Cisco Systems 3560 Manual De Usuario
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Catalyst 3560 Switch Software Configuration Guide
OL-8553-06
Chapter 37 Configuring IPv6 Unicast Routing
Understanding IPv6
DNS for IPv6
IPv6 supports Domain Name System (DNS) record types in the DNS name-to-address and
address-to-name lookup processes. The DNS AAAA resource record types support IPv6 addresses and
are equivalent to an A address record in IPv4. The switch supports DNS resolution for IPv4 and IPv6.
address-to-name lookup processes. The DNS AAAA resource record types support IPv6 addresses and
are equivalent to an A address record in IPv4. The switch supports DNS resolution for IPv4 and IPv6.
Path MTU Discovery for IPv6 Unicast
The switch supports advertising the system maximum transmission unit (MTU) to IPv6 nodes and path
MTU discovery. Path MTU discovery allows a host to dynamically discover and adjust to differences in
the MTU size of every link along a given data path. In IPv6, if a link along the path is not large enough
to accommodate the packet size, the source of the packet handles the fragmentation. The switch does not
support path MTU discovery for multicast packets.
MTU discovery. Path MTU discovery allows a host to dynamically discover and adjust to differences in
the MTU size of every link along a given data path. In IPv6, if a link along the path is not large enough
to accommodate the packet size, the source of the packet handles the fragmentation. The switch does not
support path MTU discovery for multicast packets.
ICMPv6
The Internet Control Message Protocol (ICMP) in IPv6 generates error messages, such as ICMP
destination unreachable messages, to report errors during processing and other diagnostic functions. In
IPv6, ICMP packets are also used in the neighbor discovery protocol and path MTU discovery.
destination unreachable messages, to report errors during processing and other diagnostic functions. In
IPv6, ICMP packets are also used in the neighbor discovery protocol and path MTU discovery.
Neighbor Discovery
The switch supports NDP for IPv6, a protocol running on top of ICMPv6, and static neighbor entries for
IPv6 stations that do not support NDP. The IPv6 neighbor discovery process uses ICMP messages and
solicited-node multicast addresses to determine the link-layer address of a neighbor on the same network
(local link), to verify the reachability of the neighbor, and to keep track of neighboring routers.
IPv6 stations that do not support NDP. The IPv6 neighbor discovery process uses ICMP messages and
solicited-node multicast addresses to determine the link-layer address of a neighbor on the same network
(local link), to verify the reachability of the neighbor, and to keep track of neighboring routers.
The switch supports ICMPv6 redirect for routes with mask lengths less than 64 bits. ICMP redirect is
not supported for host routes or for summarized routes with mask lengths greater than 64 bits.
not supported for host routes or for summarized routes with mask lengths greater than 64 bits.
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.
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.
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.
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.
For more information about DRP for IPv6, see the “Implementing IPv6 Addresses and Basic
Connectivity” chapter in the Cisco IOS IPv6 Configuration Library on Cisco.com.
Connectivity” chapter in the Cisco IOS IPv6 Configuration Library on Cisco.com.