Do VLANs with no ACL assigned block inter-VLAN traffic by default?

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VLANs are an important part of any network infrastructure, allowing networks to be logically segmented for better security and performance. But one of the most common questions about VLANs is whether they block inter-VLAN traffic by default. The answer is that it depends on the configuration of the VLANs.

When VLANs are configured with no ACL assigned, traffic is not blocked by default. Without an Access Control List (ACL) configured, the switch will not inspect or filter any traffic entering or leaving the VLAN. This means that any device connected to the VLAN can communicate with any other device on the same VLAN regardless of the source or destination IP address.

However, it is important to note that without an ACL, the switch will not be able to differentiate between different types of traffic. This means that all traffic, including potentially malicious traffic, will be allowed to pass through the VLAN. As such, it is important to configure an ACL if you wish to impose restrictions on the traffic allowed through the VLAN.

When an ACL is configured, it is possible to block traffic between VLANs. This is done by creating rules specifying which traffic is allowed and which is blocked. For example, you could create a rule that blocks all traffic from one VLAN to another. This would effectively block any communication between the two VLANs.

While it is possible to block traffic between VLANs with an ACL, it is important to remember that there is also the possibility of creating a security hole by allowing traffic that should be blocked. As such, it is important to carefully consider the rules you create when configuring an ACL.

In general, it is best practice to configure an ACL on VLANs to ensure that unwanted traffic is blocked. Without an ACL, any traffic can pass through the VLAN, including potentially malicious traffic. An ACL will allow you to control which traffic is allowed and which is blocked, providing an additional layer of security.

To summarise, VLANs do not block inter-VLAN traffic by default. Without an ACL, any traffic can pass through the VLAN. An ACL can be configured to block certain types of traffic, providing an additional layer of security. In general, it is best practice to configure an ACL on VLANs to ensure that unwanted traffic is blocked.

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