Basic TCP/IP and Networking

Ohhh...

Thanks for taking the time to write this.

UDP -- The User Datagram Protocol (UDP) is in the same OSI layer as TCP. UDP is more used for simple data transfers.

UDP Header

16 bits
<------------------>
8 bits
<------->

+--------------------+--------------------+
| source port | destination port |
+--------------------+--------------------+
| length | checksum |
+--------------------+--------------------+

The (network) protocol IP from OSI layer 3 is only responsible for transporting packets from one to another. Both transport protocols TCP and UDP have to make sure that the packets are received by the right computer. To arrange this, UDP and TCP are using ports for addressing. A port is a 16 bits number. A not standard application which uses UDP or TCP can use different ports on both sides of the communication line or choose a port which is free. (portnumbers from 0 to 255 have a special meaning because some of them are standard we call them "well known ports", ports which have the number 256 and above are used for different applications which are not standard.

Wow!!! how great this is men !@!!!

thanks for the tut ;its a really good one and written in a nice way

A belated reply but I had to post something about:

Quote:

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Originally Posted by Arcanus Aegis

Another addition:

UDP, being broadcasted, does not pass through routers since routers do not pass broadcast traffic. This is why UDP will only be found small, internal networks, and TCP, even with it's slightly greater overhead, is much more common.

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Wow...I continued reading the thread after I read this...and I am still laughing now!

Could someone tell me how my UDP DNS lookups get off my small internal network, past two routers, two firewalls, out on to the internet, past countless other backbone routers, find a DNS server and come all the way back on to my small internal network.....and at the same time have a destination address of my subnets broadcast address as it has to be a broadcast packet because it is UDP......cause I am mighty confused now! :D

I didn't see a mention of TCP Sequence numbers on the original explanation, which are just as important as the TCP flags - if not more so.

This is NOT a plug for myself or the site but as there seems to be some genuine interest in this subject, there are some slightly more advanced TCP/OSI/Routing etc tutorials HERE HERE and HERE

Quote:

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It also makes sure that all packets get there in the same order that they were sent.

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Quote:

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Originally Posted by Nokia

I didn't see a mention of TCP Sequence numbers on the original explanation, which are just as important as the TCP flags - if not more so.

This is NOT a plug for my

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hehehe.. I thought the same thing Nokia. When I saw the first quote that I put into this reply I laughed pretty hard. TCP doesn't care what order the packets arrive in because it can put them back into the proper order. So to say that TCP makes sure that all apckets get there in the same order that they were sent is completely wrong.

You need to implement some type of Quality Of Service(QOS) on top of tcp/ip for packets that absolutely have to arrive in the proper order. The best example of this is VOIP or internet based TV.