Table of contents
Basic concept of Wlan service set
Basic Concepts of Wireless Roaming
Classification of Wireless Roaming
Data Forwarding Path for Wireless Roaming
Layer 2 Local Forwarding Roaming
Layer 3 local forwarding roaming
Layer 2/3 centralized forwarding roaming
Basic concept of Wlan service set
| concept |
full name |
describe |
| BSS |
Basic Service Set BSS |
Basic Service Unit for Wireless Networks It can be understood that 1 AP is 1 BSS |
| ESS |
Extended Service Set ESS |
Composed of multiple BSSs using the same SSID ( a wireless network composed of multiple APs sending out wireless signals with the same name ; solving the problem of limited coverage of a single BSS) |
| SSID |
Service Set Identifier SSID |
The name of the wireless network, used to distinguish different wireless networks 1 AP can send multiple wireless signals, each signal has its own SSID, and the SSIDs of different signals can be the same or different |
| ESSID |
Extended Service Set Identifier ESSID |
The identifier of one or a group of wireless networks, which is the same as SSID. |
| BSSID |
Basic Service Set Identifier BSSID |
It is used on the link layer to distinguish different wireless signals on the same AP ( each signal sent by the AP has a unique BSSID; that is, different signals on the same AP can be distinguished by BSSID ) It can also be used to distinguish the BSS in the same ESS ( when different APs send out multiple identical SSIDs to form a large wireless network, you can use the BSSID to distinguish which AP sent the signal ) |
| Wlan ID |
virtual access point |
The business function entity virtualized on the AP device (configure the parameters of the wireless signal in the Wlan ID) For example: the SSID of the wireless signal can be configured through the Wlan ID, and the BSSID corresponding to the wireless signal will be automatically generated after configuration |
Basic Concepts of Wireless Roaming
What is wireless roaming
When the STA moves to the critical area of the coverage of two APs, the STA actively re-associates with the new AP and disconnects from the original AP. )
Problems Solved by Wireless Roaming
1. The authentication time during roaming is too long, resulting in packet loss or even service interruption
2. The IP address does not change before and after roaming (the TCP session is not re-established)
3. Ensure that the user's authorization information does not change
Handover process of wireless roaming (realized by management frame - reassociation request frame)
detection signal,
The STA detects the Beacon frame about the AP received by each channel, and according to the wireless signal strength carried by the frame, finds out whether there is an AP that meets the roaming threshold condition set by the terminal, and when a new AP meets the requirement, it sends a Probe request to the new AP; After the AP receives the response, the terminal evaluates the received response and selects one for re-association
wireless roaming roles
HAC、HAP、FAC、FAP
HAC (Home AC): Home AC, the AC to which the terminal belongs before roaming
HAP (Home AP): Home AP, the AP that the terminal belongs to before roaming
FAC (Foreign AC): Foreign AC, the AC to which the terminal belongs after roaming
FAP (Foreign AP): Foreign AP, the AP to which the terminal belongs after roaming
Conditions for implementing roaming
1. The roaming APs must use the same SSID, security template (authentication encryption method and parameters), etc.
2. The data forwarding mode between roaming APs should be consistent (both local or centralized)
3. There must be signal coverage overlapping areas between roaming APs
4. The software platforms of roaming APs should be consistent
Other Technical Terms for Wireless Roaming
CTI: CAPWAP tunnel interface identifier (only valid locally, unique locally)
VID: Vlan ID of the wireless user (business Vlan)
MTI: the identifier of the roaming tunnel interface between ACs (only valid locally, unique locally)
view configuration
Ruijie equipment
show lsm interface View the digital ID of the tunnel interface
Classification of Wireless Roaming
Classified according to whether the service VLAN of the terminal changes before and after roaming
The IP address will never change, but the Vlan to which this address belongs will change
Layer 2 roaming: The VLAN to which the terminal belongs will not change before and after roaming
Layer 3 roaming: The Vlan to which the terminal belongs will change before and after roaming
According to whether the AC of the terminal changes before and after roaming
Roaming within an AC : The AC to which the terminal belongs remains unchanged before and after roaming, HAC=FAC
Roaming between ACs : Changes in the AC to which the terminal belongs before and after roaming
Roaming between ACs requires the configuration of a roaming group
Establishing an AC roaming tunnel (CAPWAP tunnel) between ACs in a roaming group
The role of roaming groups
1. Distinguish whether a terminal is a roaming terminal; if a terminal connects to an AC from one terminal, the AC will notify the AC in the roaming group to ask if there is any information about the terminal. If so, it means that the terminal is a roaming terminal
2. Synchronize terminal information when roaming between ACs
3. Transmit data information of the terminal when roaming between ACs
Configuration of roaming groups
Configuration of Ruijie and Huawei equipment
mobility-group 123
member Peer address (the address of the peer AC to establish the CAPWAP tunnel—generally LOOP0 address)
Notes on roaming groups
1. ACs in the same roaming group must use the same software version
2. ACs in the same roaming group need to configure the same roaming group name when configuring the roaming group
Data Forwarding Path for Wireless Roaming
Roaming is initiated by the terminal, focusing on the difference in data sending and receiving channels after roaming (different roaming types have different forwarding channels)
Layer 2 Local Forwarding Roaming
Layer 2 roaming within an AC - local forwarding
Before roaming: STA→HAP→Internet
After roaming: STA→FAP→Internet
Layer 2 Roaming Between ACs —Local Forwarding
Before roaming: STA→HAP→Internet
After roaming: STA→FAP→Internet
Layer 3 local forwarding roaming
Layer 3 roaming within the AC - local forwarding (APs need to communicate with each other)
Before roaming: STA→HAP→Internet
STA sends data from HAP, Vlan Tag is x
After roaming: ST→FAP→HAP→Internet (the roaming tunnel between APs is established automatically, no additional configuration is required; the roaming entry on the AP will record the VID of the STA before and after roaming, and the address of the AP before and after roaming)
- STA sends data to FAP (AP2), FAP encapsulates the data into CAPWAP tunnel and sends it to HAP, the source is FAP, the destination is HAP (Vlan Tag is y--business Vlan)
- The data reaches the HAP (AP1) through the three layers, and the HAP decapsulates the STA data frame for normal forwarding (Vlan Tag is x--business Vlan)
- The packets returned from the external network are first sent to the HAP, and the HAP encapsulates the data frame into the tunnel between APs and sends it to the FAP (Vlan Tag is x--business Vlan)
- After FAP decapsulates, send the data frame to STA (Vlan tag is y--business Vlan)
Layer 3 Roaming Between ACs - Local Forwarding
Before roaming: STA→HAP→Internet
After roaming: ST→FAP→FAC→HAC→HAP→Internet
- The STA sends the data from the FAP and encapsulates it to the FAC through the CAPWAP tunnel (Vlan Tag is the business Vlan)
- FAC sends the data to HAC through CAPWAP (Vlan Tag is the Vlan to which the roaming group address belongs)
- HAC sends data to HAP through CAPWAP (Vlan Tag is the Vlan to which the roaming group address belongs)
- After HAP receives the data, it normally forwards the data (Vlan Tag is the business Vlan)
Layer 2/3 centralized forwarding roaming
Layer 2/3 roaming within an AC ——centralized forwarding
Data traffic after roaming
- STA sends the data after roaming to AP2, AP2 finds that this terminal is a roaming terminal, and encapsulates the data to AC through CAPWAP tunnel (Vlan is the Vlan where AP is located)
- After the AC receives the message, it will modify the message coming from the CT2 port to enter the AC from the CT1 port.
- Then the AC forwards the data normally (Vlan is the Vlan where the outgoing interface is located)
Layer 2/3 roaming between ACs - centralized forwarding
- STA forwards the data to AP2, and AP2 encapsulates it to AC2 through the CAPWAP tunnel (Vlan is the Vlan where AP2 is located)
- AC2 also sends to AC1 through the CAPWAP tunnel (Vlan is the Vlan where the roaming group address is located)
- After AC1 receives it, it directly forwards it normally (Vlan is the Vlan where the outgoing interface address is located)
Notes on Wireless Roaming
Operations Affecting Endpoint Roaming
1. By adjusting the wireless signal strength (adjusting the Coverage value of the management frame) to affect the signal strength, thereby affecting the roaming of the terminal
2. You can adjust the roaming sensitivity of the network card on the terminal (to avoid frequent switching roaming)
Some parameters of the wireless network card can be changed through the advanced properties of the network adapter
Disable Layer 3 Roaming
Ruijie Device Configuration
Roaming local-unroam Turn off layer 3 roaming under local forwarding
Roaming central-unroam Turn off layer 3 roaming under centralized forwarding
No roaming support wlan x Turn off layer 3 roaming between a single Wlan x and other Wlan
Roaming inner-wlan-unroam wlan x Turn off the Layer 3 roaming between a single Wlan x and other Wlans, and turn off the Layer 3 roaming inside the changed Wlan
Precautions
In the case of AC hot standby, STAs cannot roam between ACs of different hot standby instances.
Deploy multiple Wlans, and these Wlans have the same SSID, security authentication and other configurations; if different floors use different Wlans, the STA can also roam between APs on the floors (that is, support the same SSID, different Wlan-id Roaming within AC)