386 lines
14 KiB
Bash
386 lines
14 KiB
Bash
#!/usr/bin/env bash
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#
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# detect_bridge.sh
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#
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# Detect whether there is a switch / Linux bridge between THIS host and a target host.
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# - Usage: sudo ./detect_bridge.sh <target-ip-or-hostname> [interface]
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# - Optional flags:
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# --mac-spoof (runs an optional MAC-change test; disabled by default)
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#
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# Requires: bash, ip, ping, tcpdump, ethtool, arping, awk, grep, sed, date, awk, timeout
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# lldpctl if available (script will check).
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#
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# Notes:
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# - Many methods require root (tcpdump, ethtool, arping). Run with sudo.
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# - The script attempts safe tests first. MAC spoofing is optional and may disrupt traffic.
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# - The script prints a summary and confidence estimate at the end.
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#
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set -euo pipefail
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IFS=$'\n\t'
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TARGET="$1"
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IFACE="${2:-}"
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MAC_SPOOF=false
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# parse optional flags
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for arg in "$@"; do
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if [ "$arg" = "--mac-spoof" ]; then
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MAC_SPOOF=true
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fi
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done
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# helper: detect default interface to reach target
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detect_iface() {
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if [ -n "$IFACE" ]; then
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echo "$IFACE"
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return 0
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fi
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# Use 'ip route get' to find outgoing interface
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if route_info=$(ip route get "$TARGET" 2>/dev/null); then
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# route_info often contains "dev <iface>"
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dev=$(echo "$route_info" | awk '{for(i=1;i<=NF;i++){if($i=="dev"){print $(i+1);exit}}}')
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if [ -n "$dev" ]; then
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echo "$dev"
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return 0
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fi
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fi
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# fallback to first non-loopback up interface
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for dev in $(ls /sys/class/net); do
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if [ "$dev" != "lo" ] && [ -f "/sys/class/net/$dev/operstate" ] && grep -q "up" "/sys/class/net/$dev/operstate"; then
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echo "$dev"
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return 0
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fi
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done
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echo "eth0"
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}
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if ! command -v ip >/dev/null 2>&1; then
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echo "This script requires 'ip' (iproute2). Aborting." >&2
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exit 1
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fi
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IFACE=$(detect_iface)
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echo "Target: $TARGET"
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echo "Interface: $IFACE"
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echo
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# ensure we can resolve target ip
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TARGET_IP=""
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if [[ "$TARGET" =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
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TARGET_IP="$TARGET"
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else
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if ! TARGET_IP=$(getent hosts "$TARGET" | awk '{print $1}' | head -n1); then
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echo "Failed to resolve target '$TARGET'." >&2
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exit 1
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fi
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fi
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echo "Resolved target IP: $TARGET_IP"
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echo
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# check for required commands and print warnings for optional commands
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REQ_CMDS=(ip ping awk grep sed date)
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for c in "${REQ_CMDS[@]}"; do
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if ! command -v "$c" >/dev/null 2>&1; then
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echo "Missing required command: $c" >&2
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exit 1
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fi
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done
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# optional commands
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HAS_TCPDUMP=false
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HAS_ETHTOOL=false
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HAS_ARPING=false
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HAS_LLDPC=false
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HAS_TRACEROUTE=false
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if command -v tcpdump >/dev/null 2>&1; then HAS_TCPDUMP=true; fi
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if command -v ethtool >/dev/null 2>&1; then HAS_ETHTOOL=true; fi
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if command -v arping >/dev/null 2>&1; then HAS_ARPING=true; fi
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if command -v lldpctl >/dev/null 2>&1; then HAS_LLDPC=true; fi
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if command -v traceroute >/dev/null 2>&1; then HAS_TRACEROUTE=true; fi
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echo "Tool availability:"
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echo " tcpdump: $HAS_TCPDUMP"
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echo " ethtool: $HAS_ETHTOOL"
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echo " arping: $HAS_ARPING"
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echo " lldpctl: $HAS_LLDPC"
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echo " traceroute: $HAS_TRACEROUTE"
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echo
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# helper to run a command with a nice header
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run_header() {
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echo
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echo "===== $1 ====="
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}
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# 1) interface->master check (fast & safe)
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run_header "Interface master / bridge hint (ip link)"
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ip link show dev "$IFACE" | sed -n '1,4p'
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# Look for "master <bridge>" or "brd"
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master=$(ip link show dev "$IFACE" 2>/dev/null | tr '\n' ' ' | sed 's/.*master \([^ ]*\).*/\1/;t;d')
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if [ -n "$master" ]; then
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echo "Interface reports master: $master -> This interface is enslaved to a bridge on this host (local bridge)."
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else
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echo "No 'master' shown; interface is not a local bridge slave (or not reported)."
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fi
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# 2) check /sys/class/net/<if>/bridge (exists only when this host has a bridge device)
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run_header "Check local bridge sysfs"
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if [ -d "/sys/class/net/$IFACE/bridge" ]; then
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echo "/sys/class/net/$IFACE/bridge exists -> this host has a bridge device attached to $IFACE (local)."
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else
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echo "No /sys/class/net/$IFACE/bridge -> local host is not the bridge owner for this interface."
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fi
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# 3) LLDP via lldpctl (if installed)
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if $HAS_LLDPC; then
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run_header "LLDP via lldpctl (if lldpd installed) -- shows neighbor(s) when available"
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echo "(running: lldpctl -f keyvalue on $IFACE)"
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sudo lldpctl -f keyvalue "$IFACE" 2>/dev/null || echo "lldpctl produced no output or isn't running for $IFACE."
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else
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run_header "LLDP: lldpctl not installed"
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echo "lldpctl not installed. You can install lldpd (Debian/Ubuntu: apt install lldpd) and restart it to try LLDP discovery."
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fi
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# 4) passive capture for STP/LLDP (tcpdump) - captures broadcast control frames
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if $HAS_TCPDUMP; then
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run_header "Passive capture: look for STP BPDUs and LLDP frames (tcpdump, 6s capture)"
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echo "Capturing for 6 seconds on $IFACE for STP (01:80:c2:00:00:00) and LLDP (0x88cc)"
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TMPPCAP=$(mktemp /tmp/detect_bridge_pcap.XXXX.pcap)
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sudo timeout 6 tcpdump -i "$IFACE" -s 128 -w "$TMPPCAP" "ether dst 01:80:c2:00:00:00 or ether proto 0x88cc or ether multicast" >/dev/null 2>&1 || true
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if [ -s "$TMPPCAP" ]; then
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echo "Captured packets into $TMPPCAP. Decoding summary (tcpdump -r):"
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sudo tcpdump -n -r "$TMPPCAP" -e | sed -n '1,50p' || true
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# search for STP and LLDP keywords
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if sudo tcpdump -n -r "$TMPPCAP" -e | grep -i "stp\|bpdu" >/dev/null 2>&1; then
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echo "-> STP/BPDU frames observed. Very likely a bridge/switch present (could be Linux bridge running STP)."
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fi
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if sudo tcpdump -n -r "$TMPPCAP" -e | grep -i "LLDP" >/dev/null 2>&1; then
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echo "-> LLDP frames observed. This indicates a neighbor device is advertising (switch/bridge)."
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fi
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else
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echo "No control frames captured in 6s capture. That does NOT prove absence of a switch (some devices do not emit LLDP/STP)."
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fi
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rm -f "$TMPPCAP"
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else
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run_header "Passive capture: tcpdump not available"
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echo "tcpdump missing. Install tcpdump and re-run to capture control frames (STP/LLDP)."
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fi
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# 5) ethtool PHY/link partner info
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if $HAS_ETHTOOL; then
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run_header "ethtool: link/partner info"
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echo "(showing ethtool output for $IFACE)"
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sudo ethtool "$IFACE" || true
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echo
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echo "ethtool -a (autoneg/advertised/partner info) if supported:"
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sudo ethtool -a "$IFACE" 2>/dev/null || true
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echo
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echo "ethtool -S (driver stats) if supported:"
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sudo ethtool -S "$IFACE" 2>/dev/null || true
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echo
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echo "Notes: Some drivers expose PHY partner info; presence of a 'PHY' or 'link partner advertised' entry may hint at a switch PHY vs peer NIC."
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else
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run_header "ethtool not available"
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echo "Install ethtool for PHY diagnostics (apt install ethtool)."
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fi
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# 6) ARP / neighbor and MAC lookup
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run_header "ARP table and MAC OUI"
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ip neigh show to "$TARGET_IP" | sed -n '1,50p' || true
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arp_mac=$(ip neigh show to "$TARGET_IP" | awk '{print $5; exit}' || true)
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if [ -n "$arp_mac" ]; then
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echo "Observed MAC for $TARGET_IP: $arp_mac"
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echo "OUI (first 3 octets): $(echo "$arp_mac" | awk -F: '{print toupper($1 $2 $3)}' | sed 's/\(..\)/\1:/g;s/:$//')"
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else
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echo "No ARP entry yet. Try 'arping' or ping to populate ARP."
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fi
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# 7) arping test (if available) - see reply times, flooding behavior
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if $HAS_ARPING; then
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run_header "arping: 5 probes to target (shows ARP replies and timing)"
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echo "(arping may require sudo)"
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sudo timeout 6 arping -c 5 -I "$IFACE" "$TARGET_IP" || true
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else
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run_header "arping: not available"
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echo "Install arping to run ARP-level timing tests (apt install arping)."
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fi
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# 8) ping micro-latency test
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run_header "ping micro-latency test: 100 pings, 10ms interval (if allowed)"
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echo "(This measures latency distribution; software bridge often adds slightly higher microsecond latency.)"
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ping_count=100
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if ping -c 1 "$TARGET_IP" >/dev/null 2>&1; then
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ping -c "$ping_count" -i 0.01 "$TARGET_IP" | tail -n 5
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# compute stats quickly
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stats=$(ping -c "$ping_count" -i 0.01 -q "$TARGET_IP" 2>/dev/null | tail -n1 || true)
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echo "Ping summary: $stats"
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else
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echo "Target is not responding to ICMP, skipping ping test."
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fi
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# 9) traceroute (may help if some IP hops exist)
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if $HAS_TRACEROUTE; then
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run_header "traceroute (ICMP) to target (may not be useful for L2) -- 5 probes"
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traceroute -n -w 1 -q 1 "$TARGET_IP" || true
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else
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run_header "traceroute not available"
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fi
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# 10) passive multicast sniff for other control frames (LLDP multicast 01:80:c2:00:00:0e etc)
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if $HAS_TCPDUMP; then
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run_header "Passive: sniff for LLDP multicast (01:80:c2:00:00:0e) and other bridge groups"
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TMPLOG=$(mktemp /tmp/detect_bridge_log.XXXX.txt)
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sudo timeout 4 tcpdump -i "$IFACE" -s 160 -l -n 'ether multicast' 2>/dev/null | sed -n '1,200p' >"$TMPLOG" || true
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if [ -s "$TMPLOG" ]; then
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echo "Multicast control frames captured (sample):"
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sed -n '1,50p' "$TMPLOG"
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if grep -i "LLDP" "$TMPLOG" >/dev/null 2>&1; then
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echo "-> LLDP present."
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fi
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if grep -i "STP\|BPDU" "$TMPLOG" >/dev/null 2>&1; then
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echo "-> STP/BPDU present."
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fi
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else
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echo "No multicast control frames in short 4s sniff."
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fi
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rm -f "$TMPLOG"
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fi
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# 11) Attempt to infer switch by MAC learning / flood test (non-destructive)
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# Method: send broadcast pings (ARP floods) and observe if any change in behavior
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run_header "Broadcast/ARP flood test (gentle): send 3 ARP probes quickly and observe any flooding/delays"
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if $HAS_ARPING; then
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echo "Sending 3 arping requests spaced tightly to observe behavior..."
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sudo timeout 4 arping -c 3 -I "$IFACE" "$TARGET_IP" >/dev/null 2>&1 || true
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echo "Check dmesg or bridge forwarding table on the local machine (if you manage it) for MAC learning events."
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else
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echo "arping not available -> skipping."
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fi
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# 12) Optional: MAC-spoof learning probe (disabled by default)
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if $MAC_SPOOF = true; then
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echo
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echo "***** MAC SPOOF TEST ENABLED *****"
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echo "This will temporarily change the MAC of $IFACE to a random value and send pings to see whether traffic is forwarded/learned by a bridge."
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echo "If you run this, you MUST ensure you can restore connectivity (script attempts to restore original MAC)."
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read -p "Continue with MAC spoof test? (y/N) " yn
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if [[ "$yn" =~ ^[Yy]$ ]]; then
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orig_mac=$(cat /sys/class/net/"$IFACE"/address)
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rand_mac=$(printf '02:%02x:%02x:%02x:%02x:%02x\n' $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256)))
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echo "Original MAC: $orig_mac"
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echo "Changing $IFACE to $rand_mac"
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sudo ip link set dev "$IFACE" down
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sudo ip link set dev "$IFACE" address "$rand_mac"
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sudo ip link set dev "$IFACE" up
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echo "Sending 5 pings to $TARGET_IP..."
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ping -c 5 "$TARGET_IP" || true
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echo "Restoring original MAC"
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sudo ip link set dev "$IFACE" down
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sudo ip link set dev "$IFACE" address "$orig_mac"
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sudo ip link set dev "$IFACE" up
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echo "MAC restored to $orig_mac"
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else
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echo "Skipping MAC spoof test."
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fi
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else
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echo
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echo "(MAC spoof test disabled. To enable, re-run with --mac-spoof and be prepared for temporary link disruption.)"
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fi
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# 13) Synthesize findings and give a confidence score
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run_header "Synthesis of observations and confidence"
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score=0
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notes=()
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# If we saw STP/BPDU -> strong evidence
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if $HAS_TCPDUMP && sudo tcpdump -n -c 1 -i "$IFACE" 'ether dst 01:80:c2:00:00:00' >/dev/null 2>&1; then
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score=$((score+40))
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notes+=("STP/BPDU frames were observed -> very likely a bridge/switch (possibly Linux bridge running STP).")
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fi
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# LLDP observed
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if $HAS_TCPDUMP && sudo tcpdump -n -c 1 -i "$IFACE" 'ether proto 0x88cc' >/dev/null 2>&1; then
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score=$((score+40))
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notes+=("LLDP frames observed -> neighbor device is advertising (switch/bridge).")
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elif $HAS_LLDPC; then
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# try lldpctl quick check
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if sudo lldpctl "$IFACE" 2>/dev/null | grep -q .; then
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score=$((score+40))
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notes+=("lldpctl shows LLDP neighbor on $IFACE -> neighbor device found (likely bridge/switch).")
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fi
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fi
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# ethtool hints: if ethtool prints "Link detected: yes" but partner info ambiguous; check for PHY entries
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if $HAS_ETHTOOL; then
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if sudo ethtool "$IFACE" 2>/dev/null | grep -qi "Link detected: yes"; then
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# if driver exposes "Link partner" lines, count it as small hint
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if sudo ethtool "$IFACE" 2>/dev/null | grep -i "Link partner\|PHY" >/dev/null 2>&1; then
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score=$((score+5))
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notes+=("ethtool shows PHY/Link-partner info -> small hint the partner may be a switch PHY.")
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fi
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fi
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fi
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# ping/arp timings: if average ping latency > 0.2ms add small weight (depends on environment)
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if ping -c 10 -i 0.01 -q "$TARGET_IP" >/dev/null 2>&1; then
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avg_ms=$(ping -c 10 -i 0.01 -q "$TARGET_IP" 2>/dev/null | tail -n1 | awk -F'/' '{print $5}')
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# if avg above threshold (0.2ms)
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avg_ms_f=$(printf "%.3f" "$avg_ms")
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avg_us=$(awk "BEGIN {print $avg_ms_f*1000}")
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if (( $(echo "$avg_us > 200" | bc -l) )); then
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score=$((score+5))
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notes+=("Ping avg ${avg_ms_f} ms (≈ ${avg_us%.*} µs) — slightly higher than direct NIC-NIC; could indicate software bridging, but not conclusive.")
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fi
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fi
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# ARP behavior: if ARP shows an intermediate device (rare), small weight
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if [ -n "$arp_mac" ]; then
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# if arp_mac OUI seems vendor-like? we can't lookup vendor offline, but if OUI ends with 00:00:00 unlikely
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score=$((score+2))
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notes+=("ARP resolved target's MAC (${arp_mac}). (By itself this is expected and not a proof for/against a bridge.)")
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fi
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# ip link master: if interface is enslaved locally -> local bridge
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if [ -n "$master" ]; then
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score=$((score+30))
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notes+=("Interface master indicates this host is attached to a local bridge ($master) — local bridge present.")
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fi
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# TTL/hops/traceroute: generally not useful, but check if traceroute shows multiple hops
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if $HAS_TRACEROUTE; then
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hops=$(traceroute -n -q 1 -w 1 -m 3 "$TARGET_IP" 2>/dev/null | awk 'NR>1 {print $2}' | wc -l)
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if [ "$hops" -gt 1 ]; then
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score=$((score+2))
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notes+=("traceroute showed more than 1 hop (rare for pure L2) — inspect carefully.")
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fi
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fi
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# Cap score 0-100
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if [ "$score" -gt 100 ]; then score=100; fi
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echo "Score: $score / 100"
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echo
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echo "Notes:"
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for n in "${notes[@]}"; do
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echo " - $n"
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done
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echo
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if [ "$score" -ge 70 ]; then
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echo "Conclusion: HIGH confidence there is a switch/bridge between the hosts."
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elif [ "$score" -ge 35 ]; then
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echo "Conclusion: MEDIUM confidence of a switch/bridge between hosts. Some signals found but not definitive."
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else
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echo "Conclusion: LOW confidence. No strong evidence found; switch could still be present but silent (no LLDP/STP), or path may be direct."
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fi
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echo
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echo "Recommendations:"
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echo " - If you control the intermediate device, check 'brctl show' or 'bridge link' on that host."
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echo " - Enable lldpd on the bridge (sudo apt install lldpd) and use lldpctl on both ends."
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echo " - If tcpdump showed STP/BPDU or LLDP, that's the most direct evidence."
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echo
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echo "Done." |