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Curious packet loss when connecting my modem to a switch

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MattBoothDev

Occasional Visitor
Hey all.

I have a curious issue when connecting my modem to a switch in order to access the web UI page.

I have a Draytek Vigor 167 (VDSL2 modem/router) which is set in bridge mode and has the IP 192.168.1.1.

I then have an Asus ZenWiFi XT8 router which has the IP 192.168.1.10. This uses PPPoE to authenticate the DSL connection and the router is the gateway for my LAN.

There are two RJ-45 ports on the Draytek modem P1 and P2. P1 is connected to the WAN port on the Asus ZenWiFi and this works as expected, it can authenticate the connection. However, I cannot access the Draytek modem Web UI page to check stats and connection settings.

If I connect the Draytek P2 port to either a TP-Link unmanaged switch (which is, in turn, connected to the switch ports on the Asus) or connect P2 directly into the Asus switch ports, I can access the web UI as expected.

However, if I do this, I get packet loss on the entire connection. Confirmed using the VOIP settings of https://packetlosstest.com, I get around 5% to 30% packet losses. If I remove the aforementioned connection, packet loss is 0%. It's quite consistent.

I'm not a networking expert but nor am I a newbie, but I cannot for the life in me figure this out.
 
If the switch is connected to the router, when you connect the switch to the modem on P2, you may be creating a loop on the ethernet. To configure the modem from P2, just plug in a pc directly or unplug the switch from the router and plug the pc into the switch.
 
If the switch is connected to the router, when you connect the switch to the modem on P2, you may be creating a loop on the ethernet. To configure the modem from P2, just plug in a pc directly or unplug the switch from the router and plug the pc into the switch.
I had suspected the loop issue which is how I managed to diagnose what was happening.

What I'm doing currently is simply connecting it in and out of the switch when I want to check the line speeds, but I wondered if there wasn't something else I could do to stop the loop entirely.
 
Spanning tree. You can configure the flow. But it will be in blocking mode so no access through it.
Spanning tree should have kicked in and stopped your problem. I guess the software does not work on that switch.

You do not want to use cheap switches in large networks as you can take the network down if you plug something in wrong.
 
Don't connect it that way. This is a physical ethernet issue, not a config issue.
I see.

Is it a side effect of using it (the modem) in bridge mode?

Presumably if the Draytek was the router and modem and the Asus was just an access point, I'd likely only need the one ethernet between the two anyway and be able to access the web UI as normal? I did have another Asus DSL modern router before this and used the ZenWiFi as an access point only and could hey into both setups.

I'll keep doing what I'm doing then and only connect when I need to see the stats and potentially grab a cheap PCIe NIC to add to my PC. The software on the Zen is much preferred.
 
When I switched to FTTP I sold my Vigor 166 so this is from memory.
But first off, follow the Vigor manuals, if you follow their setups it will work!
This is the SINGLE cable method: If your Lan is on 192.168.1.x, then using a cable plugged directly into P1 on the modem (with no connection to the router) set the modem to 192.168.2.1 (or on some other similar subnet) and turn DHCP on the modem off.
The Gateway address on the LAN will be the XT8 192.168.1.10 unless you change it to the more common local IP.
Now for the Magic!
XT8 > WAN> Internet Connection
Get WAN IP Automatically: No
IP address: 192.168.2.10 - the IP your router will connect to the modem to access the WebUI
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.2.1

Do that, reboot, and you'll have the modem outside of your LAN subnet, but accessible via 192.168.2.1
*I was doing this for years - it works. Yes you can set things up to use P2 just for the stats without the issues you mentioned, but it's much more work!
 
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When I switched to FTTP I sold my Vigor 166 so this is from memory.
But first off, follow the Vigor manuals, if you follow their setups it will work!
If your Lan is on 192.168.1.x, then using a cable plugged directly into P1 on the modem (with no connection to the router) set the modem to 192.168.2.1 (or on some other similar subnet) and turn DHCP on the modem off.
The Gateway address on the LAN will be the XT8 192.168.1.10 unless you change it to the more common local IP.
Now for the Magic!
XT8 > WAN> Internet Connection
Get WAN IP Automatically: No
IP address: 192.168.2.10 - the IP your router will connect to the modem to access the WebUI
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.2.1

Do that, reboot, and you'll have the modem outside of your LAN subnet, but accessible via 192.168.2.1
*I was doing this for years - it works. Yes you can set things up to use P2 just for the stats without the issues you mentioned, but it's much more work!
Yeah, actually, the default IP of the Draytek is 192.168.2.1 which I did go and change on first setup 🤦‍♂️

The XT8 is indeed on 192.168.1.10 (the other station is 192.168.1.11).

I think DHCP is disabled automatically if you change the operation mode to modem only (rather than modem router) and that is the default mode. The Vigor 167 is marketed as a bridge modem, so probably why that's the default mode.

Thanks for this. I'll have a tinker later and see if I can get that working.

Edit:

With any luck, and if the rep from EE had it right, I might be able to get FTTP within 3 months 😁
 
Setting it up using two cables requires additional settings on the modem, but none on the router. But you still have to set up the modem with a direct connection to some form of computer and not the router, before switching the connections back and hoping for the best. As it's xDSL, and the modem ports are gigabit (IMHO) there's little point in bothering with the 2 cable solution!
*Of course this all goes horribly wrong if your ISP requires that you use those WAN IP settings as part of your setup, but with most UK ISPs you'll get your regular WAN settings through the connection, and this is a secondary setting.
 
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Setting it up using two cables requires additional settings on the modem, but none on the router. But you still have to set up the modem with a direct connection to some form of computer and not the router, before switching the connections back and hoping for the best. As it's xDSL, and the modem ports are gigabit (IMHO) there's little point in bothering with the 2 cable solution!
*Of course this all goes horribly wrong if your ISP requires that you use those WAN IP settings as part of your setup, but with most UK ISPs you'll get your regular WAN settings through the connection, and this is a secondary setting.
I had a go at your suggestion, but it come unstuck a bit :/

In the Asus settings when configuring the WAN IP I also have to provide a Gateway IP. Now, the ones that are automatically picked up are provided by the ISP so not something I could potentially set statically (presumably they will change from time to time).

Thanks for the suggestion, though :)
 
If all those settings auto-populate to anything other than 0.0.0.0 then you probably can't use them. While I did have the modem & router set up and working using two cables for a bit, off the top of my head I can't remember the details of how to achieve it. You do end up with the modem gateway and the control UI 100% isolated from each other - so it's almost like it's two devices.
Good luck, I'm pretty sure I set it up using the instructions from the long downloadable manual on the Draytek site!
 

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