Network Troubleshooting script

#!/bin/sh
# Network testing script v 1.0
# (c) 2005 Javier Fernandez-Sanguino
#
# This script will test your system's network configuration using basic
# tests and providing both information (INFO messages), warnings (WARN)
# and possible errors (ERR messages) by checking:
# - Interface status
# - Availability of configured routers, including the default route
# - Proper host resolution, including DNS checks
# - Proper network connectivity (the remote host can be configured, see
# below)
#
# The script does not need special privileges to run as it does not
# do any system change. It also will not fix the errors by itself.
#
# 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#
# You can also find a copy of the GNU General Public License at
# http://www.gnu.org/licenses/licenses.html#TOCLGPL
#
# TODO
# - Works only on Linux, can this be generalised for other UNIX systems
# (probably not unless rewritten in C)
# - Does not check for errors properly, use -e and test intensively
# so that expected errors are trapped
# (specially for tools that are not available, like netcat)
# - If the tools are localised to languages != english the script might
# break
# - Ask 'host' maintainer to implement error codes as done with
# dlint
# - Should be able to check if DNS server is in the same network, if
# it doesn't answer to pings, check ARP in that case.
# - DHCP checks?
# - Other internal services tests? (LDAP if using pam...)
# - Generate summary of errors in the end (pretty report?)
# - Check if packets are being dropped by local firewall? (use dmesg
# and look for our tests)
# - Support wireless interfaces? (use iwconfig)
# - Check other TODOs inline in the code


# BEGIN configuration
# Configure to your needs, these values will be used when
# checking DNS and Internet connectivity
# DNS name to resolve
CHECK_HOST=www.debian.org
CHECK_IP_ADRESS=194.109.137.218
# Web server to check for
CHECK_WEB_HOST=www.debian.org
CHECK_WEB_PORT=80
export CHECK_HOST CHECK_IP_ADRESS CHECK_WEB_HOST CHECK_WEB_PORT
# END configuration


# Extract the interface of our default route

defaultif=`netstat -nr |grep ^0.0.0.0 | awk '{print $8}' | head -1`
defaultroutes=`netstat -nr |grep ^0.0.0.0 | wc -l`
if [ -z "$defaultif" ] ; then
defaultif=none
echo "WARN: This system does not have a default route"
elif [ "$defaultroutes" -gt 1 ] ; then
echo "WARN: This system has more than one default route"
else
echo "INFO: This system has exactly one default route"
fi



# Check loopback
check_local () {
# Is there a loopback interface?
if [ -n "`ip link show lo`" ] ; then
# OK, can we ping localhost
if ! check_host localhost 1; then
# Check 127.0.0.1 instead (not everybody uses this IP address however,
# although its the one commonly used)
if ! check_host 127.0.0.1 1; then
echo "ERR: Cannot ping localhost (127.0.0.1), loopback is broken in this system"
else
echo "ERR: Localhost is not answering but 127.0.0.1, check /etc/hosts and verify localhost points to 127.0.0.1"
fi
else
echo "INFO: Loopback interface is working properly"
fi

else
echo "ERR: There is no loopback interface in this system"
status=1
fi
status=0
return $status
}

# Check network interfaces
check_if () {
ifname=$1
status=0
[ -z "$ifname" ] && return 1
# Find IP addresses for $ifname
inetaddr=`ip addr show $ifname | grep inet | awk '{print $2}'`
if [ -z "$inetaddr" ] ; then
echo "WARN: The $ifname interface does not have an IP address assigned"
status=1
else
# TODO: WARN if more than 2 IP addresses?
echo $inetaddr | while read ipaddr; do
echo "INFO: The $ifname interface has IP address $ipaddr assigned"
done
fi

# Lookup TX and RX statistics
# TODO: This is done using ifconfig but could use /proc/net/dev for
# more readibility or, better, 'netstat -i'
txpkts=`ifconfig $ifname | awk '/RX packets/ { print $2 }' |sed 's/.*://'`
rxpkts=`ifconfig $ifname | awk '/RX packets/ { print $2 }' |sed 's/.*://'`
txerrors=`ifconfig $ifname | awk '/TX packets/ { print $3 }' |sed 's/.*://'`
rxerrors=`ifconfig $ifname | awk '/RX packets/ { print $3 }' |sed 's/.*://'`
# TODO: Check also frames and collisions, to detect faulty cables
# or network devices (cheap hubs)
if [ "$txpkts" -eq 0 ] && [ "$rxpkts" -eq 0 ] ; then
echo "ERR: The $ifname interface has not tx or rx any packets. Link down?"
status=1
elif [ "$txpkts" -eq 0 ]; then
echo "WARN: The $ifname interface has not transmitted any packets."
elif [ "$rxpkts" -eq 0 ] ; then
echo "WARN: The $ifname interface has not received any packets."
else
echo "INFO: The $ifname interface has tx and rx packets."
fi
# TODO: It should be best if there was a comparison with tx/rx packets.
# a few errors are not uncommon if the card has been running for a long
# time. It would be better if a relative comparison was done (i.e.
# less than 1% ok, more than 20% warning, over 80% major issue, etc.)
if [ "$txerrors" -ne 0 ]; then
echo "WARN: The $ifname interface has tx errors."
fi
if [ "$rxerrors" -ne 0 ]; then
echo "WARN: The $ifname interface has rx errors."
fi
return $status
}

check_netif () {
status=0
ip link show | egrep '^[[:digit:]]' |
while read ifnumber ifname status extra; do
ifname=`echo $ifname |sed -e 's/:$//'`
if [ -z "`echo $status | grep UP\>`" ] ; then
if [ "$ifname" = "$defaultif" ] ; then
echo "ERR: The $ifname interface that is associated with your defualt route is down!"
status=1
elif [ "$ifname" = "lo" ] ; then
echo "ERR: Your lo inteface is down, this might cause issues with local applications (but not necessarily with network connectivity)"
else
echo "WARN: The $ifname interface is down"
fi
else
# Check network routes associated with this interface
echo "INFO: The $ifname interface is up"
check_if $ifname
check_netroute $ifname
fi
done
return $status
}

check_netroute () {
ifname=$1
[ -z "$ifname" ] && return 1
netstat -nr | grep "${ifname}$" |
while read network gw netmask flags mss window irtt iface; do
# For each gw that is not the default one, ping it
if [ "$gw" != "0.0.0.0" ] ; then
if ! check_router $gw ; then
echo "ERR: The default route is not available since the default router is unreachable"
fi
fi
done
}

check_router () {
# Checks if a router is up
router=$1
[ -z "$router" ] && return 1
status=0
# First ping the router, if it does not answer then check arp tables and
# see if we have an arp. We use 5 packets since it is in our local network.
ping -q -c 5 "$router" >/dev/null 2>&1
if [ "$?" -ne 0 ]; then
echo "WARN: Router $router does not answer to ICMP pings"
# Router does not answer, check arp
routerarp=`arp -n | grep "^$router" | grep -v incomplete`
if [ -z "$routerarp" ] ; then
echo "ERR: We cannot retrieve a MAC address for router $router"
status=1
fi
fi
if [ "$status" -eq 0 ] ; then
echo "INFO: The router $router is reachable"
fi
return $status
}

check_host () {
# Check if a host is reachable
# TODO:
# - if the host is in our local network (no route needs to be used) then
# check ARP availability
# - if the host is not on our local network then check if we have a route
# for it
host=$1
[ -z "$host" ] && return 1
# Use 10 packets as we expect this to be outside of our network
COUNT=10
[ -n "$2" ] && COUNT=$2
status=0
ping -q -c $COUNT "$host" >/dev/null 2>&1
if [ "$?" -ne 0 ]; then
echo "WARN: Host $host does not answer to ICMP pings"
status=1
else
echo "INFO: Host $host answers to ICMP pings"
fi
return $status
}

check_dns () {
# Check the nameservers defined in /etc/resolv.conf
status=1
nsfound=0
nsok=0
tempfile=`mktemp tmptestnet.XXXXXX` || { echo "ERR: Cannot create temporary file! Aborting! " >&2 ; exit 1; }
trap " [ -f \"$tempfile\" ] && /bin/rm -f -- \"$tempfile\"" 0 1 2 3 13 15
cat /etc/resolv.conf |grep nameserver |
awk '/nameserver/ { for (i=2;i<=NF;i++) { print $i ; } }' >$tempfile
for nameserver in `cat $tempfile`; do
nsfound=$(( $nsfound + 1 ))
echo "INFO: This system is configured to use nameserver $nameserver"
check_host $nameserver 5
if check_ns $nameserver ; then
nsok=$(( $nsok +1 ))
else
status=$?
fi
done
#Could also do:
#nsfound=`wc -l $tempfile | awk '{print $1}'`
/bin/rm -f -- "$tempfile"
trap 0 1 2 3 13 15
if [ "$nsfound" -eq 0 ] ; then
echo "ERR: The system does not have any nameserver configured"
else
if [ "$status" -ne 0 ] ; then
if [ "$nsfound" -eq 1 ] ; then
echo -e "ERR: There is one nameserver configured for this system but it does not work properly"
else
echo "ERR: There are $nsfound nameservers configured for this system and none of them works properly"
fi
else
if [ "$nsfound" -eq 1 ] ; then
echo "INFO: The nameserver configured for this system works properly"
else
echo "INFO: There are $nsfound nameservers is configured for this system and $nsok are working properly"
fi
fi
fi
return $status
}

check_ns () {
# Check the nameserver using host
# TODO: use nslookup?
# nslookup $CHECK_HOST -$nameserver
nameserver=$1
[ -z "$nameserver" ] && return 1
status=1
CHECK_RESULT="$CHECK_HOST .* $CHECK_IP_ADDRESS"
# Using dnscheck:
dnscheck=`host -t A $CHECK_HOST $nameserver 2>&1 | tail -1`
if [ -n "`echo $dnscheck |grep NXDOMAIN`" ] ; then
echo "ERR: Dns server $nameserver does not resolv properly"
elif [ -n "`echo $dnscheck | grep \"timed out\"`" ] ; then
echo "ERR: Dns server $nameserver is not available"
elif [ -z "`echo $dnscheck | egrep \"$CHECK_RESULT\"`" ] ; then
echo "WARN: Dns server $nameserver did not return the expected result for $CHECK_HOST"
else
echo "INFO: Dns server $nameserver resolved correctly $CHECK_HOST"
status=0
fi

# Using dlint
# dlint $CHECK_HOST @$nameserver >/dev/null 2>&1
# if [ $? -eq 2 ] ; then
# echo "ERR: Dns server $nameserver does not resolv properly"
# elif [ $? -ne 0 ]; then
# echo "ERR: Unexpected error when testing $nameserver"
# else
# echo "INFO: Dns server $nameserver resolved correctly $CHECK_HOST"
# status=0
# fi

return $status
}

check_conn () {
# Checks network connectivity
if ! check_host $CHECK_WEB_HOST >/dev/null ; then
echo "WARN: System does not seem to reach Internet host $CHECK_WEB_HOST through ICMP"
else
echo "INFO: System can reach Internet host $CHECK_WEB_HOST"
fi
# Check web access, using nc
echo -e "HEAD / HTTP/1.0\n\n" |nc $CHECK_WEB_HOST $CHECK_WEB_PORT >/dev/null 2>&1
if [ $? -ne 0 ] ; then
echo "WARN: Cannot access web server at Internet host $CHECK_WEB_HOST"
else
echo "INFO: System can access web server at Internet host $CHECK_WEB_HOST"
fi
}

# TODO: checks could be conditioned, i.e. if there is no proper
# interface setup don't bother with DNS and don't do some Inet checks
# if DNS is not setup properly
check_local
check_netif
check_dns
check_conn

exit 0


Wireless Troubleshooting guide can also be scripted
http://www.ubuntugeek.com/how-to-troubleshoot-wireless-network-connection-in-ubuntu.html