Quote:>I am perusing Jeff's excellent article on how to change the system name
>or IP address (which I will be doing Sunday :{
>As I was looking through the files that I will need to change I noted
>that in /etc/default/tcp, BROADCAST=xxx.yyy.171.255
>My current IP address is xxx.yyy.177.98
>Is the current BROADCAST wrong or what ?
A broadcast address depends on the subnet to which it belongs.
You have the network number at the bottom end of a range of
addresses , and a broadcast address at the top end of that range,
and all addresses between them are useable.
The network scheme is binary so the networks are in segments
divisible by two. The most common is a block of 256 numbers with
254 useable addresses. This was originally called a class C
network and now known as a /24 block.
If your broadcast address ends in .255 and your network address
ends in .98 - then you must be in full class C address range and
the broadcast would be correct. Since 98 is in the bottom 1/2 of
256 addresses and the .255 is at the top half then they must be
part of a single block of addresses.
If your address ended in .144 for example with a broadcast of
.255 then you could still be in the block of 256 addresses, or you
could be in a block of 128 starting at .128. At that point there
would not information to determine what your base network would be.
Given the .98 as your address and .255 as the broadcast, the
broadcast is correct as nothing else will fit those two numbers.
Quote:>2nd question, same subject:
>I note that /etc/rc2.d/S85tcp has a route add command with two (or
>is it 3) IP numbers following it:
>/etc/route add 224.0.0.0 xxx.yyy.177.98 0
>that is: the 224.0.0.0 address (??) my IP address and a zero.
>why is the 224....address in there ?
The 224 network range is for multicast. There are three types of
transmissions - unicast, multicast and broadcast.
Broadcast is data sent to all machines in a give subnet. Used
primarily to find a given machine.
The machine matching the query sends it's information back to the
machine that broadcast originally. Since it is directed only to
one machine this is called a unicast.
The 224 is part of a multicast range of addresses. That means that
one machine can send data out - but while it is not sending to any
specific machine - many machine can elect to receive the data.
It's just the same as if you were tuning into a radio or tv
broadcast.
You will see multicast used for such things as video conferencing,
or events occuring in real time which can be selective received by
multiple targets. This cuts down on data flowing across the net.
Otherwise you could have several machines each getting a unicast
stream and the data on the net would be the sum total off all
the individual unicast streams. There is not a lot of multicast
out there - yet.
This more properly belongs in a network discussion area.
Networking can be complex but it's quite logical after you get over
the learning curve hump. Think of it as Unix on steroids. :-)
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