From: Nigel.Johnson@barclayscapital.com
Date: Thu Apr 01 2004 - 02:59:25 GMT-3
Assume the following scenario:
Router1 is sending Router2 the following networks (routing protocol not
important):
192.168.1.0 /24
172.16.16.0 /24
I now want to only allow the 192.168.1.0 /24 route into Router2. So, I can
do this with a distribute list as follows:
access-list 1 permit 192.168.1.0 0.0.0.255
distribute-list 1 in serial 0
This works fine. However, this distribute list would also allow any subnets
of 192.168.1.0 /24. e.g 192.168.1.32 /27
If I just wanted to allow 192.168.1.0/24 then I would change my access list
to:
access-list 1 permit host 192.168.1.0
So 'Whats your point?' I hear you ask. We'll in the R&S lab, if the question
wants us to filter a route should we use:
(1) My first access list
(2) My seconds access list, or
(3) Either are ok
Obviously if the question is very specific and states that ONLY the major
network 192.168.1.0/24 is to be allowed and no subnets then we would opt for
the second.
The reason I bring this up is because I'm working through the IPEXPERT
workbook and have always used my second style of access list when filtering,
whereas the solutions use the the first, more 'loose' access list.
Thanks
Nigel
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