ping from script launched by cron

I found that it can not ping from the shell script launched by cron. I wrote shell script like this:

#!/bin/bash

ping localhost
echo "Exit status: $?" >> /tmp/ping.log

And I configured crontab so that this script is executed at every minutes.

crontab -e
# I wrote * * * * * /path/to/the/script

In some minutes, I checked the file /tmp/ping.log. According to the log, the status code of ping was 127, indicating it failed. When I execute ping in usual interactive shell by hand, It succeeds. Why does it fail from cron ?