Implementing IBM System Networking 10Gb Ethernet Switches

Chapter 2. IBM System Networking Switch 10Gb Ethernet switch features 73

Anycast addresses are allocated from the unicast address space, using any of the defined

unicast address formats. Thus, anycast addresses are syntactically indistinguishable from

unicast addresses. When a unicast address is assigned to more than one interface, thus

turning it into an anycast address, the nodes to which the address is assigned must be

configured to know that it is an anycast address.

2.5.3 IPv6 address auto-configuration

IPv6 supports the following types of address autoconfiguration:

򐂰 Stateful address configuration

Address configuration is based on the use of a stateful address configuration protocol,

such as DHCPv6, to obtain addresses and other configuration options.

򐂰 Stateless address configuration

Address configuration is based on the receipt of Router Advertisement messages that

contain one or more Prefix Information options.

IBM System Networking switches support stateless address configuration. Stateless address

configuration allows hosts on a link to configure themselves with link-local addresses and with

addresses derived from prefixes advertised by local routers. Even if no router is present,

hosts on the same link can configure themselves with link-local addresses and communicate

without manual configuration

2.5.4 Neighbor Discovery protocol

The switch uses Neighbor Discovery protocol (ND) to gather information about other router

and host nodes, including the IPv6 addresses. Host nodes use ND to configure their

interfaces and perform health detection. ND allows each node to determine the link-layer

addresses of neighboring nodes, and to track each neighbor’s information. A neighboring

node is a host or a router that is linked directly to the switch. The switch supports Neighbor

Discovery, as described in RFC 4861 (http://www.ietf.org/rfc/rfc4861.txt).

Neighbor Discover messages allow network nodes to exchange information, as follows:

򐂰 Neighbor Solicitations allow a node to discover information about other nodes.

򐂰 Neighbor Advertisements are sent in response to Neighbor Solicitations. The Neighbor

Advertisement contains information required by nodes to determine the link-layer address

of the sender, and the sender’s role on the network.

򐂰 IPv6 hosts use Router Solicitations to discover IPv6 routers. When a router receives a

Router Solicitation, it responds immediately to the host.

򐂰 A router uses Router Advertisements to announce its presence on the network, and to

provide its address prefix to neighbor devices. IPv6 hosts listen for Router

Advertisements, and uses the information to build a list of default routers. Each host uses

this information to perform auto-configuration of IPv6 addresses.

򐂰 Redirect messages are sent by IPv6 routers to inform hosts of a better first-hop address

for a specific destination. Redirect messages are only sent by routers for unicast traffic,

are only unicast to originating hosts, and are only processed by hosts.