Trying to calculate Network Address with shell script

Adanos · 11-08-2008, 04:45 PM

Hi

I'm trying to make an automated firewall script that gets all the info
like ip, netmask, network address from config files.

I got it all working exept calculating the Network Address.

#! /bin/sh

LAN_IF="eth0"
LAN_IF_IP=`ifconfig $LAN_IF | grep inet | cut -d : -f 2 | cut -d ' ' -f 1`
LAN_NETMASK=`ifconfig $LAN_IF | grep Mask | cut -d : -f 4 | cut -d ' ' -f 1`

TMP1=`echo $LAN_IF_IP | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\1/'`
TMP2=`echo $LAN_IF_IP | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\2/'`
TMP3=`echo $LAN_IF_IP | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\3/'`
TMP4=`echo $LAN_IF_IP | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\4/'`

# IP ADD as bin
TEMP1=`echo -e "obase=2; ${TMP1}" | bc | tr -d "\n" `
TEMP2=`echo -e "obase=2; ${TMP2}" | bc | tr -d "\n" `
TEMP3=`echo -e "obase=2; ${TMP3}" | bc | tr -d "\n" `
TEMP4=`echo -e "obase=2; ${TMP4}" | bc | tr -d "\n" `

TEST_NETWORK_ADD="$TEMP1 $TEMP2 $TEMP3 $TEMP4"

TMP1=`echo $LAN_NETMASK | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\1/'`
TMP2=`echo $LAN_NETMASK | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\2/'`
TMP3=`echo $LAN_NETMASK | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\3/'`
TMP4=`echo $LAN_NETMASK | sed 's/$.*$\.$.*$\.$.*$\.$.*$/\4/'`

# Subnet as bin
TEMP1=`echo -e "obase=2; ${TMP1}" | bc | tr -d "\n" `
TEMP2=`echo -e "obase=2; ${TMP2}" | bc | tr -d "\n" `
TEMP3=`echo -e "obase=2; ${TMP3}" | bc | tr -d "\n" `
TEMP4=`echo -e "obase=2; ${TMP4}" | bc | tr -d "\n" `

TEST_NETMASK="$TEMP1 $TEMP2 $TEMP3 $TEMP4"

echo "Test: IP ADDRESS $LAN_IF_IP"
echo "Test: NETMASK $LAN_NETMASK"
echo "Test: IP ADDRESS as bin: $TEST_NETWORK_ADD"
echo "Test: NETMASK as bin: $TEST_NETMASK"

Output:
Test: IP ADDRESS 10.0.0.2
Test: NETMASK 255.255.255.224
Test: IP ADDRESS as bin: 1010 0 0 10
Test: NETMASK as bin: 11111111 11111111 11111111 11100000

The fist problem im having is that the output isn't displaying as 8 digits. ex. 00001010 insted of 1010

The 2nd problem is that im not sure how to do the and'ing of the netmaks and ip address to find the network address.

Is there a better way of doing this calculation ?
any help is appreciated.

I hope the code above makes sense, im not very good at this

regards,
Adanos

acid_kewpie · 11-08-2008, 04:50 PM

do you not just want to be using the ipcalc shell tool to do all this for you?

Adanos · 11-08-2008, 04:57 PM

i'll do some resurge on that tool, thats properly what i need.
thanks for your help acid_kewpie.

PTrenholme · 11-08-2008, 05:10 PM

Doesn't the obase=2 give you binary? Your output certainly looks like binary values . . .

<edit>Oops! Sorry, I read too fast.

</edit>

Adanos · 11-09-2008, 04:07 AM

Quote:

Originally Posted by PTrenholme

Doesn't the obase=2 give you binary? Your output certainly looks like binary values . . .

yes obase=2 gives binary. You can use obase=8 and obase16 aswell for oct and hex.

keefaz · 11-09-2008, 10:37 AM

Quote:

Originally Posted by Adanos

The fist problem im having is that the output isn't displaying as 8 digits. ex. 00001010 insted of 1010

You can make your own function for displaying binary numbers,
for example, using bash:

Code:

function echo_bin()
{
  for ((mask=128; mask>0; mask>>=1)); do
    echo -n $((($1 & $mask) ? 1: 0))
  done
}

myIP="10.0.0.3"

TMP1=$(echo $myIP | cut -d. -f1)
TMP2=$(echo $myIP | cut -d. -f2)
TMP3=$(echo $myIP | cut -d. -f3)
TMP4=$(echo $myIP | cut -d. -f4)

echo "IP in dec: $myIP"
echo -n "IP in bin: "
echo -n $(echo_bin $TMP1).$(echo_bin $TMP2).$(echo_bin $TMP3).$(echo_bin $TMP4)
echo