Modem Bridge Mode and Routing

You might find some answers here....

http://www.dslreports.com/faq/westell

What exactly are you trying to do?

Your PC is connected to the DSL modem, and that has a P-to-P connection to the DSLAM, which in turn is connected to an ATM network. Am I right?

I'm guessing that if your DSL modem is in "bridge mode," then it's not routing IP. All it's doing is passing Ethernet frames to the DSLAM, using the physical MAC addresses.

Can you provide more info? Especially, your goal.

The DSL modem connects to the ISP using PPPOE.

QUOTE: I'm guessing that if your DSL modem is in "bridge mode," then it's not routing IP. All it's doing is passing Ethernet frames to the DSLAM, using the physical MAC addresses./UNQUOTE

Well, if that's it, then I can see why I can't connect to the MODEM's http configuration page, because there is no way of getting there.

Goal: I don't know how bridging and to some extent routing works to understand why a computer that say is on 10.10.0.4, the router is at 10.10.0.1. The WAN port of the router connects to the modem whose IP address is 192.168.0.1 (not on the 10.10.0.x) network. The subnet mask is 255.255.255.0 for my 10.10.0.x addresses.

So, it's like why can't an address on the LAN (10.10.0.x) see an address on the WAN of 192.168.1.1)? I was expecting that packets not on 10.10.0.x would get forwarded to the WAN, but 192.168.x.x is not routeable and who/what decides that. Did the router see a request of 192.168.x.x and decide it should stop at the router?

I'm assuming that the router is yours and not the ISP's. If so, how do you have the router, the DSL modem, and your PC physically connected?

Also, if the configuration interface of the router is on the 192.168.0.x network, you're not going to reach it from the 10.0.0.x network. To connect to the router through HTTP for configuration, your PC also has to have an interface on the 192.168.0.x network, and with a matching subnet masks.

Please let me know more about how you have all this physically connected.

Multiple networks and multiple addresses can be assigned on any interface. When the DSL modem is used in bridge mode, it has the 192.168.1.x network bound to it, but none of the other networks. It acts as a repeater in what is called promiscuous mode. This mode listens to all packets and then repeats them all on it's other interface. In this way it acts like a bridge. You can reach it if you use the same network as its interface default. There is webpage on that 192.168.1.x binding.

It will respond only if your PC is also using a 192.168.1.x address. To see this and to see the router through it, you must either change addresses on your PC to match, OR assign a secondary address to your PC. Most system allow you to manually assign secondary addresses. Add the modem address to the hosts list and add the route to it to the routing tables using the modems IP address as the gateway for the 192.168.x.x and 192.168.1.x networks.

This should allow you to see the bridge on 192.168.x.x when you need to, and to see all other traffic through and to the router otherwise.

I'll answer vermin's question first and then come back to Deffburger when I digest some of Deefburger's comments.

1) There is a DSL splitter in the NID

2) 5' away there is a DSL modem

3) About 25' away (Center of the house) there is a Router (An old Apple Snow Router with a bad wireless card). The modem is connected to the LAN port of the router. The Apple router allowed wireless dial-up internet when I had it for free. I might still get free dial-up back.

4) Then there is a 5 port Gigibit switch (free) and another 100bt switch (nearly free).

5) There is an Belkin router ($20) configured as a b/g Wireless access point providing wireless service to the laptop.

6) There is a D-link b/g repeater ($120) somewhere in the house to handle a dead spot.

Printer(wired), Printer(wireless), USB serial server, Slingbox, Roku Radio(wireless) have Static IP addresses. The Laptop have a Dynamic one with a 1 YR Lease.

The OS in use now is Win 7 Pro.

The Telco guy say my DSL service is "pristine". The inside phone wiring is a spider web with lots of quad wire and phone loads.

Perhaps I can clarify further. I can setup my PC and my Intranet (home network) to use 10.1.x.x which is the network number 10.1.x.x with a subnet mask of 255.255.0.0. The subnet mask defines the network number part of the IP address with the 255.255 part. The 0.0 part of the mask defines the host number portion of the address. So all of my IP addresses in my Intranet are set to use 10.1. My Router is one device on my Intranet that links me to the outside world and so is my Gateway. It may also be my DHCP server as well. It will probably be set to 10.1.0.1 as that is the first address in 10.1.x.x network. If my PC is told to go to a network address that is not local, ie on 10.1.x.x, then it will send to the gateway by default. The router, which is connected to other networks and gateways, receives this packet and forwards it to the interface that it's routing tables tell it links to the address you specified.

Now, your modem is bridging. It has an address, but that address is NOT in the routers tables! So your router can't send you to it because it doesn't know that the modem has an address bound to it. YOU do! But when you enter 192.168.1.50 or whatever the modem address is, the router does not have that network in it's list of routes, so it won't send that request through. The reason is simple: The router is bound on it's outside port, it's Internet port, to the Internet address space and it has the Internet gateway(your ISP) as the default gateway. It will try to route your reqest THROUGH the modem, not TO the modem by encapsulating the packet addressed to the Internet gateway address rather than the modems address.

Now, If you connect your PC directly to the DSL modem, and then set your PC to use the same network number of 192.168.x.x and a host number that is not in conflict with the modem itself, say 192.168.1.49, AND you set the gateway on the PC to the adress of the modem as well, THEN you can talk directly to the modem!

The router will not do this unless you set it to use the modem the same way. But if you do, then you can't see the ISP!

All that said, you CAN use multiple addresses and multiple networks on the same wireing, the same Inranet hardware. For instance, you can bind 192.168.1.2 AND 10.1.0.2 to the same ethernet card on your PC. If your printers are setup for 10.1.x.x and your wireless is setup for 192.168.1.x, your PC can see both. If your other PC is set for only 192.168.1.x then it will not see the wireless but it will see the printer. Same is true for your modem and your router.

Many large facilities have divisions within the company network that utilize different network numbers on the same wires and switches. The production machines may be on 10.1 and the office machines on 192.168. The engineers may be setup for both so they can talk to the office systems AND send commands down to the production floor equipment. My servers which run virtual machines may utilize multiple network addresses for similar reasons.

One more thing, answering your question "Can I set the router with a static address to access the modem?" YES. You must use the modems address as the destination AND the gateway for the route to network 192.168.1.0.

source address: 0.0.0.0

destination network: 192.168.1.0

gateway: 192.168.1.? (the IP address of the modem)

That should do ya!

I think I have it for the most part.

Windows Route command has the syntax of:

ROUTE [-f] [-p] [-4|-6] command [destination]

[MASK netmask] [gateway] [METRIC metric] [IF interface]

I know what Metric is, and I should probably use that. It can basically say if you can't find it using what you have look in the other route.

Does Windows Bind on all interfaces if IF is left out? I'm sure I can get what belongs there from ipconfig.

What does a source address of 0.0.0.0 mean?

What should the subnet mask be? 255.255.255.0

or better yet, what should the route command look like?

So, in this case, the gateway would be the address of the router, not the public IP address?

When I was playing long ago, I had this route set, so, I guess it isn't right or is it?

Persistent Routes:
Network Address Netmask Gateway Address Metric

0.0.0.0 0.0.0.0 192.168.1.1 Default

Wireless is 2 and Ethernet is 3 for IF.

Source is used in most routing tables if you are creating or defining static routes. You may not need it. Your command can ignore metric and interface since you probably have only one hop(metric) and only one interface (your ethernet port).

The static route is not for your PC, but is instead an entry in your router, assuming the path from PC to Internet is: PC -> switch -> router -> Modem/bridge -> ISP gateway -> Internet

So, the static route needs to be made at the router. (The switch doesn't care, it moves ALL packets). AND you will need to bind a secondary IP address matching the modem on the WAN interface of the router so the router has an appropriate interface to route through for that network address.

The reason is because the router needs to see the modem directly as a destination not just as a bridge. Your router may be incapable of settings and modifications like these, though some are. I use an old PC for a router running ClearOS and it can be configured for anything.