From: Paresh Khatri (Paresh.Khatri@aapt.com.au)
Date: Tue Jun 28 2005 - 19:45:55 GMT-3
Hi Guys,
As Chris rightly mentioned, the first byte is the AFI. The AFI is specified in BCD (binary coded decimal) format so you cannot have an AFI value of FF. The highest AFI value that you can have is 99 (which would be coded in binary as 10011001).
Hope that helps.
Paresh.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Chris Lewis (chrlewis)
Sent: Wednesday, 29 June 2005 02:09 AM
To: san; lab
Subject: RE: ISIS Networks
Ahh, I understand what you are getting at now.
As long as the system ID is 6 bytes, both ff.systemid.00 and
00.00ff.systemid.00 are valid, it just depends how long the overall
address has to be, depending on question requirements. The area ID has
to be between 1 and 13 bytes in length. However, be careful, the first
byte in the area ID can have special meaning, and is known as the AFI,
specifying a top-level ISO addressing authority. In a private network,
this should not matter though and the common practice is to set the AFI
to the value 49, which is private addressing for NSAPs.
Chris
-----Original Message-----
From: san [mailto:san.study@gmail.com]
Sent: Tuesday, June 28, 2005 10:02 AM
To: Chris Lewis (chrlewis); lab
Subject: Re: ISIS Networks
Chris,
Can you explain, why
ff.systemid.00 cannot be used at ISIS net while converting "255"
decimal to hex .
I would like to know the reason about prefix "00.00" for
"ff.systemid.00". whether its a compulsary prefix to be attached ?
/SAN
On 6/28/05, Chris Lewis (chrlewis) <chrlewis@cisco.com> wrote:
> San,
>
> I don't quite understand what you are saying.
>
> It is safe to assume that anything given to you in the formate
> 49.0255.x.x.x.00 is already in hex.
>
> It is also safe to assume that if you are told in the question, an
> area has to have a value, say 255, it must be converted in to hex
> before being used in the NET value.
>
> The only significance to the number of x's in my post was that each
> value between the periods will have 4 characters.
>
> The key issue is that the six bytes before the n-selctor are the
> system ID, anything before that is the system ID, so in the example
> you give the area ID will be 00.00ff.x assuming that in your case x
> represents the two byte value that is inserted between periods in the
> NET value format.
>
> Chris
>
> -----Original Message-----
> From: san [mailto:san.study@gmail.com]
> Sent: Monday, June 27, 2005 9:03 PM
> To: Chris Lewis (chrlewis)
> Cc: ccie2be; Lee Carter; CCIE LAB
> Subject: Re: ISIS Networks
>
> Chris,
>
> net 49.0255.x.x.x.x.00 if its given in hex & equivalent area id in
> decimal will be a huge number correct ?
>
> For the above question (255 in decimal to net value )
> ff.x.x.x.x.00 => is wrong value ? No assumptions of Zero at begining
> is it ??
>
> 00.00ff.x.x.x.x.00 => is the correct value !!
>
> /SAN
>
>
> On 6/27/05, Chris Lewis (chrlewis) <chrlewis@cisco.com> wrote:
> > One last point, consider the format of the NET.
> >
> > The NET can be 8-20 bytes, with the last byte set to zero. The 6
> > bytes
>
> > directly in front of this last byte are the system ID. All bytes in
> > front of the system ID are the area ID. So if you are given 255 in
> > decimal as the area ID, look at it like this:
> >
> > 00.00FF.xxxx.xxxx.xxxx.00
> > Area ID.System ID .N-selector and must be 0
> >
> > Chris
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > Of ccie2be
> > Sent: Monday, June 27, 2005 5:12 PM
> > To: 'Lee Carter'; 'CCIE LAB'
> > Subject: RE: ISIS Networks
> >
> > Lee,
> >
> > As long as you remember that the NET is in HEX, you should be fine.
> > In all likelihood, the task will be worded in such a way there won't
> > be any ambiguity.
> >
> > However, if you're unsure, ALWAYS ask the proctor.
> >
> > Tim
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > Of Lee Carter
> > Sent: Monday, June 27, 2005 5:50 PM
> > To: CCIE LAB
> > Subject: ISIS Networks
> >
> > All,
> >
> > Ok, so when defining isis net's I have seen two different solutions
> > where they say.. Put a particual isis network in say net 255 to keep
> > it easy.
> >
> > One solution would use:
> >
> > net 49.0255.xxxx.xxxx.xxxx.00
> >
> > The other (which I believe is correct) would use:
> >
> > FF.0000.xxxx.xxxx.xxxx.00
> >
> > Since the firt two bits are in HEX.
> >
> > Thoughts?
> >
> >
> >
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