I have a Vigor 2820n routers (in fact I have two here and the problem occurs with both)

The router has been working for a month or so, but recently it sometimes drops off the cable connection and refuses to pick up an IP address generally for the rest of the day!

Watching the status page as I boot up the modem I can see it get a 192.168.100.11 address (presumably from the cable modem (192.168.100.1) but it then fails and drops off after around 20-30secs.

I can use my laptop or desktop and both will connect fine (after powering down the modem for 30 secs) - I can also use a Buffalo WBR2-G54 and a Linksys WRT54G and a couple of other routers and they all seem to work OK, so I'm fairly sure it's the draytek.

I wonder if it's the Virgin Media ssuing the 192.168.100.x address that simply confuses the draytek and that perhaps it then times out.

Has anyone else got any further with this - perhaps it's still a VM issue, but as they won't support anything but a PC it's hard to work though it with them.

I wonder if swapping to NTL:Telewest Business broadband is likely to be any better - anyone have any experience?

Cheers

John A

I have not seen this behaviour but then I am using a Draytek 2600-series router which is not even a cable router and does not have a DHCP client on the (LAN) interface that it uses to talk to the Virgin cable modem.

Here is some information (from a previous post) that I have deduced on the DHCP behaviour of the Virgin cable modem's DHCP server. This is from inspection of how it behaves with a PC (Windows XP) client - I wanted to understand this so I could manually emulate the behaviour for my 2600.

this is what happens after a power cycle of the modem, or an ipconfig /release /renew

First of all a lease is briefly issued in the 192.168.100.x range - this is just a local private address so the device (PC) can talk to the modem. This may disappear so quickly you don't see it.

Then a proper internet address is issued from Virgin/NTL's range, but this is issued on a temporary lease for only one hour.

Lastly, after the one hour lease expires, a 7 day lease is issued.

The good news is you don't have to leave your PC plugged directly into the cable modem for an hour every week. You can force the process with an ipconfig /renew - the 1 hour lease is then replaced with a 7 day lease.

Hopefully that might help to troubleshoot.

I think the reason it issues the short term 192.168.100.* address is to maintain connectivity with the DHCP client (PC or cable router) while the modem is establishing its WAN connection to Virgin and its connection to the upstream DHCP server or PPP server or whatever allocates the public IP addresses.

I wonder if the reason you can't get the public address issued by the modem (after the 192.168.100.* address) is because you have some existing IP conflict or other setup conflict with the address it issues? Just a guess.

Also as mentioned on the other thread, if you are hopping between your PC and your router you need to be sure the MAC addresses of both devices are coerced to be the same, as the virgin cable modem will silently block any device other than the one it issued the first DHCP lease to.

Yep, I'd agree with those observations. I hadn't noticed the 1 hour lease, but it generally doesn't get that far.

The IP address normally given to my router works fine on the laptop (yes I copy the routers mac address to the laptop as I use remote access and regard it as a fixed IP address - I've had it for a year now - Only time it changed was when it was off for a week!) Then once the laptop get the addres, I simply swap the ethernet cable back to the routers WAN2 port - THis simply fools it, as I do it fast enough for the Cable modem not to drop the IP address. It's hardly user friendly and a complete pain - can't really sell one to my clients like this though!!

Raised a call with Draytek - hopefully by providing them with some ethereal traces and syslog info they can fix it or confirm if it's a virgin media issue.
Cheers

John

Sounds tricky. If you jump on the cable modem at http://192.168.100.1/ you can get some additional diagnostics including any DHCP errors. It was all greek to me but might be of use to Draytek, especially since this sounds like it is an error/incompatibility with their DHCP client vs. the DHCP server on the Virgin modem. Best of luck!

I had a look at the specs and manual of the 2820 - a lovely piece of kit, on paper at least.

These are dumb questions, but are you using it with just the cable modem on WAN2, or do you have an ADSL connection (WAN1) as well? Presumably you have not touched any of the many settings relating to WAN2?

Pretty much the 2820 is supposed to do what you are trying to do, so if it won't then as you indicated the best course of action is to raise a ticket with Draytek.

If it's been working for a year then maybe Virgin have changed something in their DHCP server behaviour.

Just to be clear - for the last year the router has been working fine and automatically (using its built in DHCP client on WAN2) - you only started copying the router MAC address to your laptop as a workaround recently, after the router failed to get a DHCP-assigned IP address?

sounds like it is an error/incompatibility with their DHCP client vs. the DHCP server on the Virgin modem

Yes neatly put

I've just sent some traces to Draytek Tech support - there appear to be a large amount of arp requests and also many other DHCP offers - None are the correct ones for my mac address see below:

18 IP-192.168.100.1 IP-192.168.100.10 346 57.194499 DHCP R OFFER 192.168.100.10
19 IP-0.0.0.0 IP Broadcast 346 58.955726 DHCP C DISCOVER 0.0.0.0
20 IP-0.0.0.0 IP Broadcast 594 58.955765 DHCP C DISCOVER
21 IP-192.168.100.1 IP-192.168.100.11 346 58.991649 DHCP R OFFER 192.168.100.11
22 IP-0.0.0.0 IP Broadcast 346 58.991655 DHCP C REQUEST 192.168.100.11
23 IP-192.168.100.1 IP-192.168.100.10 346 58.992985 DHCP R OFFER 192.168.100.10
24 IP-192.168.100.1 IP-192.168.100.11 346 59.994072 DHCP R ACK DHCP Low Lease Time (0 minutes, threshold=30 minutes)
25 IP-0.0.0.0 IP Broadcast 594 00:01:00.992477 DHCP C DISCOVER
26 IP-192.168.100.1 IP-192.168.100.10 346 00:01:00.993788 DHCP R OFFER 192.168.100.10
27 IP-0.0.0.0 IP Broadcast 594 00:01:16.192261 DHCP C DISCOVER
28 IP-10.189.0.1 IP Broadcast 350 00:01:17.403666 DHCP R OFFER 82.33.0.90
29 IP-10.189.0.1 IP Broadcast 346 00:01:17.487495 DHCP R OFFER 10.189.26.236
30 IP-10.189.0.1 IP Broadcast 346 00:01:17.558064 DHCP R OFFER 10.189.7.13
31 IP-0.0.0.0 IP Broadcast 594 00:01:18.193053 DHCP C DISCOVER
32 IP-10.189.0.1 IP Broadcast 456 00:01:19.389805 DHCP R OFFER 10.189.0.128
33 IP-0.0.0.0 IP Broadcast 594 00:01:20.192534 DHCP C DISCOVER
34 IP-192.168.100.11 IP-192.168.100.1 346 00:01:21.249520 DHCP C REQUEST
35 IP-10.189.0.1 IP Broadcast 346 00:01:21.594271 DHCP R OFFER 10.189.26.236
36 IP-10.189.0.1 IP Broadcast 358 00:01:21.660881 DHCP R OFFER 10.233.12.115
37 IP-10.189.0.1 IP Broadcast 346 00:01:24.122264 DHCP R OFFER 10.189.36.32
38 IP-10.189.0.1 IP Broadcast 456 00:01:26.000614 DHCP R OFFER 10.189.16.116
39 IP-10.189.0.1 IP Broadcast 358 00:01:28.403462 DHCP R OFFER 10.221.13.55
40 IP-0.0.0.0 IP Broadcast 346 00:01:28.456701 DHCP C REQUEST
41 IP-10.189.0.1 IP Broadcast 346 00:01:30.826291 DHCP R OFFER 10.189.26.236
42 IP-10.189.0.1 IP Broadcast 456 00:01:30.908815 DHCP R OFFER 10.189.14.226
43 IP-10.189.0.1 IP Broadcast 358 00:01:32.434369 DHCP R OFFER 10.221.13.55
44 IP-10.189.0.1 IP Broadcast 350 00:01:33.391507 DHCP R OFFER 82.33.0.90
45 IP-0.0.0.0 IP Broadcast 594 00:01:35.192654 DHCP C DISCOVER
46 IP-0.0.0.0 IP Broadcast 594 00:01:37.192129 DHCP C DISCOVER
47 IP-0.0.0.0 IP Broadcast 594 00:01:39.191598 DHCP C DISCOVER

Not sure if this would be normal for a cable connection.