Inbound traffic suddenly stops

[#1]

@Anonymous 

My Openreach modem is an ECI model which doesn't provide any management interface so I can't see what the sync speed is. Speed tests show no difference in download/upload speeds so I don't think there's much in it.

[#2]

I find it odd that some event on the router causes the modem to sulk … which all seems to be “fixed” by rebooting the router … whilst the router is left in its thought to be sulking state. 

@Townman i have a theory...

@DavidJ AIUI the Vigor 166 provides the ability to access its GUI over the link to the router. To do this the router needs to have suitable configuration e.g a WAN IP Alias and some routing to the local subnet of the modem. Is your router configued to do this?

[#3]

@Townman 

From that I imply that throughout this saga / diagnostic the modem was not reset / had a continuous xDSL session.

Correct. It had a continuous VDSL2 connection. I deliberately did that so that the only changes were to the UDM router.

I find it odd that some event on the router causes the modem to sulk … which all seems to be “fixed” by rebooting the router … whilst the router is left in its thought to be sulking state.

I know, it is definitely very odd indeed, but those are the facts. And the version of the firmware on the UDM definitely has an impact on this. With the older firmware version (3.1.16) everything would be fine until a configuration change is made, at which point the disconnects start. Rebooting the router "fixes" that. With later versions the disconnects can happen straight from a fresh boot and a router reboot doesn't fix it. And remember, swapping out the Vigor/UDM combo for a BT Hub gives a solid connection with no disconnects.

So while the UDM is not at fault, as such, there's something about it that definitely triggers the problem. How, I don't know.

I've been running with the old Openreach modem since Thursday evening and I'll give an update in the next post.

[#4]

@MisterW 

AIUI the Vigor 166 provides the ability to access its GUI over the link to the router. To do this the router needs to have suitable configuration e.g a WAN IP Alias and some routing to the local subnet of the modem. Is your router configued to do this?

The Vigor 166 has it's default 192.168.2.1 address. My UDM is configured with a couple of subnets - 192.168.10.0 and 192.168.20.0 - on separate vlans. I've also given the UDM's wan port the address 192.168.2.3 and set up a static route on the Vigor to route 192.168.10 traffic via 192.168.2.3. That way I can access the Vigor's GUI from my 192.168.10.0 subnet. It's always been that way and I haven't changed that configuration at all.

I have a theory...

I'm all ears!

But have a look at my next post first. I have more information.

[#5]

@MisterW , @Townman 

An update for you.

Since Thursday evening I've been running with the old Openreach modem (the ECI model) in place of the Vigor 166. Since then I've done everything that would trigger the problem but I haven't had one disconnect; it's been rock solid the whole time. I've made numerous configuration changes on the UDM. I've updated the firmware to the latest version. I've rebooted it a couple of times. Nothing has triggered a single reboot.

This morning I put back the Vigor 166 to see what would happen. Bear in mind my UDM is now running the latest firmware which has always triggered the problem in the past. Lo and behold, the disconnects started straight away!

So I think that's fairly conclusive as to the culprit. I don't want to say it's "at fault" because it's also clearly a case of a problem triggered by a combination of the UDM and the Vigor. How that's happening, I don't know.

There are a couple of things I'd like to try with the Vigor before I swap it out again. It gives the options of 2 different "dsl modem codes" which I believe are dsl modem firmware versions. I'll try the other version to see if that makes any difference. Another forum member has also given me a beta Vigor 166 firmware version supplied to him by Draytek. He found that to be much better than the official version. I'll also speak to Draytek to see if they've got any advice or other firmware versions. That will have to be after Easter.

[#6]

Ok, so my theory...

During the PPPoE negotiation, the router will get the MAC address (via the PADI/PADO interchange) for the concentrator. All subsequent outgoing PPPoE ethernet frames will be addressed to this MAC and forwarded by the modem over the DSL PTM link. The Vigor 166, since its gui can be addressed over the same link, must check the MAC address of incoming frames and intercept any destined for its local interface. So where the UDM is configued with the alternate WAN IP (to access the vigor gui) it will (presumably) obtain the MAC address of the vigor itself using ARP.

So if something causes the vigor to mistakenly send what should be PPPoE frames to the local MAC of the vigor, then they will be 'lost' in that the vigor will intercept them as being for its gui but probably just drop them as the contents dont make sense.
If this happens, then data stops going out on the PPPoE connection, and so responses to the DNS requests dry up, the UDM resets the PPPoE connection, starts the PADI interchange and re-gets the MAC address of the concentrator, so everything starts working again!

In reality I suspect a simple modem like the OR one, either doesnt bother to look at the MAC it just forwards everything to the concentrator over the PTM link, or it wont respond to any ARP request for its local MAC anyway, so the UDM doesnt have any alternate MAC to send frames to!.

If the theory holds water, then it SHOULD be possible to see the change in destination MAC on the outgoing traffic when the problem occurs

[#7]

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@DavidJ wrote:

I'll also speak to Draytek to see if they've got any advice or other firmware versions. That will have to be after Easter.

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@DavidJ 

When you speak to DrayTek,  given that they've previously swapped your temperamental 130 for a 166, perhaps ask them to send you a 167 which is otherwise identical to the 166 except that the 167 chipset is allegedly better optimised for FTTC  whereas the 166 is optimised for G.fast copper lines but is quite poor on FTTC.

Out of interest, what are the exact model marking on your 166 and packaging ? for example "Vigor166_Gen2" or "V166-K", etc

and specifically lookout for it showing a region code such as "UK" or "EU", etc.

My 'thought' is that until recently, many of the Vigor 160, 165, 166, and 167 models sold on amazon.co.uk were German/EU imports with English firmware, and were rubbish on BT lines - possibly due to the EU using a different Annex than the UK

I would hope that if you were speaking to DrayTek in the UK, that they would have sent you a UK Annex optimised modem.

These EU imports are a nightmare to navigate if trying to buy second hand on eBay, because unless you know what to look for, then there is a high chance of buying a non-UK modem, from early adopters in England.  The ONLY safe versions to look for are marked with a "K" e.g. "V166-K", "V167-K", etc,  and also some "Gen2" with a "UK" marking on the label.

This Kitz forum topic might be interesting reading - Draytek Vigor 166 G.fast Modem / Router Review 

[#8]

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@DavidJ wrote:

The Vigor 166 has it's default 192.168.2.1 address. My UDM is configured with a couple of subnets - 192.168.10.0 and 192.168.20.0 - on separate vlans. I've also given the UDM's wan port the address 192.168.2.3 and set up a static route on the Vigor to route 192.168.10 traffic via 192.168.2.3. That way I can access the Vigor's GUI from my 192.168.10.0 subnet. It's always been that way and I haven't changed that configuration at all.

@DavidJ   can you confirm that you've got just one ethernet cable plugged in to the Vigor 166 ?

.

[#9]

@MisterW 

Ok, so my theory...

During the PPPoE negotiation, the router will get the MAC address (via the PADI/PADO interchange) for the concentrator. All subsequent outgoing PPPoE ethernet frames will be addressed to this MAC and forwarded by the modem over the DSL PTM link. The Vigor 166, since its gui can be addressed over the same link, must check the MAC address of incoming frames and intercept any destined for its local interface. So where the UDM is configued with the alternate WAN IP (to access the vigor gui) it will (presumably) obtain the MAC address of the vigor itself using ARP.

So if something causes the vigor to mistakenly send what should be PPPoE frames to the local MAC of the vigor, then they will be 'lost' in that the vigor will intercept them as being for its gui but probably just drop them as the contents dont make sense.

Interesting.

I know my Ethernet and IP but I've never had to get into the nuts and bolts of PPPoE. It sounds like you're talking about the destination MAC address that gets stamped into every Ethernet frame. Or are you talking about PPPoE information that's carried within the Ethernet frame?

I've had a look at the capture taken when the problem occurred. This was taken over a short period when everything was fine, then the problem occurred, then the UDM dropped and restarted the PPPoE session, then everything worked fine (for a while). During this time I can only see one destination MAC address stamped into the frames being sent from the UDM to the Vigor. It doesn't change.

[#10]

It sounds like you're talking about the destination MAC address that gets stamped into every Ethernet frame. 

I am.

During this time I can only see one destination MAC address stamped into the frames being sent from the UDM to the Vigor. It doesn't change.

Sounds like that theory is out of the window then...

One thing that might be worth trying ,would be to temporarily remove the WAN IP alias and static  routing on the UDM and see if the problem no longers occurs.

[#11]

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@Anonymous wrote:

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Out of interest, what are the exact model marking on your 166 and packaging ? for example "Vigor166_Gen2" or "V166-K", etc

and specifically lookout for it showing a region code such as "UK" or "EU", etc.

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@Anonymous 

It's a Vigor166_Gen2

The label also says: Applied Area: UK

[#12]

@DavidJ  that's exactly that same version of Vigor 166 that I have, so should be good on Openreach FTTC

[#13]

@MisterW 

Sounds like that theory is out of the window then...

That's a shame. It sounded promising.

I've got the OR modem back in place but when I next connect the Vigor I'll do a capture while accessing the Vigor's GUI, just out of interest and for reference.

One thing that might be worth trying ,would be to temporarily remove the WAN IP alias and static  routing on the UDM and see if the problem no longers occurs.

I can do that. It'll have to wait till after Easter. Making t'internet go up and down over a bank holiday weekend is doing nothing for family harmony and it's obviously all my fault!

[#14]

@DavidJ  can you answer Message 53

[#15]

@Anonymous 

can you answer Message 53

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Oops. Sorry. Missed that one.

@Anonymous wrote:

can you confirm that you've got just one ethernet cable plugged in to the Vigor 166 ?.

Yes, just the single cable between the UDM and the Vigor's P1 port. Nothing plugged into the P2 port.

In looking at the info you asked for from the Vigor, my attention was grabbed by the Factory Reset button. When I next connect the Vigor I may as well factory reset it and reconfigure, not that there's much to configure.