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FS#3155 - Asus RT-AC85P missing incoming packets; switch misconfiguration? #6345

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openwrt-bot opened this issue Jun 7, 2020 · 3 comments
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dwmw2:

I installed an Asus RT-AC85P with current master (2020-06-05 around commit 8c31afb)

It is connected to the house network via its 'wan' port.

Wireless clients which have recently been associated with a different access point in the house cannot see DHCP responses.

A tcpdump on the 'wan' interface shows the request going out, but no reply.

This happens when the DHCP server is connected directly by a wire to the WAN port of the RT-AC85P, and when tcpdump
on the DHCP server says it is sending the reply. Putting the upstream switch back in the path as normal and using port mirroring confirms that the DHCP server isn't lying (it's a BT Home Hub 5a with its own internal switch which I briefly suspected of being involved).

Using tcpdump on the 'eth0' interface of the RT-AC85P seems to show that the DHCP reply isn't being seen there either. Although those packets are hard to deal with as they aren't proper 802.1Q.

I plugged a USB Ethernet device into the RT-AC85P and connected it to the house network through that instead. Now it sees the DHCP replies and roaming wireless clients work fine.

Clients which haven't recently roamed from an AP elsewhere on the house network are fine. It seems like the internal switch of the RT-AC85P is learning that they are on the wired network, and not delivering their packets to the CPU?

When a wireless client associates and attempts DHCP, tcpdump on the 'wan' interface shows the

Supply the following if possible:

  • Device problem occurs on
  • Software versions of OpenWrt/LEDE release, packages, etc.
  • Steps to reproduce
@openwrt-bot
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dwmw2:

Using lan ports of the switch makes no difference to the behaviour.

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dwmw2:

Looks like the box is actually running r13489-5aa2ddd0d6 and the fix from https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5e5502e012b8129e11be616acb0f9c34bc8f8adb has already been merged.

Will update and test...

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dwmw2:

Yes, that appears to fix it

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