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Cisco Catalyst Switch Module 3110 and 3012 for IBM BladeCenter Software Configuration Guide
OL-12189-01
Chapter 39 Configuring IPv6 Host Functions and Unicast Routing
Understanding IPv6
See the section on IPv6 Unicast Addresses in the “Implementing Addressing and Basic Connectivity for
IPv6” chapter in the Cisco IOS IPv6 Configuration Library at this URL:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00807fcf4b.
html
Each IPv6 host interface can support up to three addresses in hardware (one aggregatable global unicast
address, one link-local unicast address, and zero or more privacy addresses).
DNS for IPv6
IPv6 introduces new Domain Name System (DNS) record types that are supported in the DNS
name-to-address and address-to-name lookup processes. The new 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 Catalyst Switch Module 3110 supports advertising the system 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.
ICMPv6
The Internet Control Message Protocol (ICMP) in IPv6 functions the same as in IPv4. ICMP 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. A value of 58 in the Next Header field of the basic IPv6 packet header identifies
an IPv6 ICMP packet.
Neighbor Discovery
The switch supports Neighbor Discovery Protocol (NDP) for IPv6, a protocol running on top of ICMPv6,
and Static Neighbor Discovery 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.
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 solicitation 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.
Routers send neighbor-redirect messages to inform hosts 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.
