The following devices were placed by Telenet at my home:
* Motorola SBV5121E Cable Modem
* D-Link DES1005D Switch (pls correct me if I'm wrong about what this device actually is)
* HD Digicorder DC-AD 2000
From the cable modem an UTP cable goes to the switch (again, correct me). From this switch 3 other UTP cables leave to sevral different rooms. One of those places is my living room. I have 1 UTP connection coming out of the wall there which was used by the HD Digicorder.
Okay. I've got it. Let's start over.
Before you do anything else, put things back this way WITHOUT the DIR-855, and get everything working the way it used to.
You are right, the "switch" is a switch. The manual for the SBV5121E Cable Modem is here http://broadband.motorola.com/consumers/products/SBV5121/downloads/SBV5121_User_Guide_527693-001-a.pdf . Even though the manual does not say it in so many words, the SBV5121E contains a DHCP server and it does network address translation. Therefore, these are things that the DIR-855 have to be configured to NOT do. We will have to run the DIR-855 in "bridge" mode, which is documented in another thread here, but not in the manual.
Magnetron's idea (copying HD Digicorder's MAC address so that router identifies itself with it to my ISP...which I already tried) was...
...wrong. Since the HD Digicorder and the DIR-855 will have to coexist on the same network, they must have DIFFERENT MAC addresses. The MAC address that is identified to your ISP is found on the cable modem.
This was the situation as it was before I decided to place a wireless router. I wanted to have a wifi router because I have laptop (Asus G73) and to use internet on it I connected a long UTP cable on a free port of the earlyer mentioned D-Link switch. My GF and myself grow tired of that darn cable rolled out on the floor to the table where my lappie was on. So I looked into the different available wifi routers and decided to go for the D-Link DIR-855.
Okay. Once everything is back to normal WITHOUT the DIR-855, you need to find out some things about your local network. Follow the instructions in the SBV5121E manual (linked above) to "verify the IP address" of a computer on your network. You need to note the following things:
1) The Subnet Mask, which will be 255.255.255.224. This means that your network contains 32 IP addresses.
2) The Default Gateway. This is the IP address of the SBV5121E. Now, here comes a hard part. On the fourth number of this address, you have to separate the network part from the node part. Express that fourth number in binary. The leftmost three bits (128, 64, 32) are part of the network number. The rightmost five bits (16, 8, 4, 2, 1) are node number. The node number part for the Gateway is probably 1.
Example: The Default Gateway address shown in the manual is 206.19.86.129. The last number is 129. In binary, it is 128+1. The 128 bit is part of the network number. The node number is 1.
3) Now comes the second hard part. All the different devices on you network must have the same network bits, and they must all have different node number bits. There can be no duplicates. 1 is already taken (the SBV5121E) and 0 and 31 have special meanings. (Actually, only one of them does -- but you don't know which.) Try as hard as you can to figure out all the node numbers in use, because you're going to have to pick (guess) a node number for the DIR-855 that is different from all the ones already in use.
The next step is to configure the DIR-855, and you will have to do this OFF of your network. Reset the DIR-855 to get it back to factory configuration. It now has an IP address of 192.168.0.1, which must be changed to something compatible with your network. Make up a small network consisting of a computer and the DIR-855 (on a LAN port), and NOTHING ELSE. You can do this by either connecting the two together with a cross-over Ethernet cable, or you can connect both to the switch using regular Ethernet (UTP) cables, so long as you disconnect everything else from the switch during this step. Temporarily set the computer to a fixed IP address of 192.168.0.2 so that it can talk to the DIR-855. Open a web browser, enter URL 192.168.0.1, configure the DIR-855 to (1) bridge mode (as described in another thread), and (2) under network settings give it addresses appropriate to your network: a "Router IP address" (even though it's not really being used as a router) that is a vacant (unused) IP address on your network; a "Subnet mask" of 255.255.255.224, which is true for your network; a "Default Gateway" of the IP address of your SBV5121E; and a "Primary DNS Address" of the IP address of your SBV5121E. After this is done, and you reboot the DIR-855, it can work on your network. Put the computer back to its normal IP address, put things back to the way they were, and attach the DIR-855 (either LAN port or WAN port) to an unused port on the switch.
This should do what you want. The DIR-855 will pass packets between the wireless side and the wired side, not do anything else.