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jaadu
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extending wifi network to local wired devices

Thu Dec 16, 2021 6:49 pm

Sorry in advance if this is covered elsewhere in another thread. My search attempts didn't find it.

I am trying to use an RB951 to extend a wireless network to a location I can't run a wire for a local wired device. I am hoping to keep the wireless infrastructure (controlled by CAPsMAN) unchanged running in AP mode. I have done the following on the RB951:
- wlan1 on the RB951 is in station-pseudobridge and connected to the wireless network
- ether1-5 and wlan1 are on the same bridge
- dhcp client is running on the bridge and getting an IP from the wireless network

A DHCP address is being offered by the DHCP server on the wireless network to a wired device on the RB951, but it isn't accepting it.
Do I need to pull wlan1 out of the bridge and put the DHCP client on it? Then use DHCP relay to forward the DHCP requests from the bridge to the DHCP server on the wireless network? I need the IP address of the RB951's local device to be on the same subnet as the wireless network.

Thanks in advance,
Al
 
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bpwl
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Re: extending wifi network to local wired devices

Thu Dec 16, 2021 7:35 pm

Station-pseudobridge and DHCP leases is often a problem, with all brands but some do it better.
The problem is that in the D.O.R.A handshake the client D-iscover is OK, but the server O-ffer never reaches the client. So the client never responds with a R-equest.
(The pseudobridge has correctly changed the MAC address in the Discover header, and MT DHCP server is offering to the unchanged MAC address in the DHCP discover. Even while using IP broadcast (L3) the unchanged MAC address is still used (L2). The bridges have no clue on what ports to forward)
Alll devices behind a pseudobridge have a different IP address but the same MAC address. For the DHCP handshake that different IP address is not defined yet.

Workarounds:

1. Some people tried to NAT the L2 broadcast address in the DHCP server Bridge to ff:ff:ff:ff:ff:ff.
2. Using some other brand DHCP server that sends the offer with L2 broadcast.
3 Sometimes just having the DHCP server on another MT helps. The bridge that has to forward the offer to the pseudo bridge, seems to react differently. (flood?)
4. Having an extra DHCP server on the pseudobridge device that distributes leases out of a free subset of the IP range in the same subnet
5. Using static IP addresses in the clients
6. Depart from pseudobridge mode. Use station mode and different NATed subnet for the bridge. (like "Home AP setup")


But I forgot to ask. If AP devices over this wifi link are both Mikrotik, it is ultra simple and stable. Use the "AP-bridge" and "station-bridge" combination. You will have one transparant L2 bridged/switched network. Only works if both are Mikrotik. "CAPsMAN infrastructure" and "RB951" sounds like it is indeed the case.
 
jaadu
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Re: extending wifi network to local wired devices

Thu Dec 16, 2021 11:19 pm

dpwl,

Thanks for the prompt response and the concise explanation of the actual issue! When I read the functional description of station-pseudobridge my gut was telling me the same without the details. :D
All the APs are Mikrotik (wAP AC or hAP AC). Can I infer that using AP-bridge via CAPsMAN will allow standard wifi devices to connect as usual and the RB951 to connect with the needed bridge functionality?

edit: I see that CAPsMAN (ROS 6.49.2) only supports AP mode. I had to manually setup the 2.4GHz radio on a wAP AC and it works.

MANY thanks,
Al

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