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39-15
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
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:
To return to the default configuration, use the no ipv6 icmp error-interval global 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-routing global configuration command, and you must configure an IPv6 address
and IPv6 processing on an interface by using the ipv6 address interface configuration command.
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.