I'm currently studying to get my CCNA. I have some background
in networking, but not enough to make any sense, so I figured I'd
start from the beginning. I read a part in the book about the hex
coversions. From Hex to binary and decimal, and back. I can figure
out the binary and decimal part, that's pretty easy for me. What I
can't figure out, is how hex gets shortened to 4 numbers, 3 segments
in the cisco book i have, and how to do that. Any would be
great!

Thanks,

Outta Luck wrote:

> I'm currently studying to get my CCNA. I have some background
> in networking, but not enough to make any sense, so I figured I'd
> start from the beginning. I read a part in the book about the hex
> coversions. From Hex to binary and decimal, and back. I can figure
> out the binary and decimal part, that's pretty easy for me. What I
> can't figure out, is how hex gets shortened to 4 numbers, 3 segments
> in the cisco book i have, and how to do that. Any would be
> great!

What the heck are you talking about? What does "hex gets shortened to 4
numbers" mean? What do you mean by "segments"?

If you can understand binary, you can understand hex. To convert hex to
binary, just replace hex digits with binary bits as follows:

0 = 0000 1 = 0001 2 = 0010 3 = 0011
4 = 0100 5 = 0101 6 = 0110 7 = 0111
8 = 1000 9 = 1001 A=1010 B=1011
C=1100 D=1101 E=1110 F=1111

To convert binary to hex, just add zeroes onto the beginning until you
have a multiple of four bits, then replace groups of 4 bits with
0-9,A-F from the table above.

DS

The book I'm studying is Cisco Networking Basics. It says something about
router configuration registry, about converting to hex. Then it points me
to some table saying the hex number, then the decimal, then the binary.
After that, it comes up with addresses looking like "0x2102" and
"0200.2222.2222" What I'm trying to figure out is how they come up with
these #'s from the hex code. All I've ever seen is hex code in the way
MAC addresses are, like "c4:34:54:23:ae:ce" and the like. Sorry if I
confused you, I'm kind of brand new to this, and have no clue what I'm
looking at.

On Tue, 24 Oct 2006 05:25:22 -0700, David Schwartz wrote:


> What the heck are you talking about? What does "hex gets shortened to 4
> numbers" mean? What do you mean by "segments"?
>
> If you can understand binary, you can understand hex. To convert hex to
> binary, just replace hex digits with binary bits as follows:
>
> 0 = 0000 1 = 0001 2 = 0010 3 = 0011
> 4 = 0100 5 = 0101 6 = 0110 7 = 0111
> 8 = 1000 9 = 1001 A=1010 B=1011
> C=1100 D=1101 E=1110 F=1111
>
> To convert binary to hex, just add zeroes onto the beginning until you
> have a multiple of four bits, then replace groups of 4 bits with
> 0-9,A-F from the table above.
>
> DS

Outta Luck wrote:

> The book I'm studying is Cisco Networking Basics.

Sorry, I don't have that book.

> It says something about
> router configuration registry, about converting to hex. Then it points me
> to some table saying the hex number, then the decimal, then the binary.

Okay.

> After that, it comes up with addresses looking like "0x2102" and

Prefixing a number with '0x' is a common way to indicate hexadecimal.
(It's C-style notation.)

> "0200.2222.2222"

Prefixing a number of '0' is a common way to indicate octal. This is
also C-style notation. Octal converts to binary using groups of three
bits just as hexadecimal does with groups fo four bits. (2^4=16 2^3=8)

In this case though, I think this is a MAC adress in hexadecimal being
placed in groups of four digits separated by dots rather than the more
common representation. This is a common example MAC address in Cisco
examples, which is kind of strange since it's not a realistic-looking
MAC address.

> What I'm trying to figure out is how they come up with
> these #'s from the hex code. All I've ever seen is hex code in the way
> MAC addresses are, like "c4:34:54:23:ae:ce" and the like.

MAC addresses are typically blocked into 8-bit sections separated by
colons (or less commonly, hyphens) with their values expressed in
hexadecimal. This is more common than groups of four separated by dots.
The great thing about standards is that there are so many to choose
from.

> Sorry if I
> confused you, I'm kind of brand new to this, and have no clue what I'm
> looking at.

If they had put C434.5423.AECE (or any realistic-looking MAC address),
I think it would have been clearer.

That makes sense. So I was looking at everything the way I should be,
just in a different format, that didn't make any sense. Thanks DS for the
explanation, invaluable.

Outta Luck


On Tue, 24 Oct 2006 08:34:49 -0700, David Schwartz wrote:

>
> Outta Luck wrote:
>
>> The book I'm studying is Cisco Networking Basics.
>
> Sorry, I don't have that book.
>
>> It says something about
>> router configuration registry, about converting to hex. Then it points me
>> to some table saying the hex number, then the decimal, then the binary.
>
> Okay.
>
>> After that, it comes up with addresses looking like "0x2102" and
>
> Prefixing a number with '0x' is a common way to indicate hexadecimal.
> (It's C-style notation.)
>
>> "0200.2222.2222"
>
> Prefixing a number of '0' is a common way to indicate octal. This is
> also C-style notation. Octal converts to binary using groups of three
> bits just as hexadecimal does with groups fo four bits. (2^4=16 2^3=8)
>
> In this case though, I think this is a MAC adress in hexadecimal being
> placed in groups of four digits separated by dots rather than the more
> common representation. This is a common example MAC address in Cisco
> examples, which is kind of strange since it's not a realistic-looking
> MAC address.
>
>> What I'm trying to figure out is how they come up with
>> these #'s from the hex code. All I've ever seen is hex code in the way
>> MAC addresses are, like "c4:34:54:23:ae:ce" and the like.
>
> MAC addresses are typically blocked into 8-bit sections separated by
> colons (or less commonly, hyphens) with their values expressed in
> hexadecimal. This is more common than groups of four separated by dots.
> The great thing about standards is that there are so many to choose
> from.
>
>> Sorry if I
>> confused you, I'm kind of brand new to this, and have no clue what I'm
>> looking at.
>
> If they had put C434.5423.AECE (or any realistic-looking MAC address),
> I think it would have been clearer.