Cisco WS-C2960-24TC-S Software Guide - Page 574

Understanding IPv6 Chapter 29 Configuring IPv6 Host Functions 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. ICMPv6 The Internet Control Message Protocol (ICMP) in IPv6 (RFC 2463) 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 (RFC 2461), 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), verify the reachability of the neighbor, and 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. The switch supports ICMPv6 redirect (RFC 2463) for routes with mask lengths less than 64. ICMP redirect is not supported for host routes or for summarized routes with mask lengths greater than 64. 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. 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 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 results 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 configures its own link-local address, and booting nodes send router solicitations to request router advertisements 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. 29-4 Catalyst 2960 Switch Software Configuration Guide OL-8603-04