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Router has 3 MAC addresses?


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#1 MaryBet82

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Posted 18 May 2010 - 09:29 AM

I'm trying to help my sister reestablish her wireless connection to her Linksys WRT54G wireless router after her ISP switched her to a DOCSIS 2 modem and I'm pretty confused at this point. She has a strong wireless signal, but can't connect to her router or the internet. I have been able to connect to her SSID w/ my thinkpad in the past, but I can't get a connection wirelessly now either.

I connected my thinkpad via Ethernet cable to her router to get into the router's browser pages so we could write down the settings before hitting the reset button. I expected to find a MAC for the router and a Mac for the wireless part, but there were 3 MACs listed - one for "Router", one for "Local Network" and one for "Wireless". I'm guessing that the "Router" MAC is the "outside" MAC that assigns itself the IP assigned by her ISP and the "Local Network" MAC is assigned an "inside" IP by the router's NAT function. Is that correct? Is that part of the firewall function - to have two MACs? I thought maybe that "Router" MAC was actually the modem's MAC but it only differs by one character from the router's "Local Network" MAC so I think it's actually the Linksys' MAC.

I was also confused that the "Router" MAC had a Default Gateway IP address on its Status page that differs by the last 2 set of numbers from the listed "Router" IP address. I thought an ISP would assign one IP address to the connection and that the router would - I forget the term - sort of copy it onto itself from the modem. I thought the Default Gateway = the router but was an inside the LAN term and that the Default Gateway's address would equal the internal IP address the router assigns itself - like 198.162.1.100.

I found a lot of different possible solutions to try when I googled DOCSIS 2 + linksys wrt54g, so I'd like to get a clear idea of what's what so we can use some logic in our troubleshooting efforts - before we haul her desktop & monitor close enough to connect via Ethernet to the router.

Can someone explain these MACs & IPs to me in terms of an ISP-modem-router-firewall-NAT connection?
mac 10.6 on macbook pro
WinXP sp2 on Dell 380 w/ 512 MB RAM- currently dead in the water
WinXP tab ed sp 3 on Thinkpad X41 w/ 1.5 GB RAM - lemony flavored
Win2K Sp4 on Sony VAIO GXR600 w/ 512 MB RAM - currently blue screening

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#2 Baltboy

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Posted 18 May 2010 - 11:21 AM

Don't worry about the MAC addresses. IT is a unique number hard coded into every network adapter in existance. Think of MAC addresses like a street address, it simply is what it is and you cannot change it without moving(or in the network case using a different network card). Mac addresses are part of the data link layer which is used by switches and other appliances that function at the second layer of the OSI model. Switches match up the IP address of a computer with it's MAC address at the switch to send the data to the approriate port. IP addresses are logical identifiers used to connect over a TCP/IP network which is what your router and the internet use. On a TCP/IP network IP addresses are used to route data packets from the source (like your computer) to a destination (like this website) and back to the source. They can be changed but require a unique IP address for each network attached item. Finally we get to NAT since there are physically more network attached items in the world then there are IP address (in V4 at least) a solution had to be created. NAT stands for Network Address Translation. The computer world loves its acronyms. It allows you to have one unique IP address (usually located at the router) to access the internet and a set of private IP addresses that are only for your network. NAt takes the data packet from your computer and encapsalates it so it can be routed on the internet. So.....

ISP(provides unique IP address)-modem(facilites communication over type of connection)-router(receives unique address, provides NAT functionality, may contain switching as well)-firewall(scans data packets to verify source and destination tampering, blocks ports from outside access)- Nat Connection(really part of the router functioning to route data over the internet using a private lan setup for the internal IP structure)

So you should be seeing three MAC addresses on the router one for the local NIC you are attached to, one for the WAN port on the router, and one for the wireless NIC. The fact that she changed to docsis should make little difference to the router. Check the settings for the router to be sure it is using DHCP to obtain an address from the modem or enter the Satic IP information provided by the ISP if provided. Then unplug the router for 30 secondsand plug it back in. Do not turn it off with a switch it must be unplugged. Plug it back in and re-attempt to connect using both wired and wireless settings. You should also do an ipconfig /release then ipconfig/renew from a command line window to reset any setting in the computers which may have changed since resetting the router.

Also what is the model and make of the docsis modem? More and more of the newer modems include the functions of a basic router which need to be disabled when using your own router.
Get your facts first, then you can distort them as you please.
Mark Twain

#3 MaryBet82

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Posted 19 May 2010 - 01:08 PM

Thanks Baltboy,

I did the ipconfig /release and ipconfig /flushdns yesterday and connected to both her router browser pages and the internet via ethernet w/ my thinkpad and later the internet via my wireless. Since I can access the internet via wireless and ethernet w/ my thinkpad thru her router, the problem isn't w/ the new modem + her router.

She has a CISCO 2100 cable modem and I'm 99.999% sure it doesn't have any router functions. The info & CD that came w/ the modem only had instructions for connecting to the ISP for the first time and for changing VOIP setup, so I figured she just needed to do the computer off, router off, plug modem in, wait for all the lights, plug router in, wait for all the lights, turn on computer. I was wrong.

She did the unplug router bit initially several times w/ no luck. The ISP did fix something on their end when I called for help, but it didn't fix things on her end.

We can try unplugging the router bit on her computer again today along w/ the ipconfig /release. She may have some 3rd party software causing a problem, but we haven't found any yet. Even tho she has a linksys pci wireless adapter [winxp] we didn't find any linksys adapter program like I have w/ my linksys wireless pc card [win2k], so her wireless appears to be managed by windxp's zero wireless configuration service.

I never knew home routers had both a WAN port MAC and a local NIC MAC, tho I guessed they had a wireless MAC when that function got added. Other than the wireless MAC, I thought they had the one MAC listed on the bottom of the router. I like to know as best I can what's going on so I know what numbers to put where when I have to do some manual configuring or to spot when the setting or number has been autoconfigured incorrectly.
mac 10.6 on macbook pro
WinXP sp2 on Dell 380 w/ 512 MB RAM- currently dead in the water
WinXP tab ed sp 3 on Thinkpad X41 w/ 1.5 GB RAM - lemony flavored
Win2K Sp4 on Sony VAIO GXR600 w/ 512 MB RAM - currently blue screening

#4 Baltboy

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Posted 21 May 2010 - 08:08 AM

Just to clairify something every network adapter has its own MAC address so the if the router has four LAN ports, one WAN port and Wireless it has six MAC addresses. You never need to know any of them unless you are filters by MAC address.

As far as the wireless goes I would start from scratch by resetting the router to its default and then trying to connect. This eliminates the possiblity of misconfigured secui=rity and such. Then once you have established a connection set up the wireless security again.

After looking at the router it does have built in router functionality. They call for it to be connected to a hub. YUK!!! Modems with this kind of functionality can cause all kinds of stupid problems on a dedicated router set up. Usually what I see it random internet connection losses that stem from multiple DHCP servers functioning on the same network. Anyhow most of these so called modems can be accessed in the following way. Connect directly to the modem from the computer using a wired ethernet connection using DHCP. Do an ipconfig /all and write down the default gateway that should be the modem/router address. Open IE and enter the addess in the bar. A username password window should pop up. Now here is the tricky part since I can't find anything on the default setup. Usually it is one of a few things.

1. username: leave blank password:admin
2. username: admin password:1234 or 12345
3. password: Admin password:guest

Once your in then you need to change a few things in order to get things straight. Unfortunately I haven't worked on the particular model before so you will have to interpert and locate the specific things yourself. First there will be a setting for DHCP. This needs to be turned off. Apply the settings before leaving the page or they will not stick. Second somewhere there will be a setting describing the function being provided. It will usually say router or something to that effect. This needs to be changed to bridge. Once again apply the settings. Finally change the IP address to something on the new router subnet so you can get back to if need be. If you are using a linksys or cisco router than set it to 192.168.1.3. Now disconnect the computer and hook up to the powered down router and fire it up. Everything should work better now. Hope all this helps.
Get your facts first, then you can distort them as you please.
Mark Twain




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