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+1 vote
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In  L.B.A.  ,  we send message from a host to all host in the same network.

if NID=11.0.0.0  then a/c to definition of L.B.A we should write it as 11.255.255.255

but we write 255.255.255.255 , so it means we send message from a host to entire world's network host , which is wrong a/c to definition??????
in Computer Networks by Junior (765 points) | 630 views

3 Answers

+4 votes
255.255.255.255 is a limited broadcast: it is not passed on by routers, so it is really useful only to a member of a LAN to contact all other members of the same LAN.

But routers will not forward these broadcasts because, if they did, these broadcasts would fill the whole internet. So they are useful, in Layer-3, and limited.

Directed broadcasts are represented by, for instance, 192.168.1.255. These are passed on by routers, because of course they are less invasive than 255.255.255.255, even though this feature is often disabled in real-world routers because it is easily abused (you'll see why in a second). If I am a member of of the subnet 192.168.1.0/24, then it makes little difference whether I use as a broadcast 255.255.255.255or 192.168.1.255.

But suppose now I am a member of the subnet 192.168.2.0/24, and I want to send a broadcast to all members of a different subnet, say, 192.168.1.0/24. How can I do that? I cannot use 255.255.255.255 because that is restricted to the LAN of the emitter, 192.168.2.0/24 in this example, and thus it will never reach 192.168.1.0/24 because routers drop these packets. But, aha, I can use 192.168.1.255 from outside 192.168.1.0/24 to reach all members of the network with a single broadcast, because the router separating my subnet, 192.168.2.0/24 from the target subnet, 192.168.1.0/24 will pass these packets on.

You may wonder when a proper use case for directed broadcasts is: the answer is, when you cannot use unicast. For instance, in Wake On LAN (WOL), I cannot send a unicast packet because the pc that must receive it is turned off, and thus has no IP address, so I must use a broadcast. But if I am doing this from outside the sleeping pc subnet, then I need to use a directed broadcast.

As you can see, both limited and directed broadcasts are quite useful, whether routers pass them along or not.
by Boss (25.6k points)
0
tell me difference b/w L.B.A and D.B.A  in terms of their application more clearly.

how L.B.A works and where????
0
lba for same network

dba for one network to different network
0 votes

"if NID=11.0.0.0  then a/c to definition of L.B.A we should write it as 11.255.255.255 "
 

No, LBA is reserved i.e. 255.255.255.255.
11.255.255.255 is DBA.

We all know broadcast address . It is the address used to address all in the same LAN ( Local Area network).
In broadcast we have two types : Limited broadcast and Directed broadcast. What is the difference between the directed broadcast and the Limited broadcast ?

Limited broadcast is the broadcast limited to a single LAN and which is to be received by all. It is sent to reserved Class E , IP address 255.255.255.255. The destination MAC address for such frames will be FF:FF:FF:FF:FF:FF.  The router simply drop the Limited broadcast address and does not forward it.


Directed Broadcast address is the local subnet broadcast address. If the subnet is 192.168.10.0 , the directed broadcast address will be 192.168.10.255 , which will be heard by all in the same subnet hosts. The router will receive such packet and process it.The  destination mac address will still be FF:FF:FF:FF:FF:FF, as it is to be received by all hosts.

DHCP packets are Limited broadcast packets and NBNS uses directed broadcast packets.
 

by Active (4k points)
0 votes
In DBA we put all 1 in host I'd part.

But in LBA we put all 1 throughout the address. Bcz it will not cross the router.

Ex: if IP address is 194.68.3.1

Then ,its belongs to class-c so last 8 bit is host I'd part .

DBA =194.68.3.255

LBA=255.255.255.255
by Junior (977 points)
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