setup-iproute-modem-policies.sh

#!/bin/bash

declare -A MODEMS

MODEMS=(["alpha"]="192.168.12.100" ["beta"]="192.168.10.100" ["delta"]="192.168.9.100" ["omega"]="192.168.11.100")

for modem_name in "${!MODEMS[@]}"; do
  ip_address="${MODEMS[$modem_name]}"
  IFACE=$(ip -o addr show | grep -w ${ip_address} | awk '{print $2}')
  if [ -z "$IFACE" ]; then continue; fi

  GATEWAY=$(ip route show default dev $IFACE | awk '{print $3}')

  echo "$modem_name ($ip_address) gw: $GATEWAY, if: $IFACE"

  rules=$(ip rule list | grep "lookup $modem_name" | awk '{print substr($1, 1, length($1)-1)}')
  for priority in $rules; do
    ip rule del pref $priority table $modem_name
  done

  ip rule add from $ip_address table $modem_name
  ip route flush table $modem_name
  ip route add default via $GATEWAY dev $IFACE table $modem_name
done

ip route flush cache