IPv6 client mobility

A client mobility is a wireless network feature that

• supports seamless Layer 2 and Layer 3 roaming for IPv6-only and dual-stack clients

• manages IPv6 client addresses and Neighbor Discovery (NDP) packet handling across controllers, and

• retains the client's IP address and application connectivity as they move between access points and switches in the mobility group.

Link layer mobility is not sufficient for wireless client Layer 3 applications to work seamlessly while roaming. Cisco IOSd’s wireless mobility module uses mobility tunneling to retain seamless connectivity for the client’s Layer 3 PoP (point of presence) when the client roams across different subnets on different switches.

IPv6 is the next-generation network layer Internet protocol intended to replace IPv4 in the TCP/IP suite of protocols. This new version increases the global internet address space to accommodate users and applications that require unique global IP addresses. IPv6 incorporates 128-bit source and destination addresses, which provide significantly more addresses than the 32-bit IPv4 addresses.

To support IPv6 clients across controllers, ICMPv6 messages must be handled in a specific way to ensure the IPv6 client remains on the same Layer 3 network. The device keeps track of IPv6 clients by intercepting ICMPv6 messages to provide seamless mobility and protect the network from network attacks. Neighbor Discovery Protocol (NDP) packets are converted from multicast to unicast and delivered individually to each client. This unique solution ensures that Neighbor Discovery and Router Advertisement packets are not leaked across VLANs. Clients receive specific Neighbor Discovery and Router Advertisement packets, ensuring correct IPv6 addressing and avoiding unnecessary multicast traffic.

The configuration for IPv6 mobility is the same as for IPv4 mobility and does not require separate software on the client side to achieve seamless roaming. The device must be part of the same mobility group. Both IPv4 and IPv6 client mobility are enabled by default.

IPv6 client mobility provides these features:

• Retains multiple client IPv6 addresses during Layer-2 and Layer-3 roaming.

• Manages IPv6 Neighbor Discovery Protocol (NDP) packets.

• Learns client IPv6 addresses.

The Neighbor Discovery Protocol (NDP) is a protocol that

• operates at the link layer and manages the discovery of other nodes on the network link

• determination of their link-layer addresses, identification of available routers, and

• the maintenance of reachability information for neighboring nodes.

A Router Advertisement (RA) is an IPv6 Neighbor Discovery Protocol (NDP) message

• sent by routers to communicate network parameters such as available routers

• network prefixes for IPv6 address configuration, and

• link MTU information to hosts on the link.

RAs play a vital role in this process by allowing hosts to detect routers, generate IPv6 addresses, and configure other connection parameters.

Routers send RAs either on a regular basis or in response to Router Solicitation messages from hosts.

IPv6 wireless client mobility manages the IPv6 RA packet. The device forwards the link-local all-nodes multicast RA packets to both local and roaming wireless nodes mapped on the same VLAN where the RA was received.

Figure 1 illustrates how a roaming client “MN” receives RA from VLAN 200 in a foreign controller and how it acquires an new IP address and breaks into L3 mobility's point of presence.

IPv6 address learning is the process

• by which IPv6 clients acquire IP addresses, and

• network devices such as switches or controllers, observe and record these assignments.

There are three ways for an IPv6 client to acquire IPv6 addresses:

• Stateless Address Auto-Configuration (SLAAC)

• Stateful DHCPv6

• Static configuration

For these methods, the IPv6 client always sends NS DAD (duplicate address detection) to ensure that there is no duplicated IP address on the network. The device snoops the client's NDP and DHCPv6 packets to learn about the client's IP addresses. It then updates the controller's database. The database then informs the controller about the client's new IP address.

An IP address is a network identifier that

• uniquely distinguishes a device on a network

• supports both IPv4 and IPv6 formats, and

• can be dynamically assigned, updated, or displayed for client devices.

If a new IP address is received after the RUN state, whether it is an addition or removal, the controller updates its local database with the new IP addresses for display purposes. IPv6 uses the same PEM state machine code flow as IPv4. When external entities, such as Prime Infrastructure, request IP addresses, the controller includes all available IPv4 and IPv6 addresses in the API or SPI interface response.

An IPv6 client can acquire multiple IP addresses from the stack for different purposes. For example, a client may have a link-local address for local traffic and a routable unique local or global address.

When the client is in the DHCP request state and the controller receives the first IP address notification from the database, for either an IPv4 or IPv6 address, the PEM moves the client into the RUN state.

If a new IP address is received after the RUN state, whether it is an addition or removal, the controller updates its local database with the new IP addresses for display purposes.

When external entities, such as Prime Infrastructure, request IP addresses, the controller provides all available IPv4 and IPv6 addresses.

A IPv6 configuration is a network setup that

• enables seamless support for IPv6 clients alongside IPv4 clients

• requires manual VLAN configuration by the administrator to activate IPv6 features, and

• implements snooping and throttling functionality to manage NDP packets between the switch controller device and its clients.