I have an RB751G-2HnD with an active wireless connection as follows.

name="wireless" mtu=1500 mac-address=D4:CA:6D:67:C0:71 arp=enabled
interface-type=Atheros AR92xx mode=ap-bridge ssid="abaca-hidden"
frequency=2412 band=2ghz-b/g/n channel-width=20/40mhz-ht-above
scan-list=default wireless-protocol=802.11 antenna-mode=ant-a
wds-mode=disabled wds-default-bridge=none wds-ignore-ssid=no
bridge-mode=enabled default-authentication=yes default-forwarding=yes
default-ap-tx-limit=0 default-client-tx-limit=0 hide-ssid=no
security-profile=default compression=no

under this interface I have two virtual AP as follows.

name="abaca-secure" mtu=1500 mac-address=D6:CA:6D:67:C0:71 arp=enabled
interface-type=virtual-AP master-interface=wireless
ssid="abaca-secure-dom" wds-mode=disabled wds-default-bridge=none
wds-ignore-ssid=no bridge-mode=enabled default-authentication=yes
default-forwarding=yes default-ap-tx-limit=0 default-client-tx-limit=0
hide-ssid=no security-profile=abaca-secure

name="abaca-guest" mtu=1500 mac-address=D6:CA:6D:67:C0:71 arp=enabled
interface-type=virtual-AP master-interface=wireless
ssid="abaca-guest-dom" wds-mode=disabled wds-default-bridge=none
wds-ignore-ssid=no bridge-mode=enabled default-authentication=yes
default-forwarding=yes default-ap-tx-limit=0 default-client-tx-limit=0
hide-ssid=no security-profile=abaca-guest

I am seeing some very strange results. If I enable each Virtual AP on it's own I can connect to them without any problem, get an IP address and get internet access. They are stable and work perfectly.

However, if I enable both Virtual AP together then I cannot connect to either interface, and only one interface is being shown as advertised to wireless clients, the interface shown is not always the same but only ever one at a time. I have two RB751G-2HnD devices both configured identically and both showing the same problem so I don't believe it's a hardware issue.

I'm running 5.20 but have also tried 6.0 rc1.

Any ideas?

Thanks, Dominic.

I've resolved this problem.

When you create the first Virtual AP it offsets bit 2 of the MAC address of the primary wireless interface to create a unique MAC address for the Virtual AP. It does this each time you create a brand new Virtual AP giving each one an individual MAC address.

However, what I did was open Virtual AP1, use the copy function to create Virtual AP2 and they both then had the same MAC address which is what caused all my problems.

Mikrotik ... perhaps it should warn you if a user tries to create two Virtual AP with the same MAC address given the complications and issues it can cause.

I've resolved this problem. When you create the first Virtual AP it offsets bit 2 of the MAC address of the primary wireless interface to create a unique MAC address for the Virtual AP. It does this each time you create a brand new Virtual AP giving each one an individual MAC address. However, what I did was open Virtual AP1, use the copy function to create Virtual AP2 and they both then had the same MAC address which is what caused all my problems...

I'm wondering if this would explain a problem that I was going to report. Suppose you have a single-radio, single-Ethernet routerboard. Two VAPs (with different SSIDs) are defined on the radio, two VLANs defined on the Ether port, and two bridges, each of which has one of the VAPs and one of the VLANs as ports. So, traffic associated with one SSID winds up going out on one VLAN, and traffic associated with the other SSID goes out on the other VLAN. (At the other end of the Cat5, a second routerboard implements the hotspot interface for one VLAN, and just DHCP for the latter.)

With this configuration, I noticed that the two bridges had the same MAC by default, because they were inheriting not the (different) MAC addresses of the VAPs, but the (same) MAC addresses of the VLANs. However, using the admin-mac setting to give the bridges different addresses didn't seem to help, because I still could not reliably connect to either VAP.

The thing is, in the course of debugging I made sure the VAPs had different MAC addresses. But I'm wondering if the act of "Copy"ing VAPs (which I undoubtedly did) leaves behind some internal identifier that causes a conflict even after the MACs are made different. I'll have to go through the steps again, confirm the problem, then delete one of the VAPs and create it from scratch rather than via "Copy".

Thanks ! I got hit by this same problem ! Wish mikrotik added some Warning of Duplicate MAC Address, or on a COPY, make the MAC all 00:00:00.. so it assigned a new one...

Idem, same problem here...

metal 52 ac - Release 6.38.5

Used copy function in order to add multiple VAPs...
I found the same MAC address.

wlan1 - Office
VLAN10
MAC ADDRESS: xx:xx:xx:xx:xx
Security: Security1
SSID: hide

(VAP) wlan2 - IPCameras
VLAN30
MAC ADDRESS: yy:yy:yy:yy:yy
Security: Security1
SSID: hide

(VAP) wlan3 - Guest
VLAN70
MAC ADDRESS: yy:yy:yy:yy:yy
Security: Security2
SSID: show

Simptoms:
wlan1 - ALL OK, I can connect, navigate, etc...
(VAP1)wlan2 - ALL OK, cameras connect and send/receive packets
(VAP2)wlan3 - Cannot connect with any.... access deneided... "wrong password" (but the password is right!)

I set it to 00:00:00 and It gave me a new MAC address... Tomorrow I'll check if AP started to work.
If it doesn't work I'll try to delete VAPs and do them ex novo without copy option.

Thank You guys!!
Please Mikrotik fix this problem!!

PS: OPS...just reading 6.39 changelog:

" *) wireless - do not allow equal MAC addresses between multiple Virtual APs when same "master-interface" is used; "

thank You Mikrotik! When 6.39 will be more stable I'll switch!

I spent a whole weekend trying to work out why I couldn't connect to one of my SSIDs until I found this post - THANK YOU GUYS!!
The clue was that, when I had two CAP interfaces up and running (master and virtual slave) the master wouldn't connect. When I disabled the virtual slave the master would then work..
I went to the slave CAP Interface and just changed the MAC Address field, hit apply - all fixed!

Arggg… just hit this in CAPsMAN in 6.40.4, took two nights to debug. Glad to find this thread here.

MT, please put the duplicate MAC check in CAPsMAN as well!! Would have saved me a sleepless night lol.