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S5720HI V200R010C00 Configuration Guide - WLAN-AC

This document describes native AC (hereinafter referred to as WLAN AC) configuration procedures and provides configuration examples.

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Overview of Roaming

Overview of Roaming


WLAN roaming allows a STA to move from an AP to another AP in the same ESS on a WLAN network with nonstop service transmission. In Figure 8-1, the STA moves from AP_1 to AP_2.

Figure 8-1  WLAN roaming networking

WLAN roaming includes roaming between APs in the same service VLAN and roaming between APs in different service VLANs:
  • Roaming between APs in the same service VLAN: APs before and after STA roaming belong to the same service VLAN.
  • Roaming between APs in different service VLANs: APs before and after STA roaming belong to different service VLANs. To prevent services of a user from being interrupted during WLAN roaming, ensure that the service VLAN of the user remains unchanged after the user roams between two APs.

Comparison of WLAN roaming modes

Table 8-1  Comparison of WLAN roaming modes
Roaming Mode Whether the STA Support Is Required Applied Security Policy
Common roaming Not involved All security policies
PMK fast roaming Yes WPA2–802.1X
Roaming Mode Description
Common roaming It is applicable to all scenarios and allows for easy configuration. Services may be interrupted for a short period of time during roaming.
PMK fast roaming It is applicable to a few scenarios. During roaming, users do not need to perform 802.1X authentication again and only need to perform key negotiation. The latency is low.


The biggest advantage of WLAN networks is that a STA can move within a WLAN network regardless of physical media locations. WLAN roaming ensures that a STA moves within a WLAN network without interrupting services. An ESS includes multiple APs. When a STA moves from an AP to another AP, WLAN roaming ensures seamless transition of STA services between APs.

WLAN roaming has the following advantages:
  • Prevents packet loss or service interruption caused by long-term authentication.

    If a STA needs to be authenticated before accessing the Internet, the authentication process (for example, 802.1X authentication) may take a long period of time. Fast roaming prevents STA re-authentication, ensuring nonstop user service transmission.

  • Ensures that users' IP addresses remain unchanged.

    Application protocol packets are transmitted using IP addresses and TCP/UDP connections. STAs' IP addresses must remain unchanged after WLAN roaming so that the TCP/UDP connections established for the STAs are not interrupted.

Updated: 2019-12-28

Document ID: EDOC1000141952

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