3)but some guys dun understand what does it mean router? .. Router or
gateway is a hardware device that fowards packets from one physical network
to another [i said from network to another not from a PC to another in the
same LAN, cause Router dun forward packets from two PCs in one LAN ,i
explained this above]. your PC or your IP uses a routing table to determine
which networks that packets can be forwarded to.. and Routers will only
forward packets to networks that it has been configured to do so. When a
packet is being sent, your computer or more specifically your IP determines
whether or not the IP address is local or remote. If it is local, it forward
the packet. If it is remote, it checks the routing table to determine the
path to the remote host. If there is no entry in the routing table, then the
default gateway [router] is used to do this jop. The router check its
routing table and the process repeats,will the router be able to forward
this packet from the source computer to the distination?if not it will send
a broadcast to the next router and so on.. router to router and router to
router..Each one of these steps is called a "hop". If a route to the remote
host is never found then an error message will return. So if you want to see
what i mean .. make a tracert in your MS-DOS or traceroute on your unix
shell and you will see
something like this:
c:\>tracert 127.0.0.1 [this is localhost.. i mean your IP when u r online or
offline .. so when you ping 127.0.0.1 .. you ping your PC]
Tracing route to 127.0.0.1 over a maximum of 30 hops
This syntax tell you that the tracing process will be for 30 hop only .. so
if you a trace a packet to the distnation computer and this packet passes
through more than 30 router ,the process will be trminated or "Destination
Unreachable" error will appear ..
To our main Point "how to send broadcast message"
4)IP addresses can be class A, B or C. Class A addresses are for networks
with a huge number of hosts. The first numbers is the NETid like 62.0.0.0
[here in Egypt , for NileOnLine ISP] and the 3 remaining are the HOSTid
,Example .. IPs for "Link.net" [a big ISP here in Egypt] will start as
62.1.0.0 to 62.253.x.x [cause 0 and 254 and 255 is reserved] Understood now?
. Class B addresses are used in medium to large networks with the first 2
parts [the NETid],Example .. if egyptnetwork.com give some IPs to cyber like
connect or goal [famous cybers in egypt] the IP in the cyber will be
62[NETid].139[HOSTid for "link.net" and NETid for "egyptnetwork.com"] and
the remaining 2 are the hostid fot "egyptnetwork.com".Class C is for smaller
networks with the first 3 parts are the netid and the last part is the
hostid, example 62[NETid for "link.net"].139[The NETid for
"egyptnetwork.com" and HOSTid for "link.net"].52[HOSTid for
"egyptnetwork.com" and NETid for the cyber].252[HOSTid for the cyber] .. i
know this is very complex but relax and read again and again ,You will find
it easy :) And That is for now .. thanx
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