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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter39 Configuring IPv6 Unicast Routing
Understanding IPv6
A value of 135 in the Type field of the ICMP packet header identifies a neighbor solicitation message.
These messages are sent on the local link when a node needs to determine the link-layer address of
another node on the same local link. When a destination node receives a neighbor solicitati on message,
it replies by sending a neighbor advertisement message, which has a value of 136 in the ICMP packet
header Type field.
A value of 137 in the ICMP packet header Type field identifies an IPv6 neighbor redirect message. The
switch supports ICMPv6 redirect (RFC 2463). Routers send neighbor-redirect messages to inform h osts
of better first-hop nodes on the path to a destination. A router does not update its routing tables after
receiving a neighbor-redirect message and hosts do not originate neighbor-redirect messages.
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 r oute 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 r esults 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 c onfigures its own link-local
address, and booting nodes send router solicitations to request router advertis ements 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 globa l 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 un ique. 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 route r
advertisement message. IPv6 duplicate-address detection is performed on unicast a ddresses 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