Broadcast address

[Andrew Crowe_2]

Have just migrated to a new network for all of our HP9000 servers(mostly HP-UX 10.20).
What is the effect of the fact that the broadcast address still using an IP from the old network and how can I change the broadcast address?

Thanks for any help

[Ravi_8]

Hi,

If all your systems are on NIS/DNS then broadcast matters otherwise doesn't.
However if u change the IP then you need to modify the same in /etc/hosts and /etc/rc.config.d/netconf file

[Andrew Crowe_2]

Thanks for your reply

I don't use DNS or NIS as I only have a couple of servers. Does the broadcast address have any effect on the server?

[U.SivaKumar_2]

Hi,
It is advised to set the broadcast address for
the networks . Otherwise it will take 255.255.255.255 as the default broadcast address and will cause weird problems in some
networking servers like samba etc.

regards,
U.SivaKumar

[U.SivaKumar_2]

Hi,
sorry Iam wrong in my previous post. If you
don't set any broadcast address. example for
ip address 90.0.0.1 and mask 255.0.0.0 by
default 90.255.255.255 is taken as broadcast
address.

regards,
U.SivaKumar

[T G Manikandan · Accepted solution]

To my knowlegge if you are changing to your new network ip,the broadcast address should be different.
Broadcast address is a communication from one point on the lan to all other points i.e. one machine broadcasting to other machines on the same LAN.

I is useful in the address resolution protocol (arp) where a system gets a broadcast from a point and makes an entry that is x.x.x.x ip has the ethernet address as 00:3c:4b:...
You can change the broadcast address in your /etc/rc.config.d/netconf file.
But whenever you configure your machine with a ip-address and the subnet mask the system automatically assigns a broadcast address by

doing a AND on the network ID and the subnet mask of the machine.

Though this is done by the system you can check your /etc/rc.config.d/netconf file for the correct values for the parameter
BROADCAST_ADDRESS

However the implications are
if a wrong broadcast address is assigned to a machine the machine may do a broadcast storm and this might cripple your network.


thanks