mxsnoop.sh

#!/bin/bash

#
#  +--------------+   (!)   +----------------------+        +---****
#  |              |         |        br01          |        |
#  | THE SUSPECT  O]===X===[O   SCHNUEFFELSTUECK   O]======[O  WIS-NET
#  |              |         |INLET           OUTLET|        |
#  +--------------+         +----------------------+        +---****
#                                        (MX_NETDEV)

#  Basics: https://wiki.archlinux.org/title/Network_bridge

# GATEWAY=10.0.3.1
# BROADCAST=10.0.3.255
# NETMASK=255.255.255.0
# NIDL=24

GATEWAY=141.14.16.128
BROADCAST=141.14.31.255
NETMASK=255.255.240.0
NIDL=20

INLET=${INLET:-}
OUTLET=${OUTLET:-}
BRIDGE=br01

TRANSPARENT=${TRANSPARENT:-}
STP=${STP:-}

function die() { echo "$1"; exit 1; }

type ip > /dev/null || \
  die 'Error: Tools not available, check for ip command.'

MXHOSTCONF=${MXHOSTCONF:-/etc/local/mxhost.conf}
source $MXHOSTCONF || die "# Error: No 'mxhost.conf' ?"
test -n "$MX_IPADDR" || die '# Error: MX_IPADDR missing.'

if [ -z "$OUTLET" ]; then
  test -n "$MX_NETDEV" || die '# Error: MX_NETDEV missing?'
  test -e /sys/class/net/$MX_NETDEV || die "# Error: $MX_NETDEV missing."
  OUTLET=$MX_NETDEV
fi


# inlet was present at boot time -> netXY, or plugged later -> Search for ethX
if [ -z "$INLET" ]; then # find the (sole) inlet
  for D in net{00..09} eth{0..9}; do
    test -e /sys/class/net/$D || continue
    test $D = $OUTLET && continue
    test -n "$INLET" && \
      die 'Error: Too many network devices (netXY) present, use INLET=dev (OUTLET=dev ?).'
    INLET=$D
  done
fi

test -z "$INLET" && die '# Error: no second network device found.'

echo "# Note: about to setup/destroy $BRIDGE between $INLET (INLET) and $OUTLET (OUTLET), IP: $MX_IPADDR"

cmd="$1"

case "$cmd" in

  start)

    if [ -z "$STP" ]; then
      ip link add dev $BRIDGE type bridge
    else
      ip link add dev $BRIDGE type bridge stp_state 1
    fi

    ip address flush dev $INLET
    ip address flush dev $OUTLET

    ip link set $INLET master $BRIDGE
    ip link set $OUTLET master $BRIDGE

    if [ -z "$TRANSPARENT" ] ; then
      ip addr add $MX_IPADDR/$NIDL broadcast $BROADCAST dev $BRIDGE
      ip link set up dev $BRIDGE
      ip route add default via $GATEWAY dev $BRIDGE
    fi

    ip link set dev $INLET up
    ip link set dev $OUTLET up

    ;;

  stop)

    ip link set $INLET nomaster
    ip link set $OUTLET nomaster
    ip link delete $BRIDGE type bridge

    ip addr add $MX_IPADDR/$NIDL broadcast $BROADCAST dev $OUTLET
    ip link set dev $OUTLET up
    ip route add default via $GATEWAY

    ;;

  restart)

    $0 stop
    sleep 1
    $0 start
    ;;

  *)

    echo "#   usage:     [INLET=dev] [OUTLET=dev] $0 [start|stop|restart]"
    echo "# options:     TRANSPARENT=1 doesn't bind IP on the bridge"
    echo "#              STP=1 enables Spanning Tree"
    ;;

esac