Broadcast address

[nitinkgoud]

Hi Guys,
What is the significance of broadcast address?
I know it is generated automatically from IP address and Netmask.
How do i update it manually? And how do i make the changes permenanat.

Please help.

 

[coffeysm]

Broadcast addresses are used if something needs to be sent out to everyone on the network. It usually is not wise to change it unless your network is subnetted since it always defaults to xxx.xxx.xxx.255/24.

 

[Annihilannic]

...always defaults to xxx.xxx.xxx.255/24.

I don't think that's correct, coffey. I believe it should be the result of the logical operation:

( NOT <netmask> ) OR <ip address>

So for e.g. 123.45.65.89/22:
[tt]
IP = 01111011.00101101.01000001.01011001
Netmask = 11111111.11111111.11111100.00000000
NOT Netmask = 00000000.00000000.00000011.11111111
Broadcast = 01111011.00101101.01000011.11111111
Decimal = 123. 45. 67. 255[/tt]



Annihilannic.

 

[coffeysm]

I meant that unless you are setting up specific netmasks or subnetting your network, then it will default to xxx.xxx.xxx.255 if you are on a Class C.

 

[tjlst15]

Coffey's correct. Broadcast will contact every host that is live on the network. To answer your question, as long as you set your netmask correct, ifconfig will interpret the broadcast address if you give the +broadcast option. For example, let's say you have a host with the following info:

IP - 10.124.75.40
Netmask - 255.255.255.0

You would have to edit your /etc/hostname.<interface> to look like this:

10.124.75.40 -netmask 255.255.255.0 +broadcast

This will automatically fill in the broadcast based on the netmask, and it will apply on reboot.