User's Manual

3/11/05 Client Location
OL-7426-02
Discover with a 0.0.0.0 client IP Address or a 169.254.*.* client auto-IP Address, or when the oper-
ator-set session timeout is exceeded.
Note that the Cisco 1030 remote edge lightweight access points at a remote location must be on the
same subnet to support roaming.
Inter-Subnet (Layer 3) RoamingInter-Subnet (Layer 3) Roaming
Similarly, in Multiple-Cisco Wireless LAN Controller Deployments, the Cisco SWAN supports client
roaming across Cisco 1000 Series lightweight access points managed by Cisco Wireless LAN Controllers
in the same Controller Mobility Group on different subnets. This roaming is transparent to the client,
because the session is sustained and a tunnel between the Cisco Wireless LAN Controllers allows the
client to continue using the same DHCP-assigned or client-assigned IP Address as long as the session
remains active. Note that the tunnel is torn down and the client must reauthenticate when the client
sends a DHCP Discover with a 0.0.0.0 client IP Address or a 169.254.*.* client auto-IP Address, or
when the operator-set session timeout is exceeded.
Note that the Cisco 1030 remote edge lightweight access points at a remote location must be on the
same subnet to support roaming.
Special Case: Voice Over IP Telephone RoamingSpecial Case: Voice Over IP Telephone Roaming
802.11 VoIP telephones actively seek out associations with the strongest RF signal to ensure best
Quality of Service (QoS) and maximum throughput. The minimum VoIP telephone requirement of
20 millisecond or shorter latency time for the roaming handover is easily met by the Cisco SWAN, which
has an average handover latency of nine or fewer milliseconds.
This short latency period is controlled by Cisco Wireless LAN Controllers, rather than allowing indepen-
dent APs to negotiate roaming handovers.
The Cisco SWAN supports 802.11 VoIP telephone roaming across Cisco 1000 Series lightweight access
points managed by Cisco Wireless LAN Controllers on different subnets, as long as the Cisco Wireless
LAN Controllers are in the same Controller Mobility Group. This roaming is transparent to the VoIP tele-
phone, because the session is sustained and a tunnel between Cisco Wireless LAN Controllers allows the
VoIP telephone to continue using the same DHCP-assigned IP Address as long as the session remains
active. Note that the tunnel is torn down and the VoIP client must reauthenticate when the VoIP
telephone sends a DHCP Discover with a 0.0.0.0 VoIP telephone IP Address or a 169.254.*.* VoIP
telephone auto-IP Address, or when the operator-set session timeout is exceeded.
About Client LocationClient Location
The Cisco SWAN periodically determines client location and stores the locations in the Cisco WCS
database. To view the client location history, display the Cisco WCS Monitor Client <client> -
<vendor:MACaddr> page and select Recent Map (High Resolution) or Present Map (High Resolution).
About External DHCP ServersExternal DHCP Servers
The Operating System is designed to appear as a DHCP Relay to the network and as a DHCP Server to
clients with industry-standard external DHCP Servers that support DHCP Relay. This means that each
Cisco Wireless LAN Controller appears as a DHCP Relay agent to the DHCP Server. This also means that
the Cisco Wireless LAN Controller appears as a DHCP Server at the virtual IP Address to wireless clients.
Because the Cisco Wireless LAN Controller captures the client IP Address obtained from a DHCP Server,
it maintains the same IP Address for that client during same-Cisco Wireless LAN Controller, inter-Cisco
Wireless LAN Controller, and inter-subnet Client Roaming
.