W-Floyd · February 17, 2025 15:57 · W-Floyd · Feb 11, 2025
diff --git a/mtu-finder.sh b/mtu-finder.sh
 #!/bin/bash
 PS4='\033[0;33m+(${BASH_SOURCE}:${LINENO}):\033[0m ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'
 set -e
 # set -xE -o functrace

 # Internal parameters

 __mtu_largest_success=0
 __mtu_smallest_fail=0
 __ping_mtu_byte_offset=-24
 __mode=""

 # Defaults
 __mtu=""
 __mtu_growth_factor="2"
 __timeout="1.0"
 __default_mode="ping"
 __vpn_curl_address=""
 __network_interface=""
 __ping_address="google.com"
 __max_retries='2'

 __help_string="${0} - A script to find an appropriate MTU size by experimentation

 -h | --help                   - Program usage

 -s | --mtu-start <n>          - Starting MTU for testing (integer, default derived from interface)
 -g | --mtu-growth-factor <n>  - MTU growth factor (integer, default: '${__mtu_growth_factor}')
 -t | --timeout <t>            - Operation timeout (float seconds, default: '${__timeout}')
 -i | --interface <interface>  - Network interface to use (default: default derived from mode)
 -r | --retries <n>            - Maximum number of retries on inconsistency (default: '${__max_retries}')
 -m | --mode vpn|ping          - Mode to test with (default: '${__default_mode}')
                                If unset, will use the default, or infer it from the mode options used
                                   vpn - Modifies live VPN MTU and tests with curl
                                  ping - Tests maximum ping size to find MTU

 VPN Options:
 -c | --curl-address <address> - Address to test using curl (default: '${__vpn_curl_address}')

 Ping Options:
 -p | --ping-address <address> - Address to test using ping (default: '${__ping_address}')"

 # Functions
 function __set_mode() {
    if (! [[ -z "${__mode}" ]]) || [[ -z "${1}" ]]; then
        echo "Please specify only one operating mode"
        return 1
    else
        __mode="${1}"
    fi
 }

 function __require_mode() {
    if [[ -z "${__mode}" ]]; then
        __set_mode "${1}" || return 1
    fi
    if [[ "${__mode}" != "${1}" ]]; then
        echo "Option '${2}' must be used with operating mode ${1}"
        return 1
    fi
 }

 function __has() {
    shift
    if [[ "${#}" -lt "${1}" ]]; then
        echo "Not enough arguments provided"
        return 1
    fi
 }

 # Parse Options
 while [[ "${#}" -gt 0 ]]; do
    case "${1}" in
    "-h" | "--help")
        echo "${__help_string}"
        exit
        ;;
    "--mtu-start" | "-s")
        __has 2 ${@} || exit 1
        __mtu="${2}"
        shift 2
        ;;
    "--mtu-growth-factor" | "-g")
        __has 2 ${@} || exit 1
        __mtu_growth_factor="${2}"
        shift 2
        ;;
    "--timeout" | "-t")
        __has 2 ${@} || exit 1
        __timeout="${2}"
        shift 2
        ;;
    "-i" | "--interface")
        __has 2 ${@} || exit 1
        __network_interface="${2}"
        shift 2
        ;;
    "-r" | "--retries")
        __has 2 ${@} || exit 1
        __max_retries="${2}"
        shift 2
        ;;
    "--mode" | "-m")
        __has 2 ${@} || exit 1
        __set_mode "${2}" || exit 1
        shift 2
        ;;
    "-c" | "--curl-address")
        __has 2 ${@} || exit 1
        __require_mode 'vpn' "${1}" || exit 1
        __vpn_curl_address="${2}"
        shift 2
        ;;
    "-p" | "--ping-address")
        __has 2 ${@} || exit 1
        __require_mode 'ping' "${1}" || exit 1
        __ping_address="${2}"
        shift 2
        ;;

    *)
        echo "Unknown option ${1}"
        exit 1
        ;;
    esac
 done

 if [[ -z "${__mode}" ]]; then
    __mode="${__default_mode}"
 fi

 function __test_mtu_ping() {
    ping -4 "${__ping_address}" -c 1 -W "${__timeout}" -s "$((${1} - ${__ping_mtu_byte_offset}))" -I "${__network_interface}" -q &>/dev/null || return 1
 }

 function __test_mtu_vpn() {
    sudo ip link set dev "${__network_interface}" mtu "${1}"
    sleep 0.2 # This can help prevent random failures
    curl \
        "${__vpn_curl_address}" \
        -s \
        -o /dev/null \
        -m "${__timeout}" &&
        return 0 ||
        return 1
 }

 function __test() {
    __test_mtu="${__mtu}"
    if ! [ -z "${1}" ]; then
        __test_mtu="${1}"
    fi
    __test_retry_count='0'
    while true; do
        case "${__mode}" in
        "vpn")
            __test_mtu_vpn "${__test_mtu}" && return 0 || __test_retry_count="$((${__test_retry_count} + 1))"
            ;;
        "ping")
            __test_mtu_ping "${__test_mtu}" && return 0 || __test_retry_count="$((${__test_retry_count} + 1))"
            ;;
        esac
        if [[ "${__test_retry_count}" -gt 2 ]]; then
            return 1
        fi
    done
 }

 case "${__mode}" in
 "vpn")
    if [[ -z "${__network_interface}" ]]; then
        __network_interface='tun0'
    fi
    ip addr show "${__network_interface}" &>/dev/null ||
        (
            echo "Interface '${__network_interface}' does not exist"
            exit 1
        )
    if [[ -z "${__vpn_curl_address}" ]]; then
        echo 'VPN curl address empty'
        exit 1
    fi
    echo 'Need root access, testing...'
    sudo echo 'Done'
    ;;
 "ping")
    if [[ -z "${__network_interface}" ]]; then
        __ip=$(getent ahosts "${__ping_address}" | awk '{print $1; exit}')
        __network_interface="$(ip route get "${__ip}" | grep -Po '(?<=(dev ))(\S+)')"
    fi
    echo '⚠️ WARNING: Ping may result in incorrect detected MTU depending on what host is specified'
    echo "Pinging: ${__ping_address}"
    ;;
 *)
    echo "Unknown mode '${__mode}'"
    exit 1
    ;;
 esac

 __mtu_detected='0'

 echo -n "Detecting mtu from '${__network_interface}'... "
 __mtu_detected="$(ip link show "${__network_interface}" | grep -Eo 'mtu [0-9]+' | sed -e 's/.* //')"
 echo "${__mtu_detected}"
 if [[ -z "${__mtu}" ]]; then
    __mtu="${__mtu_detected}"
 fi

 __retry_count=0

 while true; do

    if [[ "${__retry_count}" -gt "${__max_retries}" ]]; then
        echo "Exceeded maximum retries of '${__max_retries}', giving up"
        exit 1
    fi

    if [[ "${__last_mtu}" == "${__mtu}" ]]; then
        echo "Repeated MTU"
        exit 1
    fi

    __last_mtu="${__mtu}"

    echo -n "Testing MTU: ${__mtu}... "
    if __test "${__mtu}"; then
        echo "✔️"
        __mtu_largest_success="${__mtu}"
        if [[ "${__mtu_smallest_fail}" == 0 ]]; then
            if [[ "${__mtu}" == "${__mtu_detected}" ]]; then
                __mtu="$((${__mtu} + 1))"
            else
                __mtu="$((${__mtu_largest_success} * ${__mtu_growth_factor}))"
            fi
            continue
        fi
    else
        echo "❌"
        __mtu_smallest_fail="${__mtu}"
        if [[ "${__mode}" == 'ping' ]] && ! [[ "${__mtu}" -gt 28 ]]; then
            echo "Ping to '${__ping_address}' failed at <=28 bytes, please change interfaces or specify a host that is pingable"
            exit 1
        fi
    fi
    __mtu="$((${__mtu_largest_success} + (${__mtu_smallest_fail} - ${__mtu_largest_success}) / 2))"
    if [[ "$((${__mtu_smallest_fail} - ${__mtu_largest_success}))" == 1 ]]; then
        echo -n "Confirming results... "
        if (! __test "${__mtu_smallest_fail}") && (__test "${__mtu_largest_success}"); then
            echo "✔️"
            echo "Largest working MTU: ${__mtu}"
            echo
            break
        else
            echo "❌"
            echo "Inconsistent results, retesting!"

            echo 'Resetting upper bound'
            __mtu_smallest_fail=0
            __last_mtu=0

            __retry_count="$((${__retry_count} + 1))"

        fi
    fi
 done

 if [[ "${__mtu_detected}" == "${__mtu}" ]]; then
    echo -e "Interface '${__network_interface}' is already using the maximum MTU: ${__mtu}"
 else
    echo -e "Add the following to your .ovpn file:\npull-filter ignore \"tun-mtu\"\ntun-mtu ${__mtu}"
 fi

 exit
	#!/bin/bash
	PS4='\033[0;33m+(${BASH_SOURCE}:${LINENO}):\033[0m ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'
	set -e
	# set -xE -o functrace

	# Internal parameters

	__mtu_largest_success=0
	__mtu_smallest_fail=0
	__ping_mtu_byte_offset=-24
	__mode=""

	# Defaults
	__mtu=""
	__mtu_growth_factor="2"
	__timeout="1.0"
	__default_mode="ping"
	__vpn_curl_address=""
	__network_interface=""
	__ping_address="google.com"
	__max_retries='2'

	__help_string="${0} - A script to find an appropriate MTU size by experimentation

	-h \| --help - Program usage

	-s \| --mtu-start <n> - Starting MTU for testing (integer, default derived from interface)
	-g \| --mtu-growth-factor <n> - MTU growth factor (integer, default: '${__mtu_growth_factor}')
	-t \| --timeout <t> - Operation timeout (float seconds, default: '${__timeout}')
	-i \| --interface <interface> - Network interface to use (default: default derived from mode)
	-r \| --retries <n> - Maximum number of retries on inconsistency (default: '${__max_retries}')
	-m \| --mode vpn\|ping - Mode to test with (default: '${__default_mode}')
	If unset, will use the default, or infer it from the mode options used
	vpn - Modifies live VPN MTU and tests with curl
	ping - Tests maximum ping size to find MTU

	VPN Options:
	-c \| --curl-address <address> - Address to test using curl (default: '${__vpn_curl_address}')

	Ping Options:
	-p \| --ping-address <address> - Address to test using ping (default: '${__ping_address}')"

	# Functions
	function __set_mode() {
	if (! [[ -z "${__mode}" ]]) \|\| [[ -z "${1}" ]]; then
	echo "Please specify only one operating mode"
	return 1
	else
	__mode="${1}"
	fi
	}

	function __require_mode() {
	if [[ -z "${__mode}" ]]; then
	__set_mode "${1}" \|\| return 1
	fi
	if [[ "${__mode}" != "${1}" ]]; then
	echo "Option '${2}' must be used with operating mode ${1}"
	return 1
	fi
	}

	function __has() {
	shift
	if [[ "${#}" -lt "${1}" ]]; then
	echo "Not enough arguments provided"
	return 1
	fi
	}

	# Parse Options
	while [[ "${#}" -gt 0 ]]; do
	case "${1}" in
	"-h" \| "--help")
	echo "${__help_string}"
	exit
	;;
	"--mtu-start" \| "-s")
	__has 2 ${@} \|\| exit 1
	__mtu="${2}"
	shift 2
	;;
	"--mtu-growth-factor" \| "-g")
	__has 2 ${@} \|\| exit 1
	__mtu_growth_factor="${2}"
	shift 2
	;;
	"--timeout" \| "-t")
	__has 2 ${@} \|\| exit 1
	__timeout="${2}"
	shift 2
	;;
	"-i" \| "--interface")
	__has 2 ${@} \|\| exit 1
	__network_interface="${2}"
	shift 2
	;;
	"-r" \| "--retries")
	__has 2 ${@} \|\| exit 1
	__max_retries="${2}"
	shift 2
	;;
	"--mode" \| "-m")
	__has 2 ${@} \|\| exit 1
	__set_mode "${2}" \|\| exit 1
	shift 2
	;;
	"-c" \| "--curl-address")
	__has 2 ${@} \|\| exit 1
	__require_mode 'vpn' "${1}" \|\| exit 1
	__vpn_curl_address="${2}"
	shift 2
	;;
	"-p" \| "--ping-address")
	__has 2 ${@} \|\| exit 1
	__require_mode 'ping' "${1}" \|\| exit 1
	__ping_address="${2}"
	shift 2
	;;

	*)
	echo "Unknown option ${1}"
	exit 1
	;;
	esac
	done

	if [[ -z "${__mode}" ]]; then
	__mode="${__default_mode}"
	fi

	function __test_mtu_ping() {
	ping -4 "${__ping_address}" -c 1 -W "${__timeout}" -s "$((${1} - ${__ping_mtu_byte_offset}))" -I "${__network_interface}" -q &>/dev/null \|\| return 1
	}

	function __test_mtu_vpn() {
	sudo ip link set dev "${__network_interface}" mtu "${1}"
	sleep 0.2 # This can help prevent random failures
	curl \
	"${__vpn_curl_address}" \
	-s \
	-o /dev/null \
	-m "${__timeout}" &&
	return 0 \|\|
	return 1
	}

	function __test() {
	__test_mtu="${__mtu}"
	if ! [ -z "${1}" ]; then
	__test_mtu="${1}"
	fi
	__test_retry_count='0'
	while true; do
	case "${__mode}" in
	"vpn")
	__test_mtu_vpn "${__test_mtu}" && return 0 \|\| __test_retry_count="$((${__test_retry_count} + 1))"
	;;
	"ping")
	__test_mtu_ping "${__test_mtu}" && return 0 \|\| __test_retry_count="$((${__test_retry_count} + 1))"
	;;
	esac
	if [[ "${__test_retry_count}" -gt 2 ]]; then
	return 1
	fi
	done
	}

	case "${__mode}" in
	"vpn")
	if [[ -z "${__network_interface}" ]]; then
	__network_interface='tun0'
	fi
	ip addr show "${__network_interface}" &>/dev/null \|\|
	(
	echo "Interface '${__network_interface}' does not exist"
	exit 1
	)
	if [[ -z "${__vpn_curl_address}" ]]; then
	echo 'VPN curl address empty'
	exit 1
	fi
	echo 'Need root access, testing...'
	sudo echo 'Done'
	;;
	"ping")
	if [[ -z "${__network_interface}" ]]; then
	__ip=$(getent ahosts "${__ping_address}" \| awk '{print $1; exit}')
	__network_interface="$(ip route get "${__ip}" \| grep -Po '(?<=(dev ))(\S+)')"
	fi
	echo '⚠️ WARNING: Ping may result in incorrect detected MTU depending on what host is specified'
	echo "Pinging: ${__ping_address}"
	;;
	*)
	echo "Unknown mode '${__mode}'"
	exit 1
	;;
	esac

	__mtu_detected='0'

	echo -n "Detecting mtu from '${__network_interface}'... "
	__mtu_detected="$(ip link show "${__network_interface}" \| grep -Eo 'mtu [0-9]+' \| sed -e 's/.* //')"
	echo "${__mtu_detected}"
	if [[ -z "${__mtu}" ]]; then
	__mtu="${__mtu_detected}"
	fi

	__retry_count=0

	while true; do

	if [[ "${__retry_count}" -gt "${__max_retries}" ]]; then
	echo "Exceeded maximum retries of '${__max_retries}', giving up"
	exit 1
	fi

	if [[ "${__last_mtu}" == "${__mtu}" ]]; then
	echo "Repeated MTU"
	exit 1
	fi

	__last_mtu="${__mtu}"

	echo -n "Testing MTU: ${__mtu}... "
	if __test "${__mtu}"; then
	echo "✔️"
	__mtu_largest_success="${__mtu}"
	if [[ "${__mtu_smallest_fail}" == 0 ]]; then
	if [[ "${__mtu}" == "${__mtu_detected}" ]]; then
	__mtu="$((${__mtu} + 1))"
	else
	__mtu="$((${__mtu_largest_success} * ${__mtu_growth_factor}))"
	fi
	continue
	fi
	else
	echo "❌"
	__mtu_smallest_fail="${__mtu}"
	if [[ "${__mode}" == 'ping' ]] && ! [[ "${__mtu}" -gt 28 ]]; then
	echo "Ping to '${__ping_address}' failed at <=28 bytes, please change interfaces or specify a host that is pingable"
	exit 1
	fi
	fi
	__mtu="$((${__mtu_largest_success} + (${__mtu_smallest_fail} - ${__mtu_largest_success}) / 2))"
	if [[ "$((${__mtu_smallest_fail} - ${__mtu_largest_success}))" == 1 ]]; then
	echo -n "Confirming results... "
	if (! __test "${__mtu_smallest_fail}") && (__test "${__mtu_largest_success}"); then
	echo "✔️"
	echo "Largest working MTU: ${__mtu}"
	echo
	break
	else
	echo "❌"
	echo "Inconsistent results, retesting!"

	echo 'Resetting upper bound'
	__mtu_smallest_fail=0
	__last_mtu=0

	__retry_count="$((${__retry_count} + 1))"

	fi
	fi
	done

	if [[ "${__mtu_detected}" == "${__mtu}" ]]; then
	echo -e "Interface '${__network_interface}' is already using the maximum MTU: ${__mtu}"
	else
	echo -e "Add the following to your .ovpn file:\npull-filter ignore \"tun-mtu\"\ntun-mtu ${__mtu}"
	fi

	exit