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Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 36 Configuring IPv6 Unicast Routing
Understanding IPv6
Neighbor discovery throttling ensures that the switch CPU is not unnecessarily burdened while it is in
the process of obtaining the next hop forwarding information to route an IPv6 packet. The switch
performs a drop in hardware of any additional IPv6 packets whose next hop is the same neighbor the
CPU is actively resolving. Performing this drop avoids adding further load on the CPU and results in a
more efficient use of the switch CPU in an IPv6 routed environment.
IPv6 Stateless Autoconfiguration and Duplicate Address Detection
IPv6 supports two types of autoconfiguration:
•
Stateless autoconfiguration (RFC 2462), where a host autonomously configures its own link-local
address, and booting nodes send router solicitations to request router advertisements for configuring
interfaces
•
Stateful autoconfiguration using Dynamic Host Configuration Protocol (DHCP) v6.
The switch supports stateless autoconfiguration to manage link, subnet, and site addressing changes,
such as management of host and mobile IP addresses.
All interfaces on IPv6 nodes must have a link-local address, which is automatically configured from the
identifier (router MAC address) for an interface and the link-local prefix FE80::/10. A link-local address
enables a node to communicate with other nodes on the link and can be used to further configure the
node. Nodes can connect to a network and automatically generate global IPv6 addresses without the need
for manual configuration or the help of a server, such as a DHCP server. With IPv6, a router on the link
uses router advertisement messages to advertise global prefixes and its ability to act as a default router
for the link. A node on the link can automatically configure global IPv6 addresses by appending its
interface identifier (64-bits) to the prefixes (64 bits) included in the router advertisement messages.
The 128-bit IPv6 addresses configured by a node are then subjected to duplicate-address detection (RFC
2462) to ensure their uniqueness on the link. If the advertised prefixes are globally unique, the IPv6
addresses configured by the node are guaranteed to be globally unique. Router solicitation messages,
which have a value of 133 in the ICMP packet header Type field, are sent by hosts at system startup so
that the host can be immediately autoconfigured without waiting for the next scheduled router
advertisement message. IPv6 duplicate-address detection is performed on unicast addresses before they
are assigned to an interface. The switch does not support automatically generated site-local IPv6
addresses.
IPv6 Applications
The switch has IPv6 support for these applications:
•
Ping, traceroute, Telnet, TFTP, and FTP
•
Secure Shell (SSH) over an IPv6 transport
•
HTTP server access over IPv6 transport
•
DNS resolver for AAAA over IPv4 transport
•
Cisco Discovery Protocol (CDP) support for IPv6 addresses
For more information about managing these applications with Cisco IOS, see the “Managing Cisco IOS
Applications over IPv6” section in the
Cisco IOS IPv6 Configuration Library
at this URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/ipv6_c/sa_mgev6.htm
