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Community Member

a simple question about access-list

my route has following configuration:

access-list 1 permit 0.0.0.0

access-list 1 permit 131.108.0.0 0.0.15.255

access-list 1 deny 1.1.0.0 255.255.255.255

I can't understand what's mean of these.

my question is :

1.access-list 1 permit 0.0.0.0 permit what range of ip address.

2.access-list 1 permit 131.108.0.0 0.0.15.255 permit what range of ip address.

thank you!

3 REPLIES
Community Member

Re: a simple question about access-list

permit 0.0.0.0 has no mask, so it permits just that: 0.0.0.0 (0.0.0.0 to 0.0.0.0 is the range)

(permit 0.0.0.0 is equivalent to permit 0.0.0.0 0.0.0.0 - all bits must match to pass.)

Note that you would only use 0.0.0.0 for filtering routes, not traffic, because the range only includes the default which would only be used as a route, never as a source or destination address in a packet.

permit 131.108.0.0 0.0.15.255 has a wild card mask ("don't care" bits) which can be analyzed in binary:

00000000.00000000.00001111.11111111

10000011.01101110.00000000.00000000

This indicates a range of:

10000011.01101110.00000000.00000000 to 10000011.01101110.00001111.11111111

which translates into decimal:

131.108.0.0 to 131.108.15.255

It would be a little more complicated to visualize if you had a subnet like this:

permit 131.108.48.0 0.0.15.255

Again in binary:

00000000.00000000.00001111.11111111

10000011.01101110.00110000.00000000

This indicates a range of:

10000011.01101110.00110000.00000000 to 10000011.01101110.00111111.11111111

which translates to decimal:

131.108.48.0 - 131.108.63.255

Hope this helps,

Mark

Community Member

Re: a simple question about access-list

Thank for your reply.It solved my question.

Community Member

Re: a simple question about access-list

I hate to disagree with you but 0.0.0.0 is used as a source address when a PC sends out a DHCP request. The source address is 0.0.0.0 and the destination is 255.255.255.255. I agree with everything else though.

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