_PREFIX}-${server}" pkill -f "iperf3 -s -p ${PORT}" >/dev/null 2>&1 || true
+    done
+    rm -rf "$WORKDIR"
+}
+trap cleanup EXIT INT TERM
+
+echo "Starting iperf3 servers..."
+for pair in "${PAIRS[@]}"; do
+    IFS=':' read -r server server_ip _ <<<"$pair"
+    docker exec -d "${LAB_PREFIX}-${server}" iperf3 -s -p "$PORT"
+done
+sleep 1
+
+echo "Starting iperf3 clients for ${DURATION}s..."
+for pair in "${PAIRS[@]}"; do
+    IFS=':' read -r server server_ip client <<<"$pair"
+    logfile="${WORKDIR}/${client}.log"
+    docker exec "${LAB_PREFIX}-${client}" iperf3 -c "$server_ip" -p "$PORT" \
+        -t "$DURATION" -i 1 --forceflush -f m >"$logfile" 2>&1 &
+    CLIENT_PIDS+=("$!")
+done
+
+for ((elapsed = 0; elapsed <= DURATION; elapsed++)); do
+    clear
+    echo "EVPN/VXLAN lab traffic generator — ${elapsed}/${DURATION}s"
+    echo
+    echo "Servers (iperf3 -s):"
+    for pair in "${PAIRS[@]}"; do
+        IFS=':' read -r server server_ip _ <<<"$pair"
+        echo "  ${server} (${server_ip}:${PORT})"
+    done
+    echo
+    echo "Clients (live bandwidth):"
+    for pair in "${PAIRS[@]}"; do
+        IFS=':' read -r server server_ip client <<<"$pair"
+        logfile="${WORKDIR}/${client}.log"
+        last_line="$(grep -E 'Mbits/sec' "$logfile" 2>/dev/null | tail -1 || true)"
+        bw="$(sed -E 's/.*[[:space:]]([0-9.]+ Mbits\/sec).*/\1/' <<<"$last_line")"
+        [[ -z "$last_line" ]] && bw="waiting..."
+        printf "  %-13s -> %-13s : %s\n" "$client" "$server" "$bw"
+    done
+    sleep 1
+done
+
+wait "${CLIENT_PIDS[@]}" 2>/dev/null || true
+
+echo
+echo "Done. Summary:"
+for pair in "${PAIRS[@]}"; do
+    IFS=':' read -r server _ client <<<"$pair"
+    logfile="${WORKDIR}/${client}.log"
+    summary="$(grep -E 'receiver' "$logfile" 2>/dev/null || true)"
+    echo "  ${client} -> ${server}: ${summary:-no data}"
+done