IP Standard ACL their Configuration Sequence Numbers and Wildcard Masks

IP Standard ACL their Configuration Sequence Numbers and Wildcard Masks

IP Standard Access Control Lists (ACLs) are used to filter traffic based on the source IP address only. They are numbered from 1 to 99 and 1300 to 1999.

The configuration of a standard ACL involves the following steps:

Enter global configuration mode:

configure terminal

Create the standard ACL using the access-list command followed by the ACL number and the permit or deny keyword. In this example, we will create ACL 10 to deny traffic from a specific source IP address:

access-list 10 deny host 192.168.1.10

(Optional) Add additional rules to the ACL using the same access-list command:

access-list 10 permit any

In this example, we added a rule to permit any traffic that is not denied by the previous rule.

Apply the ACL to an interface using the ip access-group command followed by the ACL number and the interface name:

interface GigabitEthernet0/0

 ip access-group 10 in

In this example, we applied ACL 10 to the incoming traffic on interface GigabitEthernet0/0.

Sequence numbers are used to reorder and add rules to the ACL. Wildcard masks are used to specify a range of IP addresses to match. The wildcard mask is the inverse of the subnet mask. For example, a subnet mask of 255.255.255.0 would have a wildcard mask of 0.0.0.255.

It’s important to note that standard ACLs should be applied as close to the source as possible, to avoid filtering traffic that has already traversed the network.

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