November 17th, 2008
Network connections fail all the time, we've all been there. There are so many things that can go wrong, the network adapter driver can fail, the dhcp server can revoke the lease, the wifi router can disappear, the routing may be wrong at some point along the line, the dns server can be overloaded, or the remote host may be down. Those are some of the possibilities, and it can be quite a pain to track down the problem.
But the first thing to do is to figure out exactly what is working and what isn't. If you know that much then at least you know where to start. My goal here is to create a fairly simple test to examine the status of the network connection, leading up to a working internet connection. One constraint that I have is that I like it to be portable, so that I can carry it around along with my dotfiles. That means I would like it to work in any location just as long as I can get a shell, it should not require any dependencies.
A fully functional network connection looks like this:
What I do is try to detect the parameters of the network step by step, using the regular tools like route, ifconfig. Once I know what the hosts are, I do a ping. Now, a ping obviously isn't a foolproof test; if you're on a network that doesn't allow outgoing icmp then it's entirely possible that you can tcp out anyway. So what you really should do is tcp on port 80, not ping. But ping is extremely portable, whereas doing a tcp/udp probe is asking a lot more from the environment, needing something like nmap or hping.
Once you've established that the connection is working, and you want to know more about the network, you can go further with something like netscan.
The code is relatively stupid and messy, but that's the way bash is.
# Author: Martin Matusiak <numerodix@gmail.com>
# Licensed under the GNU Public License, version 3
function havenet {
local init="$(toolsinit)"
platforminit
case "$PLATFORM" in
"Linux")
echo "Platform: $PLATFORM"
run_havenet "$init";;
*)
echo "Platform: $PLATFORM (local network detection not supported)"
run_haveinet "$init";;
esac
}
function haveinet {
local init="$(toolsinit)"
platforminit
echo "Platform: $PLATFORM"
run_haveinet "$init"
}
function platforminit {
if $(which uname &>/dev/null); then
PLATFORM=$(uname 2>/dev/null)
fi
}
function toolsinit {
local tools="true"
local missing=()
local cmds=(/sbin/route /sbin/ifconfig ping nmap)
local args=(" -n" "" " -c1 -W2" " -T3")
local names=(route ifconfig ping nmap)
local i=-1
while [ $i -lt $(( ${#names[@]} - 1 )) ]; do i=$(( $i+1 ))
if [ 0 -eq $(which ${cmds[$i]} &>/dev/null ; echo $?) ]; then
tools="$tools;local ${names[$i]}=\"${cmds[$i]}${args[$i]}\""
else
missing[${#missing[@]}]="${cmds[$i]}"
fi
done
if [ ${#missing[@]} -gt 0 ]; then
echo -e "Missing tools: ${cred}${missing[*]}${creset}" 1>&2
fi
echo "$tools"
}
function run_havenet {
eval "$@"
local localranges="169.254 10 172.(1[6-9]|2[0-9]|3[0-1]) 192.168"
### Scan networks
echo -e "${cyellow} + Scanning for networks...${creset}"
test=$($route 2>/dev/null | egrep "^[1-9]")
if [[ $? != 0 ]]; then
echo -e " ${cred}none found${creset}"
else
local nets=$(echo "$test" | sort | awk '{ print $1 }')
for net in $nets; do
local gw=$($route 2>/dev/null | egrep "^$net" | awk '{ print $3 }')
printf " ${cgreen}%-15s${creset} ${ccyan}%s${creset}\n" "$net" "/ $gw"
done
### Detect ips
local ips=
for net in $nets; do
local r=$(echo $net | sed "s/.0$//g" | sed "s/.0$//g" | sed "s/.0$//g")
local ip=$($ifconfig 2>/dev/null | grep "inet addr:$r" | sed "s/inet addr:\([0-9.]*\).*$/\1/g")
ips="$ip $ips"
done
echo -e "${cyellow} + Detecting ips...${creset}"
test=$(echo "$ips" | egrep -v "^[ ]+$")
if [[ $? != 0 ]]; then
echo -e " ${cred}none found${creset}"
else
local on_lan=1
for ip in $ips; do
printf " ${cgreen}%-15s${creset} %s" "$ip" "ping: "
test=$($ping $ip 2>/dev/null)
if [[ $? != 0 ]]; then
echo -e "${cred}failed${creset}"
else
local t=$(echo "$test" | grep "min/avg" | sed "s/.*= \([0-9.]*\)\/.*$/\1/g")
echo -e "${cgreen}$t ms${creset}"
fi
### Test ips for lan
local ip_on_lan=0
for prefix in $localranges; do
test=$(echo "$ip" | egrep "^$prefix" 2>/dev/null)
if [[ $? == 0 ]]; then
ip_on_lan=1
fi
done
on_lan=$(( $on_lan & $ip_on_lan ))
done
if [ $on_lan -eq 1 ]; then
### Detect gateways if on lan
echo -e "${cyellow} + Detecting gateways (network is local)...${creset}"
test=$($route 2>/dev/null | grep UG)
if [[ $? != 0 ]]; then
echo -e " ${cred}none found${creset}"
else
local gws=$(echo "$test" | awk '{ print $2 }')
for gw in $gws; do
printf " ${cgreen}%-15s${creset} %s" "$gw" "ping: "
test=$($ping $gw 2>/dev/null)
if [[ $? != 0 ]]; then
echo -e "${cred}failed${creset}"
else
local t=$(echo "$test" | grep "min/avg" | sed "s/.*= \([0-9.]*\)\/.*$/\1/g")
echo -e "${cgreen}$t ms${creset}"
fi
done
### Try inet connection if we have a gateway
run_haveinet "$@"
fi
else
### Try inet connection, we're on wan
run_haveinet "$@"
fi
fi
fi
}
function run_haveinet {
eval "$@"
local rootname="A.ROOT-SERVERS.NET."
local rootip="198.41.0.4"
local dnsport="53"
local inethosts="yahoo.com google.com"
local inetport="80"
### Test inet connection
echo -e "${cyellow} + Testing internet connection...${creset}"
echo -en " ${ccyan}$rootname ${cgreen}$rootip${creset} ping: "
test=$($ping $rootip 2>/dev/null)
if [[ $? != 0 ]]; then
echo -e "${cred}failed${creset}"
else
local t=$(echo "$test" | grep "min/avg" | sed "s/.*= \([0-9.]*\)\/.*$/\1/g")
echo -e "${cgreen}$t ms${creset}"
fi
### Detect dns
echo -e "${cyellow} + Detecting dns servers...${creset}"
test=$(cat /etc/resolv.conf 2>/dev/null | grep ^nameserver)
if [[ $? != 0 ]]; then
echo -e " ${cred}none found${creset}"
else
local dnss=$(echo "$test" | awk '{ print $2 }')
for dns in $dnss; do
printf " ${cgreen}%-15s${creset} %s" "$dns" "ping: "
test=$($ping $dns 2>/dev/null)
if [[ $? != 0 ]]; then
echo -en "${cred}failed${creset}"
else
local t=$(echo "$test" | grep "min/avg" | sed "s/.*= \([0-9.]*\)\/.*$/\1/g")
echo -en "${cgreen}$t ms${creset}"
fi
local proto="tcp" ; local udpflags=""
if [[ `whoami` = "root" ]]; then
proto="udp"; udpflags="-sU -PN"
fi
echo -en " dns/$proto: "
test=$($nmap $dns $udpflags -p $dnsport 2>/dev/null)
if ! echo "$test" | grep "$dnsport/$proto" | grep "open" &>/dev/null; then
echo -e "${cred}failed${creset}"
else
local t=$(echo "$test" | grep "scanned in" | sed "s/^.*in \([0-9.]*\) seconds.*$/\1/g")
t=$(echo $t*1000 | bc)
echo -e "${cgreen}$t ms${creset}"
fi
done
fi
### Test inet dns
echo -e "${cyellow} + Testing internet dns...${creset}"
for inethost in $inethosts; do
printf " ${cgreen}%-15s${creset} %s" "$inethost" "ping: "
test=$($ping $inethost 2>/dev/null)
if [[ $? != 0 ]]; then
echo -en "${cred}failed${creset}"
else
local t=$(echo "$test" | grep "min/avg" | sed "s/.*= \([0-9.]*\)\/.*$/\1/g")
echo -en "${cgreen}$t ms${creset}"
fi
echo -en " http: "
test=$($nmap $inethost -p $inetport 2>/dev/null)
if ! echo "$test" | grep "$inetport/tcp" | grep "open" &>/dev/null; then
echo -e "${cred}failed${creset}"
else
local t=$(echo "$test" | grep "scanned in" | sed "s/^.*in \([0-9.]*\) seconds.*$/\1/g")
t=$(echo $t*1000 | bc)
echo -e "${cgreen}$t ms${creset}"
fi
done
}
UPDATE: Replacing with newer version that is a bit more clever.
UPDATE2: Added tool detection and platform detection.
