Configuring Layer 3 Mobility - Brocade Communications Systems RFS6000 System Reference Manual

5

Configuring Layer 3 Mobility

Layer 3 mobility is a mechanism enabling a client to maintain the same Layer 3 address while
roaming throughout a multi-VLAN network. This enables transparent routing of IP datagrams to
Clients during their movement, so data sessions can be maintained while they roam (in for voice
applications in particular). Layer 3 mobility maintains TCP/UDP sessions in spite of roaming among
different IP subnets.
A mobility domain comprises of a network of switches among which a client can roam seamlessly
without changing its IP address. Each switch in the mobility domain needs a mobility domain string
identifier so Clients roaming between switches can retain their Layer 3 address and maintain
application-layer connectivity.
When a client enters a mobility domain (by associating with a switch), it is first assigned a home
switch. The home switch is responsible for assigning a VLAN for the client and communicating the
client's mobility-related parameters to the other switches in the mobility domain. The home switch
does not change for the remainder of the client's presence in the mobility domain. All data packets
transmitted/received by the client including DHCP and ARP are tunneled through the home switch.
The IP address for the client is assigned from the VLAN to which the client belongs (as determined
by the home switch).
The current switch is the switch in the mobility domain a client is currently associated to. The
current switch changes as the client roams and establishes different associations. The current
switch is responsible for delivering data packets from the client to its home switch and vice-versa.
CAUTION
An Access Port is required to have a DHCP provided IP address before attempting layer 3
adoption, otherwise it will not work. Additionally, the Access Port must be able to find the IP
addresses of the switches on the network.
To locate switch IP addresses on the network:
- Configure DHCP option 189 to specify each switch IP address.
- Configure a DNS Server to resolve an existing name into the IP of the switch. The Access Port
has to get DNS server information as part of its DHCP information. The default DNS name
requested by an Brocade Mobility 300 Access Point is "Symbol-CAPWAP-Address". However, since
the default name is configurable, it can be set as a factory default to whatever value is needed.
Key aspects of Layer 3 Mobility include:
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Seamless client roaming between switches on different Layer 3 subnets, while retaining the
same IP address.
Static configuration of mobility peer switches.
Layer 3 support does not require any changes to the client. In comparison, other solutions
require special functionality and software on the client. This creates numerous inter-working
problems with working with Clients from different legacy devices which do not support Layer 2
switching.
Support for a maximum of 15 peers. The maximum roamed clients for L3 mobility is limited to
the number of clients for that RFS controller.
A full mesh of GRE tunnels can be established between mobility peers. Each tunnel is between
a pair of switches and can handle data traffic for all Clients (for all VLANs) associated directly
or indirectly with the client.
Brocade Mobility RFS4000, RFS6000, and RFS7000 System Reference Guide
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