[Day 10] 2. Standard ACL

A Standard ACL filters traffic based solely on the source IP address, allowing or blocking traffic based on whether it matches a specified address.

Commands:

```
A(config)# access-list 10 permit 172.16.10.10 0.0.0.0
```
:
This command allows traffic from the exact IP address
```
172.16.10.10
```
. The wildcard mask
```
0.0.0.0
```
ensures that only this specific IP address is allowed.
```
A(config-if)# ip access-group 10 in
```
and
```
A(config-if)# ip access-group 10 out
```
:
These commands apply ACL 10 to the interface, controlling whether traffic coming into or going out of the interface is filtered.

Example: Blocking Specific IP Address

To prevent the device with IP address

172.16.10.10

from communicating, while allowing all other devices, the following commands can be used:

```
A(config)# access-list 10 deny 172.16.10.10 0.0.0.0
```
:
This denies traffic from the specific host
```
172.16.10.10
```
. You can also use
```
host 172.16.10.10
```
instead of
```
172.16.10.10 0.0.0.0
```
to achieve the same result.
```
A(config)# access-list 10 permit 0.0.0.0 255.255.255.255
```
:
This command allows all other traffic. You can use
```
any
```
in place of
```
0.0.0.0 255.255.255.255
```
for simplicity.
```
A(config)# int g0/0
```
:
Enter the interface configuration mode for the specific interface (e.g.,
```
g0/0
```
).
```
A(config-if)# ip access-group 10 in
```
:
Apply ACL 10 to filter incoming traffic.

Important Note:

The permit command is necessary to ensure other traffic is allowed. Without the
```
permit
```
command, only denied traffic will be filtered, and no other traffic will be permitted.
The order of the commands is critical. If the
```
permit
```
command is placed after the
```
deny
```
command, it ensures all traffic except
```
172.16.10.10
```
is allowed. Reversing the order would result in
```
172.16.10.10
```
being allowed due to the broader
```
permit
```
rule.

[Day 10] 2. Standard ACL

Example: Blocking Specific IP Address

Read Next

[Day 10] 3. Golden Rules of ACL

[Day 10] 4. Extended ACL