ACL Placement Best Practices for Network Filtering
Access Control Lists (ACLs) are pivotal in network security and efficient traffic management. The best practices for the ideal placement of ACLs depends on the traffic direction and the intended purpose. Generally speaking, the rules of thumb are:
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Filtering Source Address: Place ACLs close to the source to mitigate unwanted traffic at the earliest possible point. This involves applying ACLs on each downstream link in an inbound direction.
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Filtering Destination Address: Apply ACLs close to the destination to control traffic leaving the network. For instance, traffic destined for the Internet should have ACLs applied in an outbound direction on the link to the ISP.
Because standard access lists filter only based on source traffic, such ACLs should adhere to the first rule.
Because extended access-lists filter based on both source and destination traffic, such ACLs can adhere to either rule of thumb, depending on the specific implementation.
These strategic placements help minimize unnecessary traffic flow, improve security, and optimize network performance. Understanding these best practices ensures a network is protected and efficiently managed.
Links
https://networklessons.com/security/standard-access-list-example-on-cisco-router
https://networklessons.com/security/extended-access-list-example-on-cisco-router