Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter Guia Do Desenho
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Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 12 Cisco Unified Wireless and Mobile IP
Requirements for a Mobility Solution
Note
The location database discussed in this section has no relation to the location database as known in
location-based services (LBS) covered in
location-based services (LBS) covered in
Location Database
In the Cisco Unified Wireless Network, the first hop router receives packets for the wireless clients
through the routing protocol running on that network, and forwards them via a trunk to the WLC. Each
WLC keeps a database of wireless clients as they roam between APs registered to the WLC. If the
wireless client then roams to an AP on another WLC (a foreign WLC), that WLC can query other WLCs
in the mobility group to see if this is a new client or a roaming client. If it is a roaming client, the first
hop router near the home WLC still receives packets destined to the wireless client, but instead of the
WLC forwarding them on to one of its associated APs, it forwards the packets to the foreign WLC, which
then forwards them on to the client. Roaming on a Cisco Unified Wireless Network is covered in greater
depth in the
through the routing protocol running on that network, and forwards them via a trunk to the WLC. Each
WLC keeps a database of wireless clients as they roam between APs registered to the WLC. If the
wireless client then roams to an AP on another WLC (a foreign WLC), that WLC can query other WLCs
in the mobility group to see if this is a new client or a roaming client. If it is a roaming client, the first
hop router near the home WLC still receives packets destined to the wireless client, but instead of the
WLC forwarding them on to one of its associated APs, it forwards the packets to the foreign WLC, which
then forwards them on to the client. Roaming on a Cisco Unified Wireless Network is covered in greater
depth in the
For more information
.
In Mobile IP, the Home Agent (HA) contains the location database. Because it runs the network routing
protocol, it attracts packets for the Mobile IP Client and forwards them to the current location of the
client. Unlike the Cisco Unified Wireless Network, the HA does not maintain a distributed database
between WLCs. It does not query other HAs. As far as it is concerned, there is only one location
database: itself. This is where the location database mechanisms for the two solutions differ.
protocol, it attracts packets for the Mobile IP Client and forwards them to the current location of the
client. Unlike the Cisco Unified Wireless Network, the HA does not maintain a distributed database
between WLCs. It does not query other HAs. As far as it is concerned, there is only one location
database: itself. This is where the location database mechanisms for the two solutions differ.
Move Discovery, Location Discovery, and Update Signaling
When the wireless client roams to a new AP, it needs to associate to the wireless network. During the
association process, the association packets are forwarded to the WLC to identify the wireless client and
the location (AP) from where the wireless client is trying to associate. This information is used by the
WLC to update its location database (the WLC mobility database). If the client has roamed to another
WLC, the original WLC for the wireless client forwards packets destined to the wireless client to the
remote WLC.
association process, the association packets are forwarded to the WLC to identify the wireless client and
the location (AP) from where the wireless client is trying to associate. This information is used by the
WLC to update its location database (the WLC mobility database). If the client has roamed to another
WLC, the original WLC for the wireless client forwards packets destined to the wireless client to the
remote WLC.
In Mobile IP, the Mobile IP Client joining the wireless network does not provide the HA with any
information. Additionally, the client is responsible for recognizing when it has moved between networks.
The client typically detects movement in two ways. One way is through the Windows operating system’s
Layer 2 notification feature called Media Sense. This feature detects disconnect and reconnect of
different Layer 2 media when roaming between APs and sends the Windows operating system a signal
when it occurs. This allows the interface to try and renegotiate its DHCP address with the DHCP server.
The second method for detecting movement is through Foreign Agent (FA) advertisements. These
advertisements tell the Mobile IP Client which subnet it is on. If the Mobile IP Client receives one of
these periodic messages, it can tell it has moved to a new subnet. These move discovery methods are
typically used for Mobile IP. There are other methods specified in RFC 3344, but generally these are not
used.
information. Additionally, the client is responsible for recognizing when it has moved between networks.
The client typically detects movement in two ways. One way is through the Windows operating system’s
Layer 2 notification feature called Media Sense. This feature detects disconnect and reconnect of
different Layer 2 media when roaming between APs and sends the Windows operating system a signal
when it occurs. This allows the interface to try and renegotiate its DHCP address with the DHCP server.
The second method for detecting movement is through Foreign Agent (FA) advertisements. These
advertisements tell the Mobile IP Client which subnet it is on. If the Mobile IP Client receives one of
these periodic messages, it can tell it has moved to a new subnet. These move discovery methods are
typically used for Mobile IP. There are other methods specified in RFC 3344, but generally these are not
used.
Location discovery is typically done in one of two ways in Mobile IP. In the first method, the Mobile IP
Client receives an FA advertisement telling it what the IP address is for the FA. The Mobile IP Client
can check this address against the address it already has from the FA and tell if the FA advertisement is
from a new FA. The Mobile IP Client can then forward this IP address to its HA so that the HA can build
a new tunnel to the new FA and proceed forward packets to the Mobile IP Client. In the second method,
Client receives an FA advertisement telling it what the IP address is for the FA. The Mobile IP Client
can check this address against the address it already has from the FA and tell if the FA advertisement is
from a new FA. The Mobile IP Client can then forward this IP address to its HA so that the HA can build
a new tunnel to the new FA and proceed forward packets to the Mobile IP Client. In the second method,