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What changes are needed to let my PC see the cable modem through my router for diagonstics?

192.168.100.1 results in "Not Found". Direct connection from PC to the modem works. Running a Toshiba PCX2200 modem and a WRT54G with WIN2K on 3 PC's.

Thanks.......

Reply to
M2
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Try this first from the command prompt:

route add 192.168.100.1 MASK 255.255.255.255 192.168.0.1 METRIC 1

Reply to
Eff Witt

That's most probably a routing problem...

If your router is set up as dhcp server, it will have an IP like

192.168.1.1 on the LAN side, and your computer will have, e.g., 192.168.1.2.

On the WAN side (i.e., the port that is connected to the CM), it will have the official IP it gets assigned by the ISP's dhcp server. As an example, let's use 100.100.100.100. The default gateway assigned by the ISP might be 100.100.100.1.

So...the router knows that the 192.168.1.0 network is on the LAN side, and that the 100.100.100.0 network is on the WAN side. It also knows that it should send all packets to IPs that are not in these two networks to 100.100.100.1.

Now it gets a packet from your PC (192.168.1.2) to 192.168.100.1. The destination's IP is not one of the two networks it is directly connected to...so it sends it out the WAN port to 100.100.100.1. This is good, since this way it will get to the CM's LAN port. [It will most probably not make it out the CM's WAN port (the cable interface), though, as any sensible ISP blocks packets to private IPs coming in from the LAN side.]

And here's the problem...the packet now still has the IP address

192.168.100.1, but is sent to the gateway's MAC address (this is how packets are sent within the same IP network). The CM *should* not answer to this packet as it only *should* look at the destination MAC address, not at the destination IP, and therefore shouldn't be aware that the packet actually was sent to its IP address.

There are two workarounds for this:

  1. For some reason, the CM actually *does* look at the destination IP, decides it is the correct recipient, and sends the reply back through its LAN port. The router sees the packet is sent to the CPE's IP and forwards it out its LAN port. I would not consider this proper behaviour, but I've seen it...

  1. Your router is able to have a second IP address configured statically on its WAN side. In that case, you can add an IP from the

192.168.100.x range to the WAN side, and you're done - the router will send the packets to the CM's LAN side MAC (since it is in the same network), and the CM will answer to it.

So, I hope that wasn't too complicated...

Regards,

Rolf

Reply to
Rolf Schlömer

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