Dual-Router Oddity

[Piyono]

Greetings from the Holy Land.

So I've been messing with the physical and logical configurations of the routers on the network and found myself stumped by a configuration that looks like it should have worked but did not. The boxes are a DSL modem provided by Bezeq (the telco), a D-Link DVG-1120M for my Primus VoIP service and a WRT54GS v.1 running DD-WRT v23 SP2 standard.

Physical configuration is
[telco] > [modem] > [dlink] > [linksys]

DVG-1120M has an IP of 192.168.15.1
WRT54GS has an IP of 192.168.15.2

I have the WAN port on the Linksys assigned to the switch.

In my second-to latest configuration (call it C1) I had both the D-Link and the Linksys running as DHCP servers in different ranges, the idea being that the wireless machines would take an IP from the WRT54GS. Turns out all the machines, wired or wireless were taking IPs from the D-Link, and that every once in a while they would lose internet connectivity, requiring an ipconfig /renew to restore it. This got annoying so I turned off DHCP in the D-Link (C2). All the machines immediately took new IPs from the Linksys but now, for some reason, they would not connect to the internet, even though they could access both routers. I could get the machines to go online if I set their addresses manually in the TCP/IP properties dialog, but the Linksys, which at this point was acting as a DHCP server, WAP and switch was not passing the DNS and gateway information to the machines.

Here's how DD-WRT was configured on the setup page in C1:
Internet Connection Type: Disabled
Local IP: 192.168.15.2
Subnet Mask: 255.255.255.0
Gateway: 192.168.15.1
Local DNS: 0.0.0.0
WAN port: Assigned to switch
DHCP Type: DHCP Server, Enabled
Start IP: 192.168.15.200
Max Users: 10

Looks like it should have worked with the D-Link in front of it, no?


Where did I go wrong?

Piyono

 

[P5-133XL]

May I suggest the following:

[Telco]->[Modem]->[DLink]->[Linksys]->[Switch]

Here all wired machines plug into Switch. set DHCP for both Dlink and Linksys (each with a different network). This is the optimum setup.

Second alternative:

[Telco]->[modem]->[Linksys]->[DLink]->[Switch]
where all wired computers are plugged into the [switch]. Both the Linksys and the DLink operate as DHCP servers on different networks. All machines plugged into the switch will use the Dlink LAN IP address as their GW and all wireless machines will use the Linksys Lan IP address as their GW. This allows all your wired machines to have VOIP and everything is firewalled by the Linksys, but won't allow your wireless machines VOIP.

Third alternative:
[Telco]->[modem]->[DLink]->[Switch]<-[Linksys]

Here, both the DLink (lan side) and the Linksys (Lan side) will plug into the switch while the Linksys WAN connection is unplugged but make sure its GW address still points to the Dlink. All GW's on all machines will point to the DLink. The Linksys will be the only DHCP server. This will allow all machines, including the wireless, access to VOIP and each other but the firewall will be from the inferior DLink (it only supplies NAT).

You may need to assign static IP's to the telephone lines on the Dlink because I don't know if it will allow the Linksys to supply DHCP for them. If that is not possible, then you can use only the Dlink for DHCP but then I don't know if the Linksys will allow DHCP to cross the wireless link and then you may need to use static IP's for them.

This configuration also may cause problems to internet access for the wireless clients because some routers insist upon sending all GW traffic to the disconnected Wan port regardless of the GW addresses assigned.

 

[ddrueding]

Does your VoiP device need to act as a router? I was able to get mine to act as a client on the network, no routing stuff, just it's own IP and the relevant ports forwarded to it.

 

[Piyono]

Mark, are you suggesting a separate switch in your second configuration? You know that the WRT54GS has a 4-port switch built in, right?

The wired machines don't need or want VoIP. Ideally I'd like nothing more than to have the D-Link box configured as a client on the network with nothing downstream of it other than analog telephones. The UI is a nightmare and I'd like to avoid having to use it at all costs. ddrueding, the box does not have to be configured as a router.

In Toronto I was able to run the VoIP box behind my WRT54GL/DD-WRT with service-based QoS enabled. No problems. Here, well, actually, I haven't tried that configuration, but I did try running the VoIP router behind a Siemens SL2-141 (an all-in-one modem/router/WAP that the telco started handing out as standard issue). It makes an absolute mash of VoIP calls and offers no provisions in firmware for separating the modem/router/WAP functionality so I chucked it and went back to the component modem.

As for all the wireless devices getting IP from the Linksys, how does that work? I had both the D-Link and the Linksys set up as DHCP servers on the same network in different ranges (192.168.15.100-110 for the D-Link, 192.168.15.200-210 for the Linksys) and the Linksys was set as a DHCP server, not a repeater, but for some reason the wireless machines were picking up IPs in the 15.100 range.

Truth be told there is only a handful of computers here and there's no real need for IPs in separate ranges. I just thought it would be cool if I could pull it off. At the end of the day I just want solid Internet and VoIP. The less time I spend mucking about with my own configuration the more time I have to charge people to muck about with theirs.

Piyono

 

[P5-133XL]

Yes, I know the Linksys has a 4-port switch and it is perfectly usable, if it is at the end of the chain. I only really specified the switch because you mentioned a switch in your original configuration so I choose to make it explicit.

Do not use two DHCP servers on the same network: It causes pain (mainly because of different gateways being passed to different machines). As to which server supplies the IP addresses, it will be the one that responds fastest. If the DHCP servers are on seperate networks, it is not a problem because the DHCP protocol packets should be dropped on any router boundary. If the Linksys is both the wireless router and the DHCP server, there should be no issues with wireless machines getting IP addresses. If the DLink is the DHCP server, then make sure that the Linksys does not separately route the wireless machines which is common (and sometimes can be disabled in its setup) and will interfere. It's all easily testable because a machine will either get an IP address or it will not.

 

[Piyono]

Thanks, Mark.

Any idea why the machines couldn't get internet when the D-Link was providing DHCP and the Linksys was acting as a switch and WAP?


Piyono

 

[ddrueding]

Quite often the consumer-level routers will only route data through themselves, regardless of what you set them to.

 

[Piyono]

Quite often the consumer-level routers will only route data through themselves, regardless of what you set them to.

Well, that sucks.
I'll have to find out if that's the case with DD-WRT, although I'd assume such consumer-esque silliness would have been written out, given the power-user appeal of this distribution.

 

[Piyono]

Quite often the consumer-level routers will only route data through themselves, regardless of what you set them to.

Well, that sucks.
I'll have to find out if that's the case with DD-WRT, although I'd assume such consumer-esque silliness would have been written out, given the power-user appeal of this distribution.