Can someone tell me how to create a Prefix-list to only alow classful routes
for BGP. I know you can do the following with an extended access-list:
access-list 100 permit ip 0.0.0.0 127.0.0.0 host 255.0.0.0
access-list 100 permit ip 128.0.0.0 63.255.0.0 host 255.255.0.0
access-list 100 permit ip
You can add prefixs with the command
ip prefix-list route/mask ge le
So,
ip prefix-list test deny 0.0.0.0/0 ge 8 le 24
This will deny all routes with a prefix between 8 and 24
You can also permit routes like 172.20.16.8/32
Or deny ranges and so on...CCO has stacks on BGP prefix lists..
Ho
I believe this will do what you are looking for. I did a little testing and
it seemed to work well:
ip prefix-list classful seq 5 permit 0.0.0.0/1 ge 8 le 8
ip prefix-list classful seq 10 permit 128.0.0.0/2 ge 16 le 16
ip prefix-list classful seq 15 permit 192.0.0.0/3 ge 24 le 24
Hope that helps
To better understand why this works:
In the very first octet, the following applies:
class A addresses start with the first bit = 0
class B addresses start with the first two bits = 10
class C addresses start with the first three bits = 110
So the 0.0.0.0/1 means look for a network address of
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