| Author |
CCNA Question. Don't have an answer
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| mindmesh 2003-08-07, 4:33 pm |
| Which portion of the TCP header provides a connection to the upper-layer protocol?
a. destination port
b. sequence number
c. protocol number
d. DSAP
I don't have the answer. Wondering if anyone does.. | |
| kokonaing 2003-08-07, 10:58 pm |
| I guess the destination port might be the one that can communicate with the upper layer protocols. It's multiplexing property of Transport Layer..
Ko Ko | |
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| hello there,
i think the answer is destination port alright. but i'm having trouble about the DSAP and protocol number. where in TCP header do they reside? the source port is a random comm. port but the destination port always signifies a service running on the destination computer, like port number 53 for DNS. | |
| jason892 2003-08-08, 8:12 am |
| From what I can gather, the DSAP is primarily used in token ring and FDDI networks. If the transmission protocol being used uses csma/cd, then there will be no DSAP field. With that being said, a tcp packet may traverse several different segments on it's journey where it goes through different transmission protocols. Each time it changes, the DSAP is either added or removed. That tells me that it wouldn't provide a service to an upper layer protocol. It seems to me that would almost have to be a layer 2 or maybe a layer 3 service. I would have to go with the destination port for the answer to that question. I found this, if it helps any:
http://developer.novell.com/researc...tembe/05/02.htm | |
| SureshHomepage 2003-08-09, 12:52 am |
| Hi all,
the answer would be little bit tricky. The question asked here talks about fields inside the TCP header.
Protocol number is something that is NOT part of TCP header but the IP header. On the IP header it is referred by the name 'protocol'.
For example, the network software puts the UDP header on the front of your data just as it would put a TCP header on the front of your data. Then UDP sends the data to IP which adds the IP header putting UDP's protocol number in the protocol field instead of TCP's protocol number.
Source Port When you are sending a datagram the sending PCs TCP port becomes the "source" port since you are the source of the datagram.
Destination Port is one on the other side of the PC which would receive the datagrams you sent. Upon receiving it will send it to the upper layer protocols.
So the answer for this question is Destination Port. |
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