Cabletron Systems 9032578-05 manual Using ACLs, Applying ACLs to Interfaces

Chapter 19: Access Control List Configuration Guide

If you edit and save changes to an ACL that is currently being used or applied to an interface, the changes will take effect immediately. There is no need to remove the ACL from the interface before making changes and reapply it after changes are made. The process is automatic.

Using ACLs

It is important to understand that an ACL is simply a definition of packet characteristics specified in a set of rules. An ACL must be enabled in one of the following ways:

•Applying an ACL to an interface, which permits or denies traffic to or from the SSR. ACLs used in this way are known as Interface ACLs.

•Applying an ACL to a service, which permits or denies access to system services provided by the SSR. ACLs used in this way are known as Service ACLs.

•Applying an ACL to ports operating in Layer-4 bridging mode, which permits or denies bridged traffic. ACLs used in this way are known as Layer-4 Bridging ACLs.

•Associating an ACL with ip-policy,nat, port mirroring, rate-limit, or web-cache commands, which specifies the criteria that packets, addresses, or flows must meet in order to be relevant to these SSR features. ACLs used in this way are known as Profile ACLs.

These uses of ACLs are described in the following sections.

Applying ACLs to Interfaces

An ACL can be applied to an interface to examine either inbound or outbound traffic. Inbound traffic is traffic coming into the SSR. Outbound traffic is traffic going out of the SSR. For each interface, only one ACL can be applied for the same protocol in the same direction. For example, you cannot apply two or more IP ACLs to the same interface in the inbound direction. You can apply two ACLs to the same interface if one is for inbound traffic and one is for outbound traffic, but not in the same direction. However, this restriction does not prevent you from specifying many rules in an ACL. You just have to put all of these rules into one ACL and apply it to an interface.

When a packet comes into the SSR at an interface where an inbound ACL is applied, the SSR compares the packet to the rules specified by that ACL. If it is permitted, the packet is allowed into the SSR. If not, the packet is dropped. If that packet is to be forwarded to go out of another interface (that is, the packet is to be routed) then a second ACL check is possible. At the output interface, if an outbound ACL is applied, the packet will be compared to the rules specified in this outbound ACL. Consequently, it is possible for a packet to go through two separate checks, once at the inbound interface and once more at the outbound interface.

When you apply an ACL to an interface, you can also specify whether the ACL can be modified or removed from the interface by an external agent (such as the Policy Manager

266 SmartSwitch Router User Reference Manual