WLAN roaming

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WLAN roaming allows STAs to move within the coverage areas of APs belonging to the same ESS with nonstop service transmission.

The most obvious advantage of WLAN networks is that a STA can move within a WLAN network without physical media restrictions. WLAN roaming allows STAs to move within a WLAN network without service interruption. An ESS includes multiple APs. When a STA moves from an AP to another, WLAN roaming ensures seamless transition of STA services between APs.

WLAN roaming has the following advantages:

- Retains STAs' IP addresses. After roaming, STAs can still access the initially associated WLAN network and retain their services.

- Avoids packet loss or service interruption caused by long-term authentication.

Other related questions:
Which WLAN devices support roaming
Fat APs do not support WLAN roaming. AC+Fit AP networking support WLAN roaming. V200R003 and earlier versions support only intra-AC roaming, while V200R005 and later versions support both intra-AC and inter-AC roaming. Depending on whether a STA roams within the same subnet, WLAN roaming is categorized as Layer 2 roaming (on the same subnet) and Layer 3 roaming (on different subnets). Layer 2 roaming is classified into fast roaming and non-fast roaming according to security policies used by STAs. Only when the security policy is WPA2-802.1x and STAs support fast roaming technology, fast roaming can be achieved.

What is the roaming mechanism of APs
A roaming process is initiated by the STA. A STA may roam when it detects signals of a new AP which are stronger than that of its currently associated AP. A larger signal strength difference indicates a higher roaming possibility. Roaming aggressiveness of STAs varies. Some STAs support manual configurations of roaming aggressiveness on NICs.

How to configure roaming on an AC
By default, the AC supports intra-AC roaming, which can be implemented as long as the basic WLAN services are configured and the source and destination APs have the same SSID and security policy. To implement inter-AC roaming, you need to configure the master controller, mobility group, and home agent. Note the following points when configuring WLAN roaming: 1. Two APs must use the same SSID and security profile. 2. In the direct forwarding mode, services of a roaming user may be interrupted for a short period because ARP entries of the access device connected to an AP do not age in time. To prevent this problem, run the learn client ip-address enable command in the VAP profile view on the AC to enable STA IP address learning. This function enablesAPs to promptly send gratuitous ARP packets to the access device for ARP entry updates, so that user services will not be interrupted during roaming. By default, STA IP address learning is enabled. 3. A maximum of 16 ACs can be added to a mobility group. An AC can be added only to one mobility group. 4. ACs in the same mobility group must use the same software version, otherwise inter-AC roaming may fail. 5. In dual-link hot standby (HSB) scenarios, roaming between active and standby ACs is not supported. Service interruption may occur if users roam in this scenario.

How to display the roaming trace on an AC
After STA roaming, run the display station roam-track command to on the AC to display the roaming trace of the STA.

When a STA is roaming, whether the STA subnet attributes are changed
During STA roaming, STA subnet attributes such as the IP address, VLAN, ACL, and priority are inherited and will not be changed.

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