What if Multi-SSID mode AP does not work with different VLANs configuration

For TL-WA1201 and TL-WA3001, one of the greatest features is Multi-SSID. Combined with VLAN, it is perfectly suited to provide separate wireless networks for multiple device types and user classes.

However, under certain circumstances, It might not work as we expected.  A typical issue description would be that All mobile devices work well on different SSIDs when 1201 VLANs are all 1. As soon as changing any of the SSIDs to VLAN 2,3,4 etc, they failed to connect and ends up saying "No Internet".

One possible reason we have found is that certain front router does not support VLAN Tagging.

Here we will use the following network topology to explain what happened:

• Process 1: When the phone is trying to connect SSID2 tagged as VLAN 2, it will send the packet to ask for an IP address from the DHCP router.

• Process 2: After the router receives the IP request, it will assign an IP address and send back the packet with a VLAN2 tag (like the following router 1). Then the phone can get a valid IP address and work.

• Process 3: However for the router does not support VLAN, it will ignore the VLAN tag and reply to the IP packet without any VLAN tags(like router 2). When the packets come to TL-WA1201 V3, it will process the non-VLAN data as the default VLAN 1, and forward it to the SSID 1. So Phone 2 in SSID 2 could not receive an IP address from the router in the end.

But there are Access Points in Multi-SSID mode that did work with routers that do not support VLANs.

Under further analysis, we have found that when the data without VLAN is forwarded to certain APs, they would still forward packets to the destination MAC address, despite the VLAN tag. However, we believe the main purpose to set up different VLANs in SSIDs is used to isolate wireless networks, and the VLAN has the priority to restrict devices. The AP should strictly forward data according to VLAN tags, which complies with VLAN requirements and improves device transmission security. 

In this way, if you were having a similar issue on TL-WA1201 or TL-WA3001, Please check whether your main DHCP router supports VLAN Tags or not.