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Configuring IPv6 Unicast Routing
Information About 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 drops any additional IPv6 packets
whose next hop is the same neighbor that the switch is actively trying to resolve. This drop avoids further load on the
CPU.
Default Router Preference
The switch supports IPv6 default router preference (DRP), an extension in router advertisement messages. DRP improves
the ability of a host to select an appropriate router, especially when the host is multihomed and the routers are on different
links. The switch does not support the Route Information Option in RFC 4191.
An IPv6 host maintains a default router list from which it selects a router for traffic to offlink destinations. The selected
router for a destination is then cached in the destination cache. NDP for IPv6 specifies that routers that are reachable or
probably reachable are preferred over routers whose reachability is unknown or suspect. For reachable or probably
reachable routers, NDP can either select the same router every time or cycle through the router list. By using DRP, you
can configure an IPv6 host to prefer one router over another, provided both are reachable or probably reachable.
IPv6 Stateless Autoconfiguration and Duplicate Address Detection
The switch uses stateless autoconfiguration to manage link, subnet, and site addressing changes, such as management
of host and mobile IP addresses. A host autonomously configures its own link-local address, and booting nodes send
router solicitations to request router advertisements for configuring interfaces.
IPv6 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
Dual IPv4 and IPv6 Protocol Stacks
You must use the dual IPv4 and IPv6 template to allocate hardware memory usage to both IPv4 and IPv6 protocols.
Figure 105 shows a router forwarding both IPv4 and IPv6 traffic through the same interface, based on the IP packet and
destination addresses.
Figure 105 Dual IPv4 and IPv6 Support on an Interface
Use the dual IPv4 and IPv6 switch database management (SDM) template to enable IPv6 routing dual stack environments
(supporting both IPv4 and IPv6).
122379
3ffe:yyyy::1
10.1.1.1
IPv6
IPv4
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