From: Raj Bahad (raj.bahad@xxxxxxxxxxxxxx)
Date: Wed Jul 17 2002 - 16:18:43 GMT-3
Hi all,
I think I've got my head around filtering a range of subnets using
access-lists.
However, just for clarification, lets say i am asked to allow only even
subnets through with a value which is divisible by 2, would it be:
access-list 1 permit 192.168.10.0 0.0.0.254
where 254 = 11111110 which means ignore the first 7 bits of the last octet
and
match on the eighth. In this case, because the eighth bit is equal to
decimal
1 (plus the 0), this would indeed permit hosts 0,2,4,6,8...
If the above statement is correct, then 192.168.0.255 0.0.252.255 would
permit
all even subnets which are divisable by a value of four i.e. 0,4,8,12,16...
with all hosts in the 4th octet.
Finally if i want to specify a filter which permits even subnets but odd
hosts
(both of which are divisable by 2), then would the following example satisfy
this request.
access-list 2 permit 192.168.0.1 0.0.254.254
My theory for the above example is based on the 3rd octet filtering on even
subnets due to the respective 3rd octet of the network address being 0 and
the
4th octet will permit odd numbers (1,3,5,,7,9...) because the 4th octet of
the
network address has a value of 1.
Your expertise will be appreciated.
Thanks,
Raj.
--- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.375 / Virus Database: 210 - Release Date: 10/07/2002
This archive was generated by hypermail 2.1.4 : Sat Sep 07 2002 - 19:36:34 GMT-3