ipv6_path_drift_watch.sh

#!/usr/bin/env bash

set -euo pipefail

# ipv6_path_drift_watch.sh
# Watches IPv6 path changes to one or more targets across repeated trace samples.

usage() {
  cat <<'EOF'
Usage: ./ipv6_path_drift_watch.sh [options]

Options:
  --target HOST          IPv6 host/address to trace (repeatable)
  --samples N            Number of trace rounds (default: 5)
  --interval SEC         Seconds between rounds (default: 3)
  --max-hops N           Maximum hops (default: 20)
  --wait SEC             Per-probe wait seconds (default: 2)
  --strict               Exit non-zero when path drift is detected
  -h, --help             Show help

Exit codes:
  0 = no drift (or drift in non-strict mode)
  2 = strict mode and path drift detected
EOF
}

TARGETS=("2606:4700:4700::1111" "2001:4860:4860::8888")
SAMPLES=5
INTERVAL=3
MAX_HOPS=20
WAIT=2
STRICT=false

while [[ $# -gt 0 ]]; do
  case "$1" in
    --target) TARGETS+=("$2"); shift 2 ;;
    --samples) SAMPLES="$2"; shift 2 ;;
    --interval) INTERVAL="$2"; shift 2 ;;
    --max-hops) MAX_HOPS="$2"; shift 2 ;;
    --wait) WAIT="$2"; shift 2 ;;
    --strict) STRICT=true; shift ;;
    -h|--help) usage; exit 0 ;;
    *) echo "Unknown option: $1"; usage; exit 1 ;;
  esac
done

if [[ "${#TARGETS[@]}" -gt 2 ]]; then
  TARGETS=("${TARGETS[@]:2}")
fi

trace_once() {
  local target="$1"
  local raw

  if command -v traceroute >/dev/null 2>&1; then
    raw=$(traceroute -6 -n -q 1 -w "$WAIT" -m "$MAX_HOPS" "$target" 2>/dev/null || true)
    printf '%s\n' "$raw" | awk '/^[[:space:]]*[0-9]+[[:space:]]/ {print $2}' | sed '/^$/d'
    return
  fi

  if command -v tracepath >/dev/null 2>&1; then
    raw=$(tracepath -6 -n -m "$MAX_HOPS" "$target" 2>/dev/null || true)
    printf '%s\n' "$raw" | awk '/^[[:space:]]*[0-9]+:/ {print $2}' | sed '/^$/d'
    return
  fi

  echo "NO_TRACE_TOOL"
}

echo "IPv6 path drift watch timestamp: $(date -Iseconds)"
echo "targets=${TARGETS[*]} samples=$SAMPLES interval=${INTERVAL}s max_hops=$MAX_HOPS strict_mode=$STRICT"
echo

if ! command -v traceroute >/dev/null 2>&1 && ! command -v tracepath >/dev/null 2>&1; then
  echo "Neither traceroute nor tracepath is installed"
  exit 1
fi

declare -A baseline_path
drift_count=0

for ((sample=1; sample<=SAMPLES; sample++)); do
  echo "=== Sample $sample/$SAMPLES ==="
  for target in "${TARGETS[@]}"; do
    hops=$(trace_once "$target")
    path=$(printf '%s\n' "$hops" | paste -sd '>' -)
    [[ -z "$path" ]] && path="NO_PATH"

    if [[ -z "${baseline_path[$target]:-}" ]]; then
      baseline_path[$target]="$path"
      status="BASELINE"
    elif [[ "${baseline_path[$target]}" == "$path" ]]; then
      status="STABLE"
    else
      status="DRIFT"
      ((drift_count+=1))
    fi

    echo "target=$target status=$status"
    echo "path=$path"
    echo
  done

  if [[ "$sample" -lt "$SAMPLES" ]]; then
    sleep "$INTERVAL"
  fi
done

echo "Summary: drift_count=$drift_count strict_mode=$STRICT"
if [[ "$STRICT" == true && "$drift_count" -gt 0 ]]; then
  exit 2
fi

exit 0