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 2 Cisco Unified Wireless Technology and Architecture
Roaming
Figure 2-8
Layer 2 Roam
When there are multiple WLCs connecting a WLAN to the same subnet and a client roams between APs
connected to different WLCs, a mobility announcement is exchanged between the WLCs. The mobility
announcement passes client-context information between WLCs.
connected to different WLCs, a mobility announcement is exchanged between the WLCs. The mobility
announcement passes client-context information between WLCs.
WLC to WLC Roaming Across Client Subnets
In cases where a client roams between APs that are connected to different WLCs and the client
subnet/VLAN is not the same between the WLCs, then a Layer 3 roam is performed. A mobility
announcement is exchanged between the 'roamed to' (foreign) WLC's mobility database and the home
(anchor) WLC's mobility database.
subnet/VLAN is not the same between the WLCs, then a Layer 3 roam is performed. A mobility
announcement is exchanged between the 'roamed to' (foreign) WLC's mobility database and the home
(anchor) WLC's mobility database.
A Layer 3 roam is more complex because the wireless client is moving from one VLAN/subnet to
another. Unless the WLAN system takes action to make the client subnet change transparent, the Layer
3 roam event has an adverse impact on client communication with upstream services. Existing client
sessions will either hang or eventually timeout and disconnect. The Cisco Unified Wireless solution uses
mobility tunnels to facilitate Layer 3 roaming that is transparent to the upstream network There are two
types of mobility tunnels:
another. Unless the WLAN system takes action to make the client subnet change transparent, the Layer
3 roam event has an adverse impact on client communication with upstream services. Existing client
sessions will either hang or eventually timeout and disconnect. The Cisco Unified Wireless solution uses
mobility tunnels to facilitate Layer 3 roaming that is transparent to the upstream network There are two
types of mobility tunnels:
•
Asymmetrical (default behavior – WLC Releases 4.0 and earlier)
•
Symmetrical (new option beginning with WLC Releases 4.1 and later)
Note
In WLC Release 4.1, asymmetrical tunneling is still the default behavior. Administrators must explicitly
configure symmetrical tunnel behavior.
configure symmetrical tunnel behavior.
Controller 1
Controller 2
190687
LWAPP
LWAPP
LWAPP
LWAPP
Client Database
MAC, WLAN, IP, Sec, ANCHOR...
Mobility
Announcement
Subnet A
Subnet B
AP A
AP B
AP C
AP D