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If I enter for example "block 59.164.0.0/20" as a firewall rule.

Does that mean it blocks the IPs 59.164.0.0 to 59.164.0.20 or does it mean something else ?

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3 Answers 3

up vote 7 down vote accepted

This is in CIDR notation (Classless Inter Domain Routing).

59.164.0.0/20

is the same as

59.164.0.0 to 59.164.15.255

In reality though, you will only be able to use 59.164.0.1 to 59.164.15.254 for assigning to hosts.

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no. /20 is the netmask, not part of the ip address. /20 is the same as 255.255.240.0 and refers to 4096 addresses, not 20.

http://en.wikipedia.org/wiki/CIDR_notation

http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing

http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing#Prefix_aggregation

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If that's a block rule on your firewall it means it will block traffic from the ip address range 59.164.0.0 through 59.164.15.255, inbound or outbound depending on the rule's disposition (inbound or outbound traffic\service rule).

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