> # Guidelines and Limitations

> Tip If IPv4-ACLs are already configured in a Gigabit Ethernet interface, you cannot add this interface to an Ethernet PortChannel group.

> Follow these guidelines when configuring IPv4-ACLs for Gigabit Ethernet interfaces:

> - Only use Transmission Control Protocol (TCP) or Internet Control Message Protocol (ICMP).

> Note Other protocols such as User Datagram Protocol (UDP) and HTTP are not supported in Gigabit Ethernet interfaces. Applying an ACL that contains rules for these protocols to a Gigabit Ethernet interface is allowed but those rules have no effect.

> - Apply IPv4-ACLs to the interface before you enable an interface. This ensures that the filters are in place before traffic starts flowing.
> - Be aware of the following conditions:
> - If you use the log-deny option, a maximum of 50 messages are logged per second.
> - The established, precedence, and fragments options are ignored when you apply IPv4-ACLs (containing these options) to Gigabit Ethernet interfaces.
> - If an IPv4-ACL rule applies to a preexisting TCP connection, that rule is ignored. For example if there is an existing TCP connection between A and B, and an IPv4-ACL specifies dropping all packets whose source is A and destination is B is subsequently applied, it will have no effect.

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