preventing dropped wifi connections [SOLVED]

[GNUser]

PROBLEM:
I was experiencing unexplained dropped wifi connections when using my Pure64 10.1 laptop at work. The place where I work has a complex network that's open (no password) and has thousands of clients connected at the same time. My guess is that it uses IPv6 to some extent, but I can't say for sure. My laptop has an Atheros wireless card (AR928X per lshw) and, per iwconfig and cat /sys/module/ath9k/parameters/ps_enable, "power management" is off.

The only output I could find at time of dropped connections were single lines in output of dmesg, either this:

Code: [Select]

wlan0: deauthenticating from <mac address> by local choice (Reason: 1=UNSPECIFIED)
or this: 

Code: [Select]

wlan0: deauthenticating from <mac address> by local choice (Reason: 3=DEAUTH_LEAVING)

Not very helpful.

My setup when I was experiencing the dropped connections: IPv6 disabled (ipv6-4.16.10-tinycore64.tcz was not loaded), iwconfig to connect to open networks, udhcpc as DCHP client. This was the key part of my autowifi script (which runs with root privileges):

Code: [Select]

ssid=WorkplaceOpen
iface=wlan0

iwconfig wlan0 essid "$ssid" &
sleep 3
udhcpc -i $iface

SOLUTION:
Since I wasn't finding any specific clues as to the nature of the problem, I thought I'd throw everything but the kitchen sink at it: IPv6 enabled, wpa_supplicant to connect to open networks as well as encrypted ones, dhclient as DHCP client.

To support the new approach, I needed to install two additional extensions:

Code: [Select]

tce-load -wi ipv6-4.19.10-tinycore64 dhcp

dhclient is quite fussy compared to udhcpc: It needs a) a configuration file, b) a script to run after it does some initial work, and c) an empty directory in which to save details of current leases.

a) Here is the configuration file, /etc/dhcp/dhclient.conf, which I cobbled together by cheating and seeing what NetworkManager uses when running in Devuan:

Code: [Select]

option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;
option ms-classless-static-routes code 249 = array of unsigned integer 8;
option wpad code 252 = string;

send host-name = gethostname();

request subnet-mask, broadcast-address, time-offset, routers,
domain-search, domain-name-servers, host-name,
dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn, dhcp6.sntp-servers,
netbios-name-servers, netbios-scope, interface-mtu,
rfc3442-classless-static-routes, ntp-servers, ms-classless-static-routes, wpad;
b) Here is /sbin/dhclient-script, which I copied from Devuan:

Code: [Select]

#!/bin/sh

# dhclient-script for Linux. Dan Halbert, March, 1997.
# Updated for Linux 2.[12] by Brian J. Murrell, January 1999.
# Modified for Debian.  Matt Zimmerman and Eloy Paris, December 2003
# Modified to remove useless tests for antiquated kernel versions that
# this doesn't even work with anyway, and introduces a dependency on /usr
# being mounted, which causes cosmetic errors on hosts that NFS mount /usr
# Andrew Pollock, February 2005
# Modified to work on point-to-point links. Andrew Pollock, June 2005
# Modified to support passing the parameters called with to the hooks. Andrew Pollock, November 2005
# Modified to work on Busybox, whose chown and chmod applets do not have the '--reference' flag. GNUser, November 2019

# The alias handling in here probably still sucks. -mdz

# wait for given file to be writable
wait_for_rw() {
    local file=$1
    # Find out whether we are going to mount / rw
    exec 9>&0 </etc/fstab
    rootmode=rw
    while read dev mnt type opts dump pass junk; do
        [ "$mnt" != / ] && continue
        case "$opts" in
            ro|ro,*|*,ro|*,ro,*)
               rootmode=ro
               ;;
             esac
     done
     exec 0>&9 9>&-

    # Wait for $file to become writable
    if [ "$rootmode" = "rw" ]; then
        while ! { : >> "$file"; } 2>/dev/null; do
            sleep 0.1
        done
    fi
}

# update /etc/resolv.conf based on received values
make_resolv_conf() {
    local new_resolv_conf

    # DHCPv4
    if [ -n "$new_domain_search" ] || [ -n "$new_domain_name" ] ||
       [ -n "$new_domain_name_servers" ]; then
        resolv_conf=$(readlink -f "/etc/resolv.conf" 2>/dev/null) ||
            resolv_conf="/etc/resolv.conf"

        new_resolv_conf="${resolv_conf}.dhclient-new.$$"
        wait_for_rw "$new_resolv_conf"
        rm -f $new_resolv_conf

        if [ -n "$new_domain_name" ]; then
            echo domain ${new_domain_name%% *} >>$new_resolv_conf
        fi

        if [ -n "$new_domain_search" ]; then
            if [ -n "$new_domain_name" ]; then
                domain_in_search_list=""
                for domain in $new_domain_search; do
                    if [ "$domain" = "${new_domain_name}" ] ||
                       [ "$domain" = "${new_domain_name}." ]; then
                        domain_in_search_list="Yes"
                    fi
                done
                if [ -z "$domain_in_search_list" ]; then
                    new_domain_search="$new_domain_name $new_domain_search"
                fi
            fi
            echo "search ${new_domain_search}" >> $new_resolv_conf
        elif [ -n "$new_domain_name" ]; then
            echo "search ${new_domain_name}" >> $new_resolv_conf
        fi

        if [ -n "$new_domain_name_servers" ]; then
            for nameserver in $new_domain_name_servers; do
                echo nameserver $nameserver >>$new_resolv_conf
            done
        else # keep 'old' nameservers
            sed -n /^\w*[Nn][Aa][Mm][Ee][Ss][Ee][Rr][Vv][Ee][Rr]/p $resolv_conf >>$new_resolv_conf
        fi

if [ -f $resolv_conf ]; then
    #chown --reference=$resolv_conf $new_resolv_conf
    chown root:root $new_resolv_conf
    #chmod --reference=$resolv_conf $new_resolv_conf
    chmod 644 $new_resolv_conf
fi
        mv -f $new_resolv_conf $resolv_conf
    # DHCPv6
    elif [ -n "$new_dhcp6_domain_search" ] || [ -n "$new_dhcp6_name_servers" ]; then
        resolv_conf=$(readlink -f "/etc/resolv.conf" 2>/dev/null) ||
            resolv_conf="/etc/resolv.conf"

        new_resolv_conf="${resolv_conf}.dhclient-new.$$"
        wait_for_rw "$new_resolv_conf"
        rm -f $new_resolv_conf

        if [ -n "$new_dhcp6_domain_search" ]; then
            echo "search ${new_dhcp6_domain_search}" >> $new_resolv_conf
        fi

        if [ -n "$new_dhcp6_name_servers" ]; then
            for nameserver in $new_dhcp6_name_servers; do
                # append %interface to link-local-address nameservers
                if [ "${nameserver##fe80::}" != "$nameserver" ] ||
                   [ "${nameserver##FE80::}" != "$nameserver" ]; then
                    nameserver="${nameserver}%${interface}"
                fi
                echo nameserver $nameserver >>$new_resolv_conf
            done
        else # keep 'old' nameservers
            sed -n /^\w*[Nn][Aa][Mm][Ee][Ss][Ee][Rr][Vv][Ee][Rr]/p $resolv_conf >>$new_resolv_conf
        fi

if [ -f $resolv_conf ]; then
            #chown --reference=$resolv_conf $new_resolv_conf
            chown root:root $new_resolv_conf
            #chmod --reference=$resolv_conf $new_resolv_conf
            chmod 644 $new_resolv_conf
fi
        mv -f $new_resolv_conf $resolv_conf
    fi
}

# set host name
set_hostname() {
    if [ -n "$new_host_name" ]; then
        local current_hostname=$(hostname)

        # current host name is empty, '(none)' or 'localhost' or differs from new one from DHCP
        if [ -z "$current_hostname" ] ||
           [ "$current_hostname" = '(none)' ] ||
           [ "$current_hostname" = 'localhost' ] ||
           [ "$current_hostname" = "$old_host_name" ]; then
           if [ "$new_host_name" != "$current_host_name" ]; then
               hostname "$new_host_name"
           fi
        fi
    fi
}

# run given script
run_hook() {
    local script="$1"
    local exit_status=0

    if [ -f $script ]; then
        . $script
        exit_status=$?
    fi

    if [ -n "$exit_status" ] && [ "$exit_status" -ne 0 ]; then
        logger -p daemon.err "$script returned non-zero exit status $exit_status"
    fi

    return $exit_status
}

# run scripts in given directory
run_hookdir() {
    local dir="$1"
    local exit_status=0

    if [ -d "$dir" ]; then
        for script in $(run-parts --list $dir); do
            run_hook $script
            exit_status=$((exit_status|$?))
        done
    fi

    return $exit_status
}

# Must be used on exit.   Invokes the local dhcp client exit hooks, if any.
exit_with_hooks() {
    local exit_status=$1

    # Source the documented exit-hook script, if it exists
    if ! run_hook /etc/dhcp/dhclient-exit-hooks; then
        exit_status=$?
    fi

    # Now run scripts in the Debian-specific directory.
    if ! run_hookdir /etc/dhcp/dhclient-exit-hooks.d; then
        exit_status=$?
    fi

    exit $exit_status
}


# The 576 MTU is only used for X.25 and dialup connections
# where the admin wants low latency.  Such a low MTU can cause
# problems with UDP traffic, among other things.  As such,
# disallow MTUs from 576 and below by default, so that broken
# MTUs are ignored, but higher stuff is allowed (1492, 1500, etc).
if [ -z "$new_interface_mtu" ] || [ "$new_interface_mtu" -le 576 ]; then
    new_interface_mtu=''
fi


# The action starts here

# Invoke the local dhcp client enter hooks, if they exist.
run_hook /etc/dhcp/dhclient-enter-hooks
run_hookdir /etc/dhcp/dhclient-enter-hooks.d

# Execute the operation
case "$reason" in

    ### DHCPv4 Handlers

    MEDIUM|ARPCHECK|ARPSEND)
        # Do nothing
        ;;
    PREINIT)
        # The DHCP client is requesting that an interface be
        # configured as required in order to send packets prior to
        # receiving an actual address. - dhclient-script(8)

        # ensure interface is up
        ip link set dev ${interface} up

        if [ -n "$alias_ip_address" ]; then
            # flush alias IP from interface
            ip -4 addr flush dev ${interface} label ${interface}:0
        fi

        ;;

    BOUND|RENEW|REBIND|REBOOT)
        set_hostname

        if [ -n "$old_ip_address" ] && [ -n "$alias_ip_address" ] &&
           [ "$alias_ip_address" != "$old_ip_address" ]; then
            # alias IP may have changed => flush it
            ip -4 addr flush dev ${interface} label ${interface}:0
        fi

        if [ -n "$old_ip_address" ] &&
           [ "$old_ip_address" != "$new_ip_address" ]; then
            # leased IP has changed => flush it
            ip -4 addr flush dev ${interface} label ${interface}
        fi

        if [ -z "$old_ip_address" ] ||
           [ "$old_ip_address" != "$new_ip_address" ] ||
           [ "$reason" = "BOUND" ] || [ "$reason" = "REBOOT" ]; then
            # new IP has been leased or leased IP changed => set it
            ip -4 addr add ${new_ip_address}${new_subnet_mask:+/$new_subnet_mask} \
                ${new_broadcast_address:+broadcast $new_broadcast_address} \
                dev ${interface} label ${interface}

            if [ -n "$new_interface_mtu" ]; then
                # set MTU
                ip link set dev ${interface} mtu ${new_interface_mtu}
            fi

    # if we have $new_rfc3442_classless_static_routes then we have to
    # ignore $new_routers entirely
    if [ ! "$new_rfc3442_classless_static_routes" ]; then
    # set if_metric if IF_METRIC is set or there's more than one router
    if_metric="$IF_METRIC"
    if [ "${new_routers%% *}" != "${new_routers}" ]; then
if_metric=${if_metric:-1}
    fi

    for router in $new_routers; do
if [ "$new_subnet_mask" = "255.255.255.255" ]; then
    # point-to-point connection => set explicit route
    ip -4 route add ${router} dev $interface >/dev/null 2>&1
fi

# set default route
ip -4 route add default via ${router} dev ${interface} \
    ${if_metric:+metric $if_metric} >/dev/null 2>&1

if [ -n "$if_metric" ]; then
    if_metric=$((if_metric+1))
fi
    done
    fi
        fi

        if [ -n "$alias_ip_address" ] &&
           [ "$new_ip_address" != "$alias_ip_address" ]; then
            # separate alias IP given, which may have changed
            # => flush it, set it & add host route to it
            ip -4 addr flush dev ${interface} label ${interface}:0
            ip -4 addr add ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
                dev ${interface} label ${interface}:0
            ip -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
        fi

        # update /etc/resolv.conf
        make_resolv_conf

        ;;

    EXPIRE|FAIL|RELEASE|STOP)
        if [ -n "$alias_ip_address" ]; then
            # flush alias IP
            ip -4 addr flush dev ${interface} label ${interface}:0
        fi

        if [ -n "$old_ip_address" ]; then
            # flush leased IP
            ip -4 addr flush dev ${interface} label ${interface}
        fi

        if [ -n "$alias_ip_address" ]; then
            # alias IP given => set it & add host route to it
            ip -4 addr add ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
                dev ${interface} label ${interface}:0
            ip -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
        fi

        ;;

    TIMEOUT)
        if [ -n "$alias_ip_address" ]; then
            # flush alias IP
            ip -4 addr flush dev ${interface} label ${interface}:0
        fi

        # set IP from recorded lease
        ip -4 addr add ${new_ip_address}${new_subnet_mask:+/$new_subnet_mask} \
            ${new_broadcast_address:+broadcast $new_broadcast_address} \
            dev ${interface} label ${interface}

        if [ -n "$new_interface_mtu" ]; then
            # set MTU
            ip link set dev ${interface} mtu ${new_interface_mtu}
        fi

        # if there is no router recorded in the lease or the 1st router answers pings
        if [ -z "$new_routers" ] || ping -q -c 1 "${new_routers%% *}"; then
    # if we have $new_rfc3442_classless_static_routes then we have to
    # ignore $new_routers entirely
    if [ ! "$new_rfc3442_classless_static_routes" ]; then
    if [ -n "$alias_ip_address" ] &&
       [ "$new_ip_address" != "$alias_ip_address" ]; then
# separate alias IP given => set up the alias IP & add host route to it
ip -4 addr add ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
    dev ${interface} label ${interface}:0
ip -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
    fi

    # set if_metric if IF_METRIC is set or there's more than one router
    if_metric="$IF_METRIC"
    if [ "${new_routers%% *}" != "${new_routers}" ]; then
if_metric=${if_metric:-1}
    fi

    # set default route
    for router in $new_routers; do
ip -4 route add default via ${router} dev ${interface} \
    ${if_metric:+metric $if_metric} >/dev/null 2>&1

if [ -n "$if_metric" ]; then
    if_metric=$((if_metric+1))
fi
    done
    fi

            # update /etc/resolv.conf
            make_resolv_conf
        else
            # flush all IPs from interface
            ip -4 addr flush dev ${interface}
            exit_with_hooks 2
        fi

        ;;

    ### DHCPv6 Handlers
    # TODO handle prefix change: ?based on ${old_ip6_prefix} and ${new_ip6_prefix}?

    PREINIT6)
        # ensure interface is up
        ip link set ${interface} up

        # flush any stale global permanent IPs from interface
        ip -6 addr flush dev ${interface} scope global permanent

        ;;

    BOUND6|RENEW6|REBIND6)
        if [ "${new_ip6_address}" ]; then
            # set leased IP
            ip -6 addr add ${new_ip6_address} \
                dev ${interface} scope global
        fi

        # update /etc/resolv.conf
        if [ "${reason}" = BOUND6 ] ||
           [ "${new_dhcp6_name_servers}" != "${old_dhcp6_name_servers}" ] ||
           [ "${new_dhcp6_domain_search}" != "${old_dhcp6_domain_search}" ]; then
            make_resolv_conf
        fi

        ;;

    DEPREF6)
        # set preferred lifetime of leased IP to 0
        ip -6 addr change ${cur_ip6_address} \
            dev ${interface} scope global preferred_lft 0

        ;;

    EXPIRE6|RELEASE6|STOP6)
        if [ -z "${old_ip6_address}" ]; then
            exit_with_hooks 2
        fi

        # delete leased IP
        ip -6 addr del ${old_ip6_address} \
            dev ${interface}

        ;;
esac

exit_with_hooks 0
c) This part is easy:

Code: [Select]

sudo mkdir /var/db

Make sure dhclient will have everything it needs next boot! Add these lines to /opt/.filetool.lst:

Code: [Select]

etc/dhcp/dhclient.conf
sbin/dhclient-script
var/db/
And do a backup: filetool.sh -b

Now reboot and connect using the new approach. Here is the key part of my "autowifi" script (which runs with root privileges):

Code: [Select]

ssid=WorkplaceOpen
iface=wlan0
auth_file=/tmp/wifi.conf

modprobe ipv6
printf 'network={\n\tssid="%s"\n\tkey_mgmt=NONE\n}\n' $ssid > $auth_file
wpa_supplicant -i $iface -c $auth_file &
sleep 3
dhclient -v -cf /etc/dhcp/dhclient.conf $iface
I'm happy to say that using the new approach (IPv6 enabled + wpa_supplicant + dhclient) I no longer have experienced any dropped connections.

I hope this is helpful to someone.

    [EDIT]: Fixed  several  typos.  Rich

[Rich]

Hi GNUser

Backup command should have been filetool.sh -b, obviously. Sorry for the typo.

Fixed.

[GNUser]

Thanks

[GNUser]

In old version of my autowifi script there should be a sleep command (I use sleep 3) between iwconfig and udhcpc commands. In new version, sleep (again, I use sleep 3) between wpa_supplicant and dhclient commands. Gosh, sorry for the oversight.

P.S. I wish I could edit my own posts later. Why is there only a brief window of time in which a forum user can edit his own post?

[Rich]

Hi GNUser
Fixed.

[GNUser]

Thanks again. Everything looks good now.

This was a tough one to solve. With virtually no clues from my machine and no personal access to workplace's router or router settings, I was just shooting in the dark. Hopefully the write-up will be of use to someone in a similar situation.

[GNUser]

Just a quick follow-up: My original problem may have been a DHCP issue.

dhclient logs lease renewals in /var/db/dhclient.leases and I'm seeing a lease renewal every 12-15 minutes while at work. It seems that the DHCP server on workplace's router is psycho and gives out very short-lived leases. dhclient renews the lease as expected, but udhcpc was apparently not renewing the lease. Just a theory.

[Rich]

Hi GNUser

Code: [Select]

tc@box:~/tcprovides/db/10.x$ udhcpc --help
BusyBox v1.19.3 (2011-10-30 01:47:29 UTC) multi-call binary.

Usage: udhcpc [-fbnqoCRB] [-i IFACE] [-r IP] [-s PROG] [-p PIDFILE]
        [-H HOSTNAME] [-V VENDOR] [-x OPT:VAL]... [-O OPT]... [-P N]

        -i,--interface IFACE    Interface to use (default eth0)
        -p,--pidfile FILE       Create pidfile
        -s,--script PROG        Run PROG at DHCP events (default /usr/share/udhcpc/default.script)
        -B,--broadcast          Request broadcast replies
        -t,--retries N          Send up to N discover packets
        -T,--timeout N          Pause between packets (default 3 seconds)
        -A,--tryagain N         Wait N seconds after failure (default 20)
        -f,--foreground         Run in foreground
        -b,--background         Background if lease is not obtained
        -n,--now                Exit if lease is not obtained
        -q,--quit               Exit after obtaining lease
        -R,--release            Release IP on exit
        -S,--syslog             Log to syslog too
        -P,--client-port N      Use port N (default 68)
        -a,--arping             Use arping to validate offered address
        -O,--request-option OPT Request option OPT from server (cumulative)
        -o,--no-default-options Don't request any options (unless -O is given)
        -r,--request IP         Request this IP address
        -x OPT:VAL              Include option OPT in sent packets (cumulative)
                                Examples of string, numeric, and hex byte opts:
                                -x hostname:bbox - option 12
                                -x lease:3600 - option 51 (lease time)
                                -x 0x3d:0100BEEFC0FFEE - option 61 (client id)
        -F,--fqdn NAME          Ask server to update DNS mapping for NAME
        -H,-h,--hostname NAME   Send NAME as client hostname (default none)
        -V,--vendorclass VENDOR Vendor identifier (default 'udhcp VERSION')
        -C,--clientid-none      Don't send MAC as client identifier
Signals:
        USR1    Renew current lease
        USR2    Release current lease

tc@box:~/tcprovides/db/10.x$Maybe:

Code: [Select]

udhcpc -i $iface -x lease:86400

[GNUser]

Thank you, Rich. I may revert to using iwconfig and udhcpc in the future. For now they're in timeout for giving me a headache and I'm enjoying wifi simply working as expected.

If I do figure out how to make my script work with the more minimalistic tools, I'll make sure to post another follow-up. Maybe it really was just a matter of a missing option to udhcpc.

[GNUser]

I got it working with udhcpc, so here is the promised follow-up.

It turns out that udhcpc was innocent. The cause for the dropped connections must have been either missing ipv6 support or using iwconfig to establish the connection.

Here are the commands I've been using to establish a rock-solid WiFi connection anywhere:

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0. Create some variables
# iface=wlan0
# auth_file=/tmp/wifi.conf
# ssid=SomeCoolHotspot
# password=SomePassword

1. Enable ipv6 (assumes ipv6-4.19.10-tinycore64.tcz is loaded)
# modprobe ipv6

2. Create wpa_supplicant config file
    a. For open network:
        # printf 'network={\n\tssid="%s"\n\tkey_mgmt=NONE\n}\n' $ssid > $auth_file
    b. For secured network:
        # wpa_passphrase "$ssid" "$password" > $auth_file

3. Connect:
# wpa_supplicant -i $iface -c $auth_file & sleep 3

4. Get an IP address:
# udhcpc -S -i $iface
The -S flag makes udhcpc log to syslog, so to see what udhcpc has been up to just do this:

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$ cat /var/log/messages | grep udhcpc
Turns out work router gives out 30 minute leases. From syslog I see that udhcpc automatically tries to renew the lease about halfway through lease (when lease is 15 minutes old). Sometimes udhcpc fails to renew, but then it tries again about 7 minutes later (when lease is ~22 minutes old).

Hope this helps someone. I will leave a little note in the wireless section of the wiki.

[GNUser]

The issue was using iwconfig when connecting to open networks. When I use wpa_supplicant across the board (for both password-protected and open networks), there are no dropped connections.

I've been using this homebrewed script for weeks now, without any dropped connections ("Look ma, no network manager!"): https://github.com/bdantas/autowifi

P.S. udhcpc was innocent all along. Also, at least with all the networks I've tested, ipv6 support is not required for a stable wifi connection.