Dell PowerConnect W-Series Instant Access Point 6.1.3.4-3.1.0.0 | User Guide Layer-3 Mobility | 93Chapter 6Layer-3 MobilityIAPs form a single Instant network when they are in the same L2 domain. As the number of clients increase,multiple subnets are required to avoid broadcast overhead. In such a scenario, a client should be allowed to roamaway from the Instant network to which it first connected (home network) to another Instant network supportingthe same WLAN access parameters (foreign network) and continue its existing sessions.Layer-3 mobility allows a client to roam without losing its IP address and sessions. If WLAN access parameters aresame across these networks, clients connected to APs in a given Instant network can roam to APs in a foreignInstant network and continue their existing sessions. Clients roaming across these networks are able to continueusing their IP addresses after roaming. You can configure a list of Virtual Controller IP addresses across which L3mobility is supported.OverviewDell Instant layer-3 mobility solution defines a Mobility Domain as a set of Instant networks, with same WLANaccess parameters, across which client roaming is supported. The Instant network to which the client firstconnects is called its home network. When the client roams to a foreign network, an AP in the home network(home AP) anchors all traffic to or from this client. The AP to which the client is connected in the foreignnetwork (foreign AP) tunnels all client traffic to or from the home AP through a GRE tunnel.Figure 83 Shows the routing of traffic when the client is away from its home networkWhen a client first connects to an Instant network, a message is sent to all configured Virtual Controller IPaddresses to see if this is an L3 roamed client. On receiving an acknowledgement from any of the configuredVirtual Controller IP addresses, the client is identified as an L3 roamed client. If the AP has no GRE tunnel tothis home network, a new tunnel is formed to an AP (home AP) from the client's home network.Each foreign AP has only one home AP per Instant network to avoid duplication of broadcast traffic. SeparateGRE tunnels are created for each foreign AP / home AP pair. If a peer AP is a foreign AP for one client and a homeAP for another, two separate GRE tunnels are used to handle L3 roaming traffic between these APs.
