1. Introduction

Google has explained here how to verify if a given IP address belongs to Googlebot. So instead of hard-coding all the IPs which might change eventually, Google has suggested doing a DNS lookup using a host command on Linux. The steps suggested in the article are:

1. Reverse DNS lookup using the IP to get the domain name.
2. Check if the domain name contains googlebot.com or google.com. The types of bots and their names can be found here.
3. Forward DNS lookup using the domain name obtained in step 1 to get the IP and verify that this IP is same as the IP you initially started with.

2. Implementation Approach

And I wanted to check if the IPs ( I had around 45) belonged to google bot. One option was to run host for each of the IPs, as suggested in the above steps, but this was practically not possible and if possible it would be time-consuming. So I came up with a simple shell script to do this job.

1. Reverse DNS lookup to get the domain name:

   #hostName is the complete domain name
   hostName = host $line | cut -d" " -f 5

So a sample response of host command would be:  246.66.249.66.in-addr.arpadomain name pointer crawl-66-249-66-246.googlebot.comAnd we can extract the domain name using the cut command as shown above. This gives us: hostName = crawl-66-249-66-246.googlebot.com .

2. Forward DNS lookup to get the IP:

   hostIp=host $hostName | cut -d" " -f 4

   
   A sample response to the host command, in this case, would be: crawl-66-249-66-246.googlebot.com has address 66.249.66.246. And we extract the IP using the cut command shown above which gives us the  hostIp = 66.249.66.246 .
3. Verify the domain name to contain the Googlebot and the IP obtained in step 2 is the same as the IP we started with in step 1:

   if [ $line == $hostIp ] && [ $domainName == "googlebot.com" ]
   then
       echo "Googlebot: $hostIp -> $hostName"
   fi

3. Complete Shell Script

Let the IPs be in the file googlebots, for example, and let us add these IPs:

66.249.66.246
66.249.66.97
66.249.64.12

The shell script is given below:

#!/bin/sh
file="googlebots"
while read -r line
do
    hostName=`host $line | cut -d" " -f 5`
    domainName=`echo $hostName | cut -d"." -f2,3`
    #echo $domainName
    #echo "$hostName"
    hostIp=`host $hostName | cut -d" " -f 4`
    #echo "$hostIp"
    if [ $line == $hostIp ] && [ $domainName == "googlebot.com" ]
    then
        echo "Googlebot: $hostIp -> $hostName"
    fi
done < "$file"