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Ive read quite a bit about the issues i currently have with my Aruba WiFi Bridge 501 and the failure of DHCP going through, and as far as i can tell the issue is that the bridge replaces the MAC of the source client in the frame with its own, so that when the recipient replies, it sends the reply to the Bridges MAC, and the bridge has no idea what to do with the reply.

But first, i dont get why they do this - what is the reason? Can they not just forward it without replacing the MAC like switches do (Transparent Bridging)? And second, what can you do against it? The bridge i have is dumb, no CLI, and aside from MAC cloning (which only works for once device), DHCP relay and IP forwarding, it has no settings that could help with this.

So, why do they do that, and what can i do against it?

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    That model is not a transparent bridge – Ron Trunk May 9 at 15:40
  • uh, yes, isnt that exactly what i said? its not transparent which is why i am having these issues – Flying Thunder May 10 at 8:27
  • You cannot have a transparent bridge between ethernet and Wi-Fi. To go from ethernet to Wi-Fi, you need a translating bridge. Ethernet and Wi-Fi frames are very different, so they must be translated between the two protocols. The MAC addressing between the protocols is compatible, so it can be preserved, but the rest of the frame is not at all the same. – Ron Maupin May 10 at 17:51
  • ooh, that makes sense... but what do you mean "the mac can be preserved", i thought non-transparent bridges replace the MAC? which is why DHCP fails? – Flying Thunder May 11 at 16:10
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I had this issue way back in 2015. If it is still the same, there should be an option "Convert Broadcast ARP requests to unicast" which is enabled by default. This option filters all broadcast traffic. Try disabling it.

found the link https://www.arubanetworks.com/techdocs/ArubaOS_81_Web_Help/Content/ArubaFrameStyles/VirtualAPs/Configuring_VAP_Profile.htm

Check the last paragraph of the Convert "Broadcast ARP requests to unicast" section.

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  • Yea, i heard of this option, however as far as i can tell the Aruba WiFi Bridge 501 does not even have a console interface, just a web UI? And in the Web UI this option is not listed anywhere, so i am assuming the device i have is a bare-minimum that just doesnt work in this setup – Flying Thunder May 10 at 9:21
  • ok, one last thing. Did you try disabling the "act like dhcp relay agent" under "frame processing" menu? – kaya atabey May 10 at 9:47
  • no, i enabled it from the beginning because it sounded like its what i needed, but to my suprise it didnt seem to be doing anything - do you think disabling it would actually work better? – Flying Thunder May 10 at 10:59
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WAPs ("they") in general don't work like that. If your device does so it's most likely configured wrong. You seem to want "transparent bridging", that leaves all MACs intact when forwarding.

The 501 seems to be a client bridge, so you need to make sure that its upstream WAP is also configured correctly. If you need to verify the configs you need to add them to your question (sanitize sensitive information before).

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  • so WAPs in general dont replace MAC adresses? because i read countless of posts online where people had the same issue of DHCP failure with wifi bridges, and the common census seemed to be that it is because of this behaviour – Flying Thunder May 10 at 8:28

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