2 NIC's and Proxy Server

Posted on 2000-03-16
Last Modified: 2013-12-19
Part 2 of subdivided question.

>On installation, the TCP/IP  properties wont let me obtain an ip address. (that box is greyed out)... Telstra assigns their ip addresses via a dhcp server on their end, this IP i assume, applies to the cable modem on my end.

this setting shouldn't be in network card properties - but in tcp/ip properties - is this NT we are talking about?

Sorry that was my mistake ... Yes NT is the o/s

My second PDC nic, which is plugged into the cable modem i.e. inside the pdc box, needs an ip address to function within the PDC, so what ip should I be assigning to it ??

|---------|    |----------|
|Cable    |    | PDC      |
|Modem    |----| with     |---(clients)
|         |    |Proxy Svr |
|---------|    |----------|

(I'm sorry  but this ascii diagram is the best i can do under the circumstances If it appears wrong it is simply 2 boxes connected by a dotted line with the word 'clients' in brackets on the end of the second connecting dotted line.)

I was under the impression that it should have the same IP address as the cable modem.

One box (PDC) containing both nic's also Back Office.  ... including Exchange Server, Proxy Server, IIS4 and SQL.

The cable nic should talk to the cable modem (hopefully on the web side of the firewall) and the internal nic serves the clients behind the firewall.

Its a case of one box does the lot.

>umm, i think it would be good if you could describe how you have these different boxes connected to each other - could you draw a simple ascii diagram for us?

done as above

as for addresses, use a private address range, say 192.168.x.x for 'class b' network, or 10.x.x.x for a 'class a' network.

Do you assign an address to BOTH cards ???

As this is only one box with 6 clients, I assume a 'class b' type address is suitable


Brendan Vowles

Here are your options, Bren  
Question by:Bren
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Expert Comment

ID: 2625968's how you should do it.  Set up the NIC on the client side with a static IP in your private address range.  AFTER you do this, set the second NIC to DHCP since the cable modem will be assigning you an address.  You should be able to do this once you have an established static IP on your local network via the other card.  You can test to see whether or not you're getting an address by running ipconfig /all at the command prompt.  

If this is still confusing let me know and I'll elaborate.


Expert Comment

ID: 2626163
Hmm, I don't think you'll be able to get a domain controller to take a DHCP address; it must have a static IP on every network as far as I know.  If I'm wrong I'll be glad to hear it though -- anybody out there make this work?

You may have to ask your cable modem service provider for a static IP, or if they won't give you one, install proxy or firewall on a machine that is not a domain controller.  If your network is small the proxy needn't be a terribly powerful machine and it will still work.

Expert Comment

ID: 2626414
That was kinda my thinking as well...I know you have to obviously set the both as static if you're using it as a router, which basically he is.  If you can get a static IP out of the ISP, more power to ya!:)  A separate proxy server is definitely preferred.
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Expert Comment

by:Tim Holman
ID: 2627410
A PDC will take a DHCP address, its just if the IP address of your PDC changes, clients won't be able to log on until WINS has updated to reflect this change and the local NBT cache of machines trying to log on has had the old entry removed.
ie - not worth it !

I realise you want one box to do the whole lot, but what you NEED is a STATIC address for the cable modem (supplied by your ISP) and a private address range of your choosing for your internal NIC and rest of network.

Proxy 2.0 needs a static IP address for both interfaces, as does Exchange, IIS 4.0, SQL...

Servers NEED static IP addresses !

One box, 6 clients, use whatever IP address scheme you want - 192.168.x.x is fine.

>Do you assign an address to BOTH >cards ???


Expert Comment

ID: 2627886
Proxy 2.0 does not require a static IP however preferrable.  I have done several setups with the ISP side assigning a dynamic address through the cable modem.  Technically, the LAN side wouldn't necessarily have to have a static IP either as long as you were using WINS for your name resolution.  A PDC will not take a dynamic IP if you install only one NIC (I'm still checking to see if it will take it with more than one).  Try it sometime.

Expert Comment

ID: 2628978
Brendan -

Couldn't see all of your question, but it appears like you have a setup very similar to ours.  That is - Server with two NIC's, NIC-1 connects server to modem (SDSL router in my case), NIC-2 connects server to your LAN.  Our server also "does the lot" - Exchange Server 5.5, Proxy Server 2.0.

The way we have it -

Each NIC has a separate IP address.  NIC-1 has address, subnet mask, and default gateway (more in a moment).

NIC-2 has IP address, subnet mask, and default gateway is left blank. is the internally assigned address for our router (your modem).  The ISP maps this within the router to a static IP that it has assigned.

Note, we have 14 clients (you have 6, right?) and I recently set them to static IP addresses and disabled DHCP on our server (we were having some problems with DHCP).  No troubles at all since then.

I hope this helps.

Expert Comment

ID: 2629319
DHCP with the clients is not the issue.  The answer is that you need to either get a static IP from your ISP or set up a separate proxy machine.  Explain the situation to the ISP and I'm sure they'll understand.

Author Comment

ID: 2629435
Thank you everyone for your input. Please be assured that the rejection of this answer is not a dismissal of the answer's content, but a request for more information.


To help clarify my situation for you....

The modem i have indicated is a cable modem connected to the Telstra (phone company who supply cable tv and cable internet access) network. On their end they have a dhcp server so the ip address of the cable modem is not fixed.

With this in mind we have your scenario in place. Now can we foccus in on the [cable modem - NIC-1] aspect of our discussion ?

As I understand it... and please correct me if i am wrong... because we have assigned a fixed ip address to the NIC-1 there is no need to use dhcp for the card looking towards the modem.

What I fail to understand is how NIC1 and the modem can communicate. This may be due to not understanding what the term "gateway" fully means.

You suggested you assigned as default gateway on NIC1. I assume you manually assigned this address to NIC1.

Where I am having difficulty in understanding... is Telstra uses dhcp to assign an ip address to the cable modem .... so what I assign to the "default gateway" address of NIC1 is not static. i.e. it is not under my control.

Mind you ... this may be TOTALLY due to my lack of understanding of the gateway concept.

Please accept my appology if this seems silly to you.

For ease of discussion, I have modified all ip addresses to the 10.0.0.* range in the system I am attempting to configure.

There are other aspects of this question that have now become apparant, but I will wait for your response before i consider weather they are part of this question .... or food for a new one.


Expert Comment

ID: 2632207
Bren, if they are using DHCP on the Telstra side then you HAVE to have DHCP set up on NIC1.  If you set a static IP and then send a request through the modem to Telstra, they're server is gonna say "Who the hell is this guy?" and ignore your requests because you have an invalid IP address.  Therein lies your problem.  You must either find a way to con Telstra out of a static IP, or set up Proxy 2.0 on a server that is not a domain controller and set up the NIC connected to the cable modem for DHCP.  I haven't verified it on my server just yet, but I'm pretty sure you will NOT be able to set NIC1 (or any NIC for that matter) in your server for DHCP because of the role a domain controller plays.

Accepted Solution

alehning earned 100 total points
ID: 2637035
Hm, now I'm confused -- are you saying the cable modem has a separate IP from the one assigned to the NIC connecting to the cable modem?  If that's the case, try setting your server's default gateway to the address of the cable modem.  Clunky but it might work (you'll just have to change it if the DHCP address changes).

However, the way I thought cable modems worked was they connected you to the system, and the computer connected to the cable modem is the one that gets the IP address.  There is an IP that lets you connect from your computer via http and operate the cable modem, but that's not routed or anything.

So -- you will either need a static IP for your *server* (the cable modem is not a node in itself and doesn't have it's *own* IP) from your service provider, or install proxy on a machine that is not a domain controller, I think.

Author Comment

ID: 2639222
Yeah that makes a lot of sence ....The cable modem is not the ip you want to connect to .... it is only the means to aquire the ip of the dns at the other end ... as i understand your comment.

Thanks everyone for your valued input.

Expert Comment

ID: 2640014
Ummm...that's what I said 3 comments before.  Not to be stingy, but I think I should at least get a share of the points.

Expert Comment

ID: 2640031
Ummm...that's what I said 3 comments before.  Not to be stingy, but I think I should at least get a share of the points.

Author Comment

ID: 2640282
To respond to pschwan's comment .... In between your comment and my final adition to this thread, I have done more than enough research.

As I said with my final comment... Thanks to ALL (and this includes you... most definately) for your valued support.

It was necessary to conclude the thead at this point and the final contributer actually confirmed my research ... Your contribution caused me to make the extra research ... and the final contributer summed up my research in a nutshell.

Your response prompted me to do more research as your answer really posed some extra questions to me with regard to the issue.

So the person who concluded the thread, was the person who gave me the most concise answer.

This wouldn't have been possible if the learning curve hadnt been smoothed out by ALL contributions.

I feel under the circumstances, The points were correctly awarded.

Expert Comment

ID: 2678154
Hey Bren just an FYI you can request a static IP address from your ISP (Telstar) Its much more stable in the scenerio that you have presented. you can also purchase the Static IP address if it comes to it...
Also the gateway on the nic connected to your internal network should be the IP assigned to the nic connected to your cable modem. If you assign static IP addresses to the other computers in your internal network the gateway should then become the server nic IP address coneected to your internal network. I have been struggling with this issue for quite awhile now. What I have learned is that the gateway is your router address. The system needs to know the path to the internet. your computer is acting as a router, each nic at a new branch level of your network (tree) needs to know the address of the one above that is piping it to the internet. 1st branch the DNS second the router(gateway)
Then on your side third the nic attached to your server and modem (part of a router) fourth the nic attached to your server and network (the other part of that router) then fifth and finally the hub and client computers. each one of these routed segments must be directed through a gateway.
Kinda late but I hope it will help a little more

Author Comment

ID: 2680265
Thanks for your input .... it is greatly appreciated.

This is a quandry to me too .... and all the help that has been received is most informative.

The structure of Experts exchange, unfortunately, wont allow me to give you any points for your answer.

I feel that everyone has presented me with lots of information that allows me to be a little closer to solving this riddle.

Everyone's help has been of high merit.

Thanks again.

Expert Comment

ID: 2681162
I think the idea of this site is more about an exchange of information and ideas between users and experts then amassing points... Although the structure of this exchange seems to be oriented towards, "He who has the most wins!"
I'm happy that I was able to help as I know in the future I too will be needing help...
Good luck

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