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#!/bin/bash
unwind() {
ip route del "$1/32" 2>/dev/null
exit
}
short_route() {
ip route | sed -n "s/$1 \\(.* dev [^ ]\\+\\).*/\\1/p" | head -n 1
}
resolve_ip() {
local filter='/^[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}$/{p;q;}'
[[ $(sed -n "$filter" <<<"$1") == "$1" ]] && echo "$1" ||
host -t a "$1" | cut -d ' ' -f 4 | sed -n "$filter"
}
set_route() {
local default_route="$(short_route default)"
[[ -n $default_route ]] || { echo "[-] Could not determine default route"; return; }
echo "[+] Adding route for $1 to be $default_route"
ip route del "$1/32" 2>/dev/null
ip route add "$1/32" $default_route
}
check_loop() {
local ip="$(resolve_ip "$1")"
[[ -n $ip ]] || { echo "[-] Could not determine IP of '$1'" && return 1; }
echo "[+] Making sure $ip goes over the default (non-0/1,128/1) route"
set_route "$ip"
trap unwind INT TERM EXIT
while read -r; do
[[ $(short_route "$ip") != "$(short_route default)" ]] && set_route "$ip"
done < <(exec ip monitor route)
}
[[ $# -ne 1 ]] && { echo "Usage: $0 IP|HOST" >&2; exit 1; }
[[ $UID -ne 0 ]] && exec sudo "$(readlink -f "$0")" "$@"
check_loop "$1"
exit $?
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