Hi all. I need some help with a BGP prefix list. A consulting group has
recommended the following prefix list in order to deny learning networks
that should not be learnt from the internet. I don't entirely trust these
guys to know what they are doing, so I would like to see what you all say
about this before I ask them specific questions.
For simplicity, the first part of each line -
ip prefix-list <word> seq <number> deny
has been left off. All of these lines are deny statements
0.0.0.0/32
0.0.0.0/8 le 32
0.0.0.0/1 ge 20
10.0.0.0/8 le 32
127.0.0.0/8 le 32
128.0.0.0/2 ge 17
128.0.0.0/16 le 32
172.16.0.0/12 le 32
192.0.2.0/24 le 32
192.0.0.0/24 le 32
192.168.0.0/16 le 32
191.255.0.0/16 le 32
192.0.0.0/3 ge 25
223.255.255.0/24 le 32
224.0.0.0/3 le 32
I've tried to work my way through this, and this is what I've got so far:
These I understand:
10.0.0.0/8 le 32 = 10.x.x.x (private 10 networks)
127.0.0.0/8 le 32 = 127.x.x.x (127 loopback addresses)
172.16.0.0/12 le 32 = 172.16.x.x-172.31.x.x (private 172 addresses)
192.168.0.0/16 le 32 = 192.168.x.x (private 192 addresses)
224.0.0.0/3 le 32 = 224.0.0.0-255.0.0.0 (class D & E addresses)
Are both of these statements necessary?
Doesn't the second one include the first?
0.0.0.0/32 = 0.0.0.0
0.0.0.0/8 le 32 = 0.x.x.x
I think I can understand this, I've heard that anything less then /19 is not
advertised across the internet. But, if that is true, what about the rest
of the networks?
0.0.0.0/1 ge 20 = 0.x.x.x thru 127.x.x.x, with mask /20 or more
Do these have somehthing to do with the above statement?
128.0.0.0/2 ge 17 = 128.x.x.x-191.x.x.x, with mask /17 or more
192.0.0.0/3 ge 25 = 192.x.x.x-223.x.x.x, with mask /25 or more
What the heck are these addresses?
128.0.0.0/16 le 32 = 128.0.x.x
192.0.2.0/24 le 32 = 192.0.2.x
192.0.0.0/24 le 32 = 192.0.0.x
191.255.0.0/16 le 32 = 191.255.x.x
223.255.255.0/24 le 32 = 223.255.255.x
Any help would be appreciated
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