Cisco Systems 3750E Configuring IPv6 Icmp Rate Limiting, Configuring CEF and dCEF for IPv6, 39-15

Chapter 39 Configuring IPv6 Unicast Routing

Configuring IPv6

Configuring IPv6 ICMP Rate Limiting

IPv6 ICMP rate limiting uses a token-bucket algorithm for limiting the rate at which IPv6 ICMP error messages are sent to the network. The interval between error messages is specified in a time interval and a bucket size. Because some applications, such as traceroute, sometimes require replies to a group of requests to be sent out in rapid succession, specifying only the interval between error messages can cause the application to fail. The token bucket allows a number of tokens, each representing the ability to send one error message, to be stored in virtual buckets. For every message to be sent, one token is removed from the bucket. If a series of error messages is generated, error messages can be sent until the bucket is empty. When the bucket is empty, IPv6 ICMP error messages are not sent until a new token is placed in the bucket. This method does not increase the average rate-limiting time interval, but it provides more flexibility than fixed-time intervals.

ICMP rate limiting is enabled by default with a default interval between error messages of 100 milliseconds and a bucket size (maximum number of tokens to be stored in a bucket) of 10.

Beginning in privileged EXEC mode, follow these steps to change the ICMP rate-limiting parameters:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	ipv6 icmp error-interval interval [bucketsize]	Configure the interval and bucket size for IPv6 ICMP error
		messages:
		• interval—The interval (in milliseconds) between tokens
		being added to the bucket. The range is from 0 to
		2147483647 milliseconds.
		• bucketsize—(Optional) The maximum number of tokens
		stored in the bucket. The range is from 1 to 200.
Step 3
	end	Return to privileged EXEC mode.
Step 4
	show ipv6 interface [interface-id]	Verify your entries.
Step 5
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return to the default configuration, use the no ipv6 icmp error-intervalglobal configuration command.

This example shows how to configure an IPv6 ICMP error message interval of 50 milliseconds and a bucket size of 20 tokens.

Switch(config)#ipv6 icmp error-interval 50 20

Configuring CEF and dCEF for IPv6

Cisco Express Forwarding (CEF) is a Layer 3 IP switching technology used to optimize network performance. CEF implements an advanced IP look-up and forwarding algorithm to deliver maximum Layer 3 switching performance. It is less CPU-intensive than fast-switching route-caching, allowing more CPU processing power to be dedicated to packet forwarding. In a Catalyst 3750-E switch stack, the hardware uses distributed CEF (dCEF) in the stack. IPv4 CEF and dCEF are enabled by default. IPv6 CEF and dCEF are disabled by default, but automatically enabled when you configure IPv6 routing.

To route IPv6 unicast packets, you must first globally configure forwarding of IPv6 unicast packets by using the ipv6 unicast-routingglobal configuration command, and you must configure an IPv6 address and IPv6 processing on an interface by using the ipv6 address interface configuration command.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		39-15