HPUX conforms to the RFC-1122 guidelines on IP's and Subnetting.  This RFC 
will not allow you to assign an IP address to an interface from the zero 
subnet i.e. x.x.x.0. (x=non zero value).If you attemp this you are using a 
IP Address/Subnet Mask that violates RFC-1122 and this address will not 
appear in the table if you issue nstat -rn, you will only see the loop back 
address 127.0.0.0. There is a variable that can be changed which disables 
the checking for conformance to the RFC.  The only resolution is to disable 
the IP/Subnet conformance incorporated into the HPUX platform or set the 
interface manually by putting a script in /sbin/rc2.d simply name it 
starting with a "S".  e.g. "Setlan"


When using ip schemes that do not conform to RFC-1122 there is a
variable that can be changed which disables the checking for conformance
to the RFC.

RESOLUTION

Issue the following command on HP-UX 11.0:

ndd -h unsupported | more

The variable ip_check_subnet_addr - Controls the subnet portion of a host address

To bypass RFC-1122 address checking, set the ip_check_subnet_addr
variable to zero.  To make this a permanent setting, include this
setting in the /etc/rc.config.d/nddconf file.

Summary:

The following output is what is seen if you are checking subnets:

# ndd -get /dev/ip ip_check_subnet_addr 1

Set value

# ndd -set /dev/ip ip_check_subnet_addr 0

Now reread the netconf and nddconf files:

# /sbin/init.d/net start

To make this permanent edit /etc/rc.config.d/nddconf and add a set of lines:

TRANSPORT_NAME[0]=ip
NDD_NAME[0]=ip_check_subnet_addr
NDD_VALUE[0]=0

Also add the line, "/usr/bin/ndd  -c" after the line "usr/bin/ndd  -a"
in the /sbin/init.d/net.init script.

On HP-UX 10.20:

With HP-UX 10.20 use the nettune command to make this change

/usr/contrib/bin/nettune -s ip_check_subnet_addr 0

To make the change permanent:

1. Create a text file called nettune_script with the following line:

        /usr/contrib/bin/nettune -s ip_check_subnet_addr 0

2. mv  nettune_script  /sbin/init.d/nettune_script
3. chmod  555  /sbin/init.d/nettune_script
4. chgrp  bin  /sbin/init.d/nettune_script
5. chown  bin  /sbin/init.d/nettune_script
6. cd  /sbin/rc2.d
7. ln  -s  /sbin/init.d/nettune_script  /sbin/rc2.d/S006subnet


-Contributed by Corey Harris