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Author Topic: ZyXEL VMG8924 - Wired port ARP neighbour discovery failure  (Read 312 times)

Iam_TJ

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ZyXEL VMG8924 - Wired port ARP neighbour discovery failure
« on: September 05, 2018, 11:13:56 AM »

I wonder if others could give me some feedback on whether an issue I've recently encountered affects other devices and/or firmware versions or is unique to this unit?

VMG8924-B10A with (currently) V1.00(AAKL.19)C0 in regular routed mode.

I have several devices directly connected to its wired LAN ports. A couple of days ago I found that these devices cannot connect to each other because they cannot discover each other through IPv4 ARP or IPv6 neighbour discovery! The ports are part of the LAN bridge (br0).

What is strange is this only affects wired-to-wired device discovery; discovery and connection from WiFi devices (also on br0 via wl0) works fine (and visa-versa).

Despite extensive diagnosis I've not identified a cause or solution. I'm currently suspecting the Broadcom hardware switch block itself.

More detail:

Using tcpdump on the various devices, and the router itself, I can see ARP who-has (and IPv6 neigh-discover) packets going out on the target device's wired port (e.g. eth0.0), and on the target device I see them received and the ARP/neigh-advert responses sent back. Those replies do not show up on the router (on the source (eth0.0) or target (eth1.0) ports, nor br0) and the target device does not see them either.

As I said, this was working a few days ago.

I discovered this because the target device is running the squid-deb-proxy Debian/Ubuntu package caching server which it advertises via multicast-DNS.

The wired clients can receive the multicast-DNS packets, including from each other, but the connection attempt to the deb-squid-proxy was faiing due to neighbour discovery failing.
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Iam_TJ

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Re: ZyXEL VMG8924 - Wired port ARP neighbour discovery failure
« Reply #1 on: September 08, 2018, 03:53:31 PM »

I wonder if others could give me some feedback on whether an issue I've recently encountered affects other devices and/or firmware versions or is unique to this unit?

VMG8924-B10A with (currently) V1.00(AAKL.19)C0 in regular routed mode.

I have several devices directly connected to its wired LAN ports. A couple of days ago I found that these devices cannot connect to each other because they cannot discover each other through IPv4 ARP or IPv6 neighbour discovery! The ports are part of the LAN bridge (br0).

What is strange is this only affects wired-to-wired device discovery; discovery and connection from WiFi devices (also on br0 via wl0) works fine (and visa-versa).

Despite extensive diagnosis I've not identified a cause or solution. I'm currently suspecting the Broadcom hardware switch block itself.
I tried an upgrade to firmware v24 with no improvement. I've done more detailed testing and it appears the Broadcom Forward Assist Processor (FAP) has failed in some way although there is nothing in the kernel boot messages, or syslog, to indicate anything different compared to the same logs from other devices (I have 3 other identical (8324) devices).

Right now I'm not sure if there's anything can be done about the FAP - I've not even been able to find documentation on it to confirm it gets involved in ARP/neighbour-discovery.
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youngsyp

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Re: ZyXEL VMG8924 - Wired port ARP neighbour discovery failure
« Reply #2 on: October 10, 2018, 10:48:23 AM »

I tried an upgrade to firmware v24 with no improvement. I've done more detailed testing and it appears the Broadcom Forward Assist Processor (FAP) has failed in some way although there is nothing in the kernel boot messages, or syslog, to indicate anything different compared to the same logs from other devices (I have 3 other identical (8324) devices).

Right now I'm not sure if there's anything can be done about the FAP - I've not even been able to find documentation on it to confirm it gets involved in ARP/neighbour-discovery.
This is interesting.

Although my issue is different to yours, it's one that just started to occur, with no apparent change to the 8924's settings. My issue centres around a loss of access to the web, whilst sync remains. I.e. I can't access websites, getting a DNS error message.

No updates in the FW version or level of device reset seem to cure it and as a result, the 8924 is essentially a paperweight. I'm now using a Billion in its place.

I'd be very interested if you manage to solve your issue.

Paul
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