Cisco: prevent vlan's of communicating with eachother on cisco router (ACL alternative)



### Cisco Prevent VLANs of Communicating With Each Other on Cisco Router ACL

As an IT administrator, it is important to maintain secure network communication between network segments. As networks become larger, it is increasingly important to secure communication between virtual local area networks (VLANs) and ensure that each VLAN is secured from unauthorized access. In order to achieve this, IT administrators can apply access control lists (ACLs) to the routers of a network. This article will discuss how to use Cisco router ACLs to prevent VLANs from communicating with each other.

An access control list (ACL) is a set of rules that defines what type of network traffic is allowed or denied based on criteria such as source and destination IP address, source and destination port numbers, and more. ACLs are used to control access to various resources, such as networks, subnets, and individual hosts. To use ACLs on a Cisco router, the administrator must define an access list (ACL) and then apply the list to the router.

When using ACLs to secure communication between VLANs, the administrator must first create an ACL that denies all traffic from one VLAN to another. This can be done by using the `deny` command in Cisco IOS. The administrator should specify the source and destination VLANs in the ACL. For example, the following command denies all traffic from VLAN 10 to VLAN 20:

`deny ip any any vlan 10 vlan 20`

Once the ACL is created, it must be applied to the router. This can be done by using the `interface` command in Cisco IOS. For example, the following command applies the ACL to the router's interface connecting to VLAN 10:

`interface vlan 10`

`ip access-group ACL-VLAN10-20 in`

The `in` parameter specifies that the ACL should be applied to incoming traffic to VLAN 10. Once the ACL is applied, any traffic from VLAN 10 to VLAN 20 will be denied.

It is also possible to limit communication between VLANs by using the `ip route` command in Cisco IOS. This command can be used to specify which VLANs are allowed to communicate with each other. For example, the following command allows only VLANs 10 and 20 to communicate with each other:

`ip route 10.0.0.0 255.255.255.0 10.0.20.0 255.255.255.0 vlan 10 vlan 20`

The `vlan` parameter specifies which VLANs are allowed to communicate with each other. In this example, only traffic from VLAN 10 to VLAN 20 is allowed.

In summary, it is possible to secure communication between VLANs by using access control lists (ACLs) on Cisco routers. ACLs can be used to deny traffic between VLANs, while the `ip route` command can be used to limit which VLANs can communicate with each other. By using these tools, IT administrators can ensure that each VLAN is secure and that communication between VLANs is limited to authorized traffic.

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