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RE: BGP Communities posted 11/13/2003
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I understand the process, and will show you, but I don't understand the
value represented.  :)  

Binary....  It's all just a series of bits.

100 = 1100100 in binary
2000 = 0000011111010000 in binary  (16-bit minimum field length)

Together they make 1100100 0000011111010000 which is 6555600 in decimal
or 0x6407d0.

>From what I've seen in postings (and RFC2547 if I remember right), there
are two typical formats for coming up with an RD.  Either your
AS-number(16 bit):any-number(32-bit) or any-number(IP
format)(32-bit):any-number(16-bit).

This translates to:

ASN:random(32-bit)
IP-address:random(16-bit)

So with that in mind, somehow, someone is assuming that 100 is an IP
address value, which seems a little odd. Thinking in the ASN format, the
value you would get would be 1100100 00000000000000000000011111010000,
which is 429496731600 in decimal or 0x64000007D0 in hex.  *shrug*

 
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
CISSP, JNCIS, et al.
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
swm@xxxxxxxxxx/smorris@xxxxxxxxxxxx
http://www.ipexpert.net


-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of
JamesGEF
Sent: Thursday, November 13, 2003 8:24 AM
To: ccielab@xxxxxxxxxxxxxx
Subject: BGP Communities


I'm doing some exercises in Doyle's book on BGP.  In regards to
communities, I don't see how to calculate community values from the
AA:NN format to decimal or binary.

For example, the AA:NN value is 100:2000.  How does it calculate 6555600
as the decimal value and 0x6407d0 as its hex value?

James

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