Mdns: mesh DNS system¶

This is an example of bmx6 SMS plugin utilization. It is a distributed DNS system where every node publish the domains it is managing.
The current implementation is done for working in OpenWRT with the Dnsmasq daemon.

Usage¶

• /etc/init.d/mdns start
• /etc/init.d/mdns start
• /etc/init.d/mdns reload

Files¶

• /etc/mdns/public contains the list of domains we wanto to announce in the network
• /etc/mdns/hosts contains a list of "IP -> domain" which have been obtained from the network (dnsmasq looks on it)

Executation¶

By default, even if there are not domains to publish in /etc/mdns/public file, the mdns script publish its own hostname.[ALL_ACCEPTED_TLDs]

The accepted TLDs can be configured in the variables DOMAINS4 and DOMAINS6, for IPv4 and IPv6 respectivelly.
So if someone publish "google.com" but your mdns instance is not accepting the ".com" TLD it will be discarted.

root@UPClab104-1677:~# /etc/init.d/mdns start
-> preparing bmx6
INFO  uci_create_section: bmx6.cfg125cb5=syncSms
INFO  uci_save_option: bmx6.cfg125cb5.syncSms=mdns
INFO  uci_save_option: bmx6.cfg125cb5.syncSms=mdns
INFO  : --syncSms                 mdns                          
-> adding addn-host entry to dnsmasq config file
-> restarting dnsmasq daemon
-> cleaning files
-> publishing own IPv4 domains: UPClab104-1677.qmp
-> publishing own IPv6 domains: UPClab104-1677.qm6
-> added remote domains google.qmp pau.qmp tita.qmp SApalafolls-ebb2.qmp = 10.228.206.65
-> added remote domains SApalafolls-ebb2.qm6 = 2012:0:0:ebb2::1

Code¶

#!/bin/sh
#    Copyright (C) 2013 Pau Escrich <p4u@dabax.net>
#
#    This program is free software; you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation; either version 2 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License along
#    with this program; if not, write to the Free Software Foundation, Inc.,
#    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
#
#    The full GNU General Public License is included in this distribution in
#    the file called "COPYING".

# Configuration variables                                     
MDNS_DIR="/etc/mdns"                                                
HOSTF="$MDNS_DIR/hosts"                                            
MY_DOMAINS="$MDNS_DIR/public"                                     
DOMAINS4="qmp" 
DOMAINS6="qm6" 
SMSF="/var/run/bmx6/sms/sendSms/mdns"                                       
SMSR="/var/run/bmx6/sms/rcvdSms"                                            
DNSMASQ="/etc/dnsmasq.conf"                                     
DNSMASQ_PID="/var/run/dnsmasq.pid" 

# Optional
IPV4="" 
IPV6="" 

start() {
    if ! cat /etc/crontabs/root | grep mdns > /dev/null; then
        echo "/10 * * * * /etc/init.d/mdns reload > /tmp/log/mdns.log" >> /etc/crontabs/root
        /etc/init.d/cron enable
        /etc/init.d/cron start
    fi
    /etc/init.d/mdns reload
    }

stop() {
    sed -i -e '/.*\/etc\/init\.d\/mdns reload > \/tmp\/log\/mdns\.log$/d' /etc/crontabs/root
    /etc/init.d/cron restart
    }

reload() {
    init
    publish_my_domains
    get_domains
    finish    
}

refresh() { 
    reload
}

# Code

error() {
    echo "ERROR: $@" 
    exit 1
}

log() {
    echo -e "-> $@" 
}

init() {
    log "preparing bmx6" 
    bmx6 -c --syncSms mdns
    [ $? -ne 0 ] && error "cannot configure bmx6 daemon" 

    cat $DNSMASQ | egrep "^addn-hosts=$HOSTF" -q || {
        log "adding addn-host entry to dnsmasq config file" 
        echo "addn-hosts=$HOSTF" >> $DNSMASQ
        log "restarting dnsmasq daemon" 
        /etc/init.d/dnsmasq restart
    }
    ps | grep dnsmasq -q || error "dnsmasq not running" 

    log "cleaning files" 
    [ -f $SMSF ] && rm -f $SMSF
    touch $SMSF

    [ -f $HOSTF ] && rm -f $HOSTF
    touch $HOSTF    

    [ ! -d $MDNS_DIR ] && mkdir -p $MDNS_DIR
    touch $MY_DOMAINS
}

check_domain() {
        local v="$1" 
        local d="$2" 
        local valid=1
        local domains="" 

        [ $v == "4" ] && domains="$DOMAINS4" 
        [ $v == "6" ] && domains="$DOMAINS6" 
        [ $v == "all" ] && domains="$DOMAINS4 $DOMAINS6" 

        for D in $domains; do
            echo "$d" | egrep "\.$D"$ -q && valid=0 && break
        done 

        return $valid
}

get_my_domains() {
    local v=${1:-4}
    local my_domains="" 
    local domains="" 
    local d

    for d in $(cat $MY_DOMAINS); do
        check_domain $v $d && my_domains="$d $my_domains" 
    done

    [ "$v" == "4" ] && domains="$DOMAINS4" 
    [ "$v" == "6" ] && domains="$DOMAINS6" 

    for d in $domains; do
        my_domains="$(cat /proc/sys/kernel/hostname).$d $my_domains" 
    done

    echo $my_domains
}

get_my_ip4() {
    [ -z $IPV4 ] && \
    bmx6 -cp | grep tun4Address | awk '{print $2}' | awk -F / '{print $1}' || \
    echo "$IPV4" 
}

get_my_ip6() {
    [ -z $IPV4 ] && \
    bmx6 -cp | grep tun6Address | awk '{print $2}' | awk -F / '{print $1}' || \
    echo "$IPV6" 
}

publish_my_domains() {
    local d domains

    local ip4="$(get_my_ip4)" 
    local ip6="$(get_my_ip6)" 

    [ -z "$ip4$ip6" ] && error "cannot get ip address" 

    [ -n "$ip4" ] && {
        domains="$(get_my_domains 4)" 
        log "publishing own IPv4 domains: $domains" 
        echo "$ip4 $domains" >> $SMSF
        echo "$ip4 $domains" >> $HOSTF
    }

    [ -n "$ip6" ] && {
        domains="$(get_my_domains 6)" 
        log "publishing own IPv6 domains: $domains" 
        echo "$ip6 $domains" >> $SMSF
        echo "$ip6 $domains" >> $HOSTF
    }
}

get_domains() {
    local f d domline ip line n i

    ls $SMSR/*:mdns 2>/dev/null >/dev/null && {

      # for each received file    
      for f in $SMSR/*:mdns; do
        n=$(cat $f | wc -l)

        # for each line inside the file
        for i in $(seq $n); do
            line=$(cat $f | awk "NR==$i")

            ip="$(echo $line | awk '{print $1}')" 
            [ -z $ip ] && continue

            domains="" 
            # for each domain (first is IP)
            for d in $(echo "$line" | awk '{$1=""; print $0}'); do
                check_domain all $d && domains="$d $domains" 
            done

            [ -n "$domains" ] && echo "$ip $domains" >> $HOSTF
            log "added remote domains $domains= $ip" 
      done
  done 

      } || log "not published domains found in the network" 
}

finish() {
    kill -SIGHUP $(cat $DNSMASQ_PID)
}

$@