1-4
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 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.
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.
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.
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.
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.
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.
First Hop Security In IPv6
This section provides information about configuring the functions that comprise the first hop security
(FHS) feature in IPv6.
The functions available under FHS are also called as IPv6 policies. Policies can be applied at the
interface or VLAN level. IPv6 policies provide policy database services to features with regard to storing
and accessing those policies. Every time a policy is configured, the attributes of the policy are stored in
the software policy database. The policy is then applied to an interface and the software policy database
entry is updated to include this interface to which the policy is applied. You can use the following IPv6
policies:
• IPv6 Snooping, page 1-5
• IPv6 First-Hop Security Binding Table, page 1-5
• NDP Address Gleaning, page 1-5
• IPv6 DHCP Address Gleaning, page 1-6
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