From: Jonathan V Hays (jhays@jtan.com)
Date: Thu Nov 13 2003 - 11:02:03 GMT-3
from Doyle, Volume II, Page 278:
set community 400:50
set community 0x1900032
set community 26214450
All these commands specify a 32-bit number in which the first 16 bits is
400 in decimal and the second 16 bits is 50 in decimal.
---So the basic problem is how to convert each of these to binary. Using the Windows scientific calculator (which is what you have available on the CCIE Lab exam):
400:50 in binary 110010000:110010 adding the leading zeros to give 32 bits 0000000110010000:0000000000110010 and removing the colon divider 00000001100100000000000000110010
0x1900032 in binary if you know your hex digits you can just type them out 0001 1001 0000 0000 0000 0011 0010 remove the spaces between the hex digits 0001100100000000000000110010 add leading zeros to give 32 bits 00000001100100000000000000110010 26214450 in binary (direct conversion from decimal to binary) 1100100000000000000110010 adding leading zeros to give 32 bits 00000001100100000000000000110010
You can copy and paste the results of each of the three calculations underneath each other to verify they are the same. Converting in the opposite direction is just a matter of dividing the 32-bit binary number up into groups of 4 hex digits or two 16 bit halves on each side of the colon.
Now, for the sake of thoroughness, let's take your example.
100:2000 in binary 1100100:11111010000 add leading zeros to give 32 bits 0000000001100100:0000011111010000 remove the colon 00000000011001000000011111010000
0x6407d0 in binary 0110 0100 0000 0111 1101 0000 remove the spaces between the hex digits (or you could just type the hex digits into the calculator and convert) 011001000000011111010000 add leading zeros to give 32 bits 00000000011001000000011111010000
6555600 in binary 11001000000011111010000 add leading zeros to give 32 bits 00000000011001000000011111010000
Copy and paste all three results below each other and you will see they are the same.
HTH,
Jonathan
-----Original Message----- From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of JamesGEF Sent: Thursday, November 13, 2003 8:24 AM To: ccielab@groupstudy.com 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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