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access-list 1 permit 0.0.0.0

hilferns
Level 1
Level 1

Hi

What is the relevance of this command in the following context?

 

access-list 1 permit 0.0.0.0

!

interface g0/1

ip address 10.1.1.1 255.255.255.0

ip access-group 1 in

 

Thanks

3 Replies 3

InayathUlla Sharieff
Cisco Employee
Cisco Employee

Everything matching is allowed.


if you use access-list 1 permit 0.0.0.0
 
(if no mask defined then it will apply  Implicit Masks as 0.0.0.0 mask applied which means exact match only)

which means that this is acting like a matching of default route only. 

Thanks. So what does it really mean in terms of this access-list when you say matching a default route. This access list has been applied to an interface in the router. Does it mean that it will permit traffic from any source address?

 

Hilary

Eric Kang
Cisco Employee
Cisco Employee

Hilary,

When defining a standard access list and do not include a wildcard mask, you are specifying a particular host address. For example:

access-list 1 permit 192.168.10.10

will only permit traffic sourced from the 192.168.10.10 IP address.

Following the example above, unless you have a host with an IP of 0.0.0.0, the access list you're providing is essentially equivalent to:

access-list 1 deny any

If you would like an in-depth look on ACLs, please check out this Cisco doc on access lists:

http://www.cisco.com/c/en/us/support/docs/security/ios-firewall/23602-confaccesslists.html#standacl

and read the section titled Standard ACLs.

Regards,

Eric Kang