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mrhillsman/dns-config.sh

Forked from odyssey4me/dns-config.sh
Created August 17, 2016 15:50
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Revisions

  1. Jesse Pretorius revised this gist Aug 17, 2016. No changes.
  2. Jesse Pretorius created this gist Aug 17, 2016.
    118 changes: 118 additions & 0 deletions dns-config.sh
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,118 @@
    #!/bin/bash

    INPUTFILE=${INPUTFILE:-'/etc/resolv.conf'}
    DEBUG=${DEBUG:-false}

    FALLBACK_NAMESERVERS_IPV4='8.8.8.8 8.8.4.4'
    FALLBACK_NAMESERVERS_IPV6='2001:4860:4860::8888 2001:4860:4860::8844'
    HOST_ADDRESSES_IPV4=$(ip a | awk '/inet / {print $2}' | grep -v '^127\.' | cut -d/ -f1 | paste -d' ' -s)
    HOST_ADDRESSES_IPV6=$(ip a | awk '/inet6 / {print $2}' | grep -v '^::' | cut -d/ -f1 | paste -d' ' -s)
    HOST_NAMESERVERS_NOLOCAL_IPV4=$(awk '/^nameserver/ {print $2}' ${INPUTFILE} | grep -v '^127\.\|^::' | grep '\.' | paste -d' ' -s)
    HOST_NAMESERVERS_NOLOCAL_IPV6=$(awk '/^nameserver/ {print $2}' ${INPUTFILE} | grep -v '^127\.\|^::' | grep ':' | paste -d' ' -s)

    WORKING_NAMESERVER_IPV6=""
    WORKING_NAMESERVERS_IPV4=""
    WORKING_NAMESERVERS_ALL=""
    BROKEN_NAMESERVERS_ALL=""

    function test_dns {
    server_list="$@"
    if ${DEBUG}; then
    >&2 echo "--> test_dns server_list: ${server_list}"
    fi
    for server in ${server_list}; do
    if ${DEBUG}; then
    >&2 echo " |--> test_dns checking server: ${server}"
    fi
    if [[ ${BROKEN_NAMESERVERS_ALL} =~ .*${server}.* ]]; then
    if ${DEBUG}; then
    >&2 echo " |--> ${server} has already been tested and did not work"
    fi
    elif [[ ${WORKING_NAMESERVERS_ALL} =~ .*${server}.* ]]; then
    if ${DEBUG}; then
    >&2 echo " |--> ${server} has already been tested and is working"
    fi
    elif $(dig +short +time=1 @${server} google.com > /dev/null); then
    if ${DEBUG}; then
    >&2 echo " |--> test_dns test to ${server} successful"
    fi
    WORKING_NAMESERVERS_ALL="${WORKING_NAMESERVERS_ALL} ${server}"
    if $(echo ${server} | grep '\.' > /dev/null); then
    WORKING_NAMESERVERS_IPV4="${WORKING_NAMESERVERS_IPV4} ${server}"
    else
    WORKING_NAMESERVERS_IPV6="${WORKING_NAMESERVERS_IPV6} ${server}"
    fi
    else
    if ${DEBUG}; then
    >&2 echo " |--> test_dns test to ${server} not successful"
    fi
    BROKEN_NAMESERVERS_ALL="${BROKEN_NAMESERVERS_ALL} ${server}"
    fi
    done
    }

    if ${DEBUG}; then
    >&2 echo -e "\n### Starting Data ###"
    >&2 echo -e "HOST_ADDRESSES_IPV4:\n${HOST_ADDRESSES_IPV4}\n"
    >&2 echo -e "HOST_ADDRESSES_IPV6:\n${HOST_ADDRESSES_IPV6}\n"
    >&2 echo -e "HOST_NAMESERVERS_NOLOCAL_IPV4:\n${HOST_NAMESERVERS_NOLOCAL_IPV4}\n"
    >&2 echo -e "HOST_NAMESERVERS_NOLOCAL_IPV6:\n${HOST_NAMESERVERS_NOLOCAL_IPV6}\n"
    fi

    # Test to see whether the configured IPV6 resolvers work
    if [ ! -z "${HOST_NAMESERVERS_NOLOCAL_IPV6}" ]; then
    test_dns ${HOST_NAMESERVERS_NOLOCAL_IPV6}
    fi

    # Test to see whether the configured IPV4 resolvers work
    if [ ! -z "${HOST_NAMESERVERS_NOLOCAL_IPV4}" ]; then
    test_dns ${HOST_NAMESERVERS_NOLOCAL_IPV4}
    fi

    if ${DEBUG}; then
    >&2 echo -e "\n### Working Name Servers after testing resolv.conf entries ###"
    >&2 echo -e "WORKING_NAMESERVERS_IPV6:\n${WORKING_NAMESERVERS_IPV6}\n"
    >&2 echo -e "WORKING_NAMESERVERS_IPV4:\n${WORKING_NAMESERVERS_IPV4}\n"
    fi

    # If none of the resolvers work, the test whether the host has
    # a working DNS service listener on one of its IPV6 addresses.
    if [ -z "${WORKING_NAMESERVERS_IPV6}" ]; then
    test_dns ${HOST_ADDRESSES_IPV6}
    fi

    # If none of the resolvers work, the test whether the host has
    # a working DNS service listener on one of its IPV4 addresses.
    if [ -z "${WORKING_NAMESERVERS_IPV6}" ]; then
    test_dns ${HOST_ADDRESSES_IPV4}
    fi

    if ${DEBUG}; then
    >&2 echo -e "\n### Working Name Servers after testing the host addresses ###"
    >&2 echo -e "WORKING_NAMESERVERS_IPV6:\n${WORKING_NAMESERVERS_IPV6}\n"
    >&2 echo -e "WORKING_NAMESERVERS_IPV4:\n${WORKING_NAMESERVERS_IPV4}\n"
    fi

    # We only implement the fallback IPV6 addresses if none of the IPV6 addresses
    # in the existing resolv.conf and none of the IPV6 host addresses worked.
    if [ -z "${WORKING_NAMESERVERS_IPV6}" ]; then
    test_dns ${FALLBACK_NAMESERVERS_IPV6}
    fi

    # We only implement the fallback IPV4 addresses if none of the IPV4 addresses
    # in the existing resolv.conf and none of the IPV4 host addresses worked.
    if [ -z "${WORKING_NAMESERVERS_IPV4}" ]; then
    test_dns ${FALLBACK_NAMESERVERS_IPV4}
    fi

    if ${DEBUG}; then
    >&2 echo -e "\n### Working Name Servers after testing the fallback addresses ###"
    >&2 echo -e "WORKING_NAMESERVERS_IPV6:\n${WORKING_NAMESERVERS_IPV6}\n"
    >&2 echo -e "WORKING_NAMESERVERS_IPV4:\n${WORKING_NAMESERVERS_IPV4}\n"
    fi

    WORKING_NAMESERVERS_ALL="${WORKING_NAMESERVERS_IPV6} ${WORKING_NAMESERVERS_IPV4}"

    for server in ${WORKING_NAMESERVERS_ALL}; do
    echo "nameserver ${server}"
    done