ping can not recognize host but host command can

Applications IP Networking
1

Hi,

I have a weird problem.
when ever I do ping command like for example

ping unix.com

I get the following message:

[root@localhost ~]# ping unix.com
ping: unknown host unix.com

but when I use host the computer is able to know the host.

[root@localhost ~]# host unix.com
unix.com has address 81.17.242.186
unix.com mail is handled by 10 aspmx2.googlemail.com.
unix.com mail is handled by 10 aspmx3.googlemail.com.
unix.com mail is handled by 10 aspmx4.googlemail.com.
unix.com mail is handled by 10 aspmx5.googlemail.com.
unix.com mail is handled by 1 aspmx.l.google.com.
unix.com mail is handled by 5 alt1.aspmx.l.google.com.
unix.com mail is handled by 5 alt2.aspmx.l.google.com.

what is the reason?
why the ping can not recognize the host but the host command can?

2

further to the same problem, why does nslookup unix.com return 192.168.100.5 and ping unix.com tries 207.139.nnn.nnn?

3

may be this is the problem -

from man page of ping -

argument of inet, IPv4 is used. For inet6, IPv6 is used.

            By default, if the name of a  host  is  provided,not   the  literal  IP  address,  and a valid IPv6 address exists in the name service database, ping will  use  this  address.  Otherwise, if the name service database contains  an  IPv4  address,  it will try the IPv4 address.

            Specify the address family inet or inet6 to override the default behavior. If the argument specified is inet, ping  will  use  the  IPv4  address associated  with  the  host name. If none exists, ping will state that  the  host  is  unknown  and exit.  It  does  not  try to determine if an IPv6 address exists in the name service database.

            If the specified argument is inet6, ping uses the IPv6  address  that  is  associated with the host name. If none exists, ping states that  the  host is unknown and exits.