ICMPv6
Like ICMP for IPv4, ICMPv6 provides messaging support for IPv6. As you learned in the previous
section, ICMPv6 provides all the underlying services for neighbor discovery, but it also provides
many functions in error reporting and echo requests.
ICMPv6 is standardized in RFC 2463, which broadly classifies ICMPv6 messages into two
groups: error reporting messages and informational messages. To conserve bandwidth, RFC 2463
mandates configurable rate limiting of ICMPv6 error messages. The RFC suggests that ICMPv6
may limit its message rate by means of timers or based on bandwidth. No matter which methods
are used, each implementation must support configurable settings for these limits. To that end,
Cisco IOS Software implements ICMP rate limiting by setting the minimum interval between
error messages and allows credit to build using a token bucket.
To limit ICMPv6 error messages, use the ipv6 icmp error-interval command, in global
configuration mode. The default interval is 100 ms, and the default token-bucket size is 10 tokens.
With this configuration, a new token (up to a total of 10) is added to the bucket every 100 ms.
Beginning when the token bucket is full, a maximum of 10 ICMPv6 error messages can be sent in
rapid succession. Once the token bucket empties, the router cannot send any additional ICMPv6
error messages until at least one token is added to the bucket.