Question:
computer networking ?
ian r
2008-11-13 08:03:16 UTC
does anyone know the answer to these? they are confsing the hell out of me
An Ethernet frame is as follows, where everything has been expressed in hexadecimal

aa aa aa aa aa aa aa ab ff ff ff ff ff ff 00 d0
2b 75 3d 8c 08 06 00 01 08 00 06 04 00 01 00 d0
2b 75 3d 8c 52 2d 78 01 00 00 00 00 00 00 52 2d
79 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

What is the destination MAC address of this frame?
What is the source MAC address of this frame?
Who would receive this message?
What is the IP address of the sender in dotted decimal notation?
Three answers:
Pablo
2008-11-13 10:31:30 UTC
This requires some time and work...



First, you need to know the Ethernet frame [1] and IP packet [2] formats, including the length, e.g. in bits, of each field. Now you need to match each field length with the corresponding hexadecimal values. Remember that each hexadecimal symbol represents four bits.



Wait! According to the pattern of hexadecimal values shown at first (aa aa aa ... ab), you should know that they -the first sixteen- represent the preamble + SFD, which only exist at the physical layer. In binary: 1010 1010 1010 ... 1011.



This is the result of matching fields with the information given:



[Ethernet frame header]

aa aa aa aa aa aa aa ab [Preamble (+ SFD) = 64 bits]

ff ff ff ff ff ff [Destination MAC address = 48 bits]

00 d0 2b 75 3d 8c [Source MAC address = 48 bits]

08 06 [Type/Length = 16 bits]





[Ethernet frame data]

[IP packet header]

0 [Version = 4 bits]

0 [IHL = 4 bits]

01 [Type of service = 8 bits]

08 00 [Total length = 16 bits]

06 04 [Identification = 16 bits]

00 01 [Flags + Fragment offset = 16 bits]

00 [TTL = 8 bits]

d0 [Protocol = 8 bits]

2b 75 [Header checksum = 16 bits]

3d 8c 52 2d [Source IP address = 32 bits]

78 01 00 00 [Destination IP address = 32 bits]

00 00 00 00 52 2d 79 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [The rest....]



Now that you have matched each field, let's answer the questions (Just see the result above):



1. What is the destination MAC address of this frame?

See the tag [Destination MAC address = 48 bits]...

ff ff ff ff ff ff = ff-ff-ff-ff-ff-ff As you can see, this is a broadcast address.



2. What is the source MAC address of this frame?

See the tag [Source MAC address = 48 bits]...

00 d0 2b 75 3d 8c = 00-d0-2b-75-3d-8c



3. Who would receive this message?

See the tag [Destination MAC address = 48 bits]...

All of the computers in the same broadcast domain, as the destination address is all-ones in binary (or ff ff ff ff ff ff in hexadecimal).



4. What is the IP address of the sender in dotted decimal notation?

See the tag [Source IP address = 32 bits]...

In hexadecimal: 3d 8c 52 2d

In dotted decimal notation: 61.140.82.45

It was an easy conversion. Just convert each pair of hexadecimal numbers to decimal: 3d (61) 8c (140) 52 (82) 2d (45)



It's done! See? It wasn't so difficult. ;-)
2008-11-13 08:05:56 UTC
Check out this forum, post your questions and get quick responses. And if you are interested in learning more about computers, or simply want to join a growing community, Why not register :)



http://www.yourpcforums.org
camel
2016-12-14 15:25:33 UTC
to establish your person wifi community, what's your router? it is your router that establishes your instantaneous community.. as quickly as set up, you have your person instantaneous community - user-friendly as that...


This content was originally posted on Y! Answers, a Q&A website that shut down in 2021.
Loading...