08-28-2008 08:15 AM - edited 03-03-2019 11:18 PM
Hi Master,
I quite confuse with the values behind the ip prefix list. Can some1 make me understood ?
For example :
ip prefix-list A permit 10.18.0.0/21 ge 24 le 24
08-28-2008 11:07 AM
Hello William,
the prefix-list means:
permit all prefixes within 10.18.0.0/21 address block if their prefix-length is Greater equal 24 and less equal 24 ==>
all prefixes within 10.18.0.0/21 with prefix length = 24
10.18.1.0/24 is permitted
10.18.2.128/25 is denied
10.18.4.0/23 is denied
if present are permitted:
10.18.0.0/24
10.18.1.0/24
10.18.2.0/24
10.18.3.0/24
10.18.4.0/24
10.18.5.0/24
10.18.6.0/24
10.18.7.0/24
/21 means 3 bit of third byte
Hope to help
Giuseppe
08-28-2008 06:55 PM
Hi Giuseppe, thanks for ur answer.
some confusion on the /21. Is this mean ? :
128 64 32 16 8 4 2 1
--------------------
0 0 0 0 0 1 1 1
/21 means it allow :
10.18.0.0-10.18.11.0 (Correct me if i'm wrong)
* As for the Greater equal 24 and less equal 24 is only match the mask is it ?
So the answer for this is it only allow 10.18.0.0-10.18.11.0 with the mask of /24 only.
CORRECT ME IF WRONG. thanks !! in learning curve :-)
08-28-2008 11:33 PM
Hello William,
when we think of network mask we think of binary digits:
/21 moves 3 bits to the left the net boundary
so with 3 binary digits you can address
000 - 111 but 111 binary = 7 decimal
we use the dotted decimal notation as an help for us human beings but IP addresses are 32 bits numbers.
exercise yourself in binary and only later convert in decimal at each octet / byte boundary.
No problem to be in the learning curve : all of us are in the learning curve
Hope to help
Giuseppe
04-05-2017 10:23 PM
no comments
05-17-2018 12:42 AM
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