Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
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Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 12 Cisco Unified Wireless and Mobile IP
Roaming on a Mobile IP-enabled Network
Figure 12-4
Roaming on a Cisco Unified Wireless Network
If the client requests a DHCP address, the WLC either gives the client an address from its local DHCP
pool (if defined) or fills in the gateway address in the DHCP request for an external DHCP server. In
either case, the WLC modifies any returning DHCP offers so that the DHCP server’s address is set to the
address on WLCs virtual interface. Even though the virtual IP address is not in any routing table
(typically 1.1.1.1), it still allows the WLC to intercept any DHCP renewals on wireless clients that occur
with the Microsoft Windows operating system (using Microsoft Media Sense) when it roams between
APs. In addition, if the same address is on all WLCs’ virtual interfaces, it allows other WLCs to intercept
the DHCP renewal from the client when it roams to a new AP associated to a different WLC.
pool (if defined) or fills in the gateway address in the DHCP request for an external DHCP server. In
either case, the WLC modifies any returning DHCP offers so that the DHCP server’s address is set to the
address on WLCs virtual interface. Even though the virtual IP address is not in any routing table
(typically 1.1.1.1), it still allows the WLC to intercept any DHCP renewals on wireless clients that occur
with the Microsoft Windows operating system (using Microsoft Media Sense) when it roams between
APs. In addition, if the same address is on all WLCs’ virtual interfaces, it allows other WLCs to intercept
the DHCP renewal from the client when it roams to a new AP associated to a different WLC.
The wireless client can easily roam between any APs registered to the WLC because the WLC simply
keeps track of the wireless client’s current location and forwards the packets destined to that client into
the correct LWAPP tunnel and on to the associated AP. When the client roams to an AP registered to a
different WLC, the remote WLC queries the mobility group to see if the client has roamed. If so, an
Ethernet-over-IP tunnel is set up to forward client traffic from the original WLC to the WLC registered
to the AP with which the client is currently associated.
keeps track of the wireless client’s current location and forwards the packets destined to that client into
the correct LWAPP tunnel and on to the associated AP. When the client roams to an AP registered to a
different WLC, the remote WLC queries the mobility group to see if the client has roamed. If so, an
Ethernet-over-IP tunnel is set up to forward client traffic from the original WLC to the WLC registered
to the AP with which the client is currently associated.
Traffic originating from the wireless client that has roamed to an AP associated to another WLC can be
handled in two ways. Typically, the foreign WLC modifies the destination MAC address of any packet
from the wireless client to be its gateway MAC address before forwarding it on. The second method
occurs if mobility anchoring is enabled on the original WLC. In this case, the traffic is forwarded back
to the original WLC. This allows traffic to be sent to the correct gateway in case address policies such
as Reverse Path Forwarding (RPF) checks are enabled.
handled in two ways. Typically, the foreign WLC modifies the destination MAC address of any packet
from the wireless client to be its gateway MAC address before forwarding it on. The second method
occurs if mobility anchoring is enabled on the original WLC. In this case, the traffic is forwarded back
to the original WLC. This allows traffic to be sent to the correct gateway in case address policies such
as Reverse Path Forwarding (RPF) checks are enabled.
For more information about Cisco Unified Wireless Roaming, see
.
Roaming on a Mobile IP-enabled Network
A Mobile IP-enabled network has three components:
•
Mobile node (MN)—Mobile IP Clients
•
Home Agent (HA)—Contains the location database for MNs advertises reachability to the MN in
the Interior Gateway Protocol (IGP). It also tunnels packets to MN.
the Interior Gateway Protocol (IGP). It also tunnels packets to MN.
•
Foreign Agent (FA)—(Optional) offloads CPU processing of encapsulation and decapsulation from
the MN and saves IP address space. FAs are not often deployed in enterprise campus environments.
the MN and saves IP address space. FAs are not often deployed in enterprise campus environments.
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Controller tunnels
packet to AP where
wireless client
is associated
Router attracts
Packets for wireless
Clients via the IGP
AP de-encapsulates
packets and forwards
them to wireless clients