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How to configure my home network to access the Internet and use the FTP server made available by the router

Posted on 2008-10-16
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Last Modified: 2013-12-14
I am in the following (IMHO complex) situation.

I have an ADSL PPPoA Internet connection.
I'm using and Ethernet modem to connect to it.
Then, the modem (which has just an ADSL link port and one Ethernet port) is connected to the WAN port of a router.
Lastly, my PC is connected to one of the router ports.

Let's look at each device.

The Ethernet modem is configured with an IP address of 192.168.2.1, subnet mask 255.255.255.0.
Actually, it is not just an Ethernet modem, but it have many features like routing tables, NAT, firewall, DHCP, etc.: so, it's like a mini-router.
It supports the following ADSL standards: PPPoA, PPPoE, RFC 1483 Bridged, RFC 1483 Routed and Bridged Mode Only.
The first problem is that my ISP dynamically assigns IP addresses, but NOT DNS addresses. That is, when connecting to Internet I have to configure the client so that it obtains IP automatically, but uses two fixed DNS IP addresses. However, my modem seems to mix the two concepts, so either I specify to get all the IP and DNS addresses automatically, or I must specify them all as fixed.
This is not a big problem as long as I then configure the router with the right DNS addresses, but it causes a second problem I will describe later.
For the sake of completeness, this modem is a Linksys AM-200.

The router is configured with an IP address of 192.168.1.1, subnet mask 255.255.255.0. It has all the usual features (firewall, NAT, DHCP, etc.) and it can be configured to access the Internet through its WAN port using PPPoE or PPTP, otherwise it can be configured to use a static IP address in the WAN side or to get IP automatically (so behaving as a DHCP client).
The router also have an USB port to which I can connect a USB hard disk to set up an FTP server.
For the sake of completeness, this router is an Asus WL-500gP V2.

Both the modem and the router have an integrated DDNS client and both support the service I'm using (DynDNS).

What I want to do is:
connect to the Internet from my PC
be able to connect from the Internet (using the DynDNS host name) to the FTP server made available by the router
have a network configuration which can react as fast as possible to perturbations like ADSL disconnections (unfortunately, my ADSL line is quite unstable...)

I'm not a network expert, so I proceeded by trial and error and got two working configurations, but both of them have problems.
They both share the following configuration:
the firewall in the modem is disabled: I'm going to use that of the router
UPnP is enabled on both the modem and the router: I like Windows UPnP support and the ability for certain programs to open ports as they need (eMule, for instance), without forcing me to set up ad-hoc configurations for each of them
DHCP server is enabled in the router for PC clients
NAT is enabled in the router
the modem is configured to use a PPPoA connection, getting IP (and DNS addresses...) automatically from the ISP
the router is configured to use the fixed DNS addresses the ISP gives me

CONFIGURATION #1:
The modem has DHCP server disabled, while the router is configured to use a static IP address of 192.168.2.2. In the modem, NAT is enabled, while DMZ is set to forward all the traffic to 192.168.2.2 (the router).

Problems:
1) I tried to setup the DDNS client in the modem, but while the modem says it's ok, it actually doesn't update the DNS (if I login to DynDNS web site, I always see an old IP address I previously had manually set from there): my suspect is that the modem can't update the IP in DynDNS because it can't resolve the dyndns.org host names, because of the fact I can't set the DNS addresses on it (see above).
2) if I try to use the DDNS client in the router, that seems to work, but it obviously sets the IP to 192.168.2.2, which is the WAN IP seen by the router... and this is not good, of course
3) in this way I'm using two NATs, while I think it's useless; if I try to disable the NAT in the modem, the Internet connection does not work (maybe because I should also set up port forwarding manually from the modem to the router?)
4) I can't understand why whenever I change something in the modem configuration that causes an ADSL disconnection and reconnection, I have to reboot the router in order to have Internet back working; I don't know if this is related to routing tables that need to be updated: after changing the configuration to #2, I discovered that there is an option in the modem to configure it as in Gateway mode or Router mode; the default is Gateway but the on-line help says to use Router if there are other routers in the network and you want to enable the support for the RIP protocol, which sends notifications of network changes; I don't know if this can help (and I don't if I should enable Router mode also in the router, but its manual says that NAT gets disabled then...). Please note that even if Internet connection is not available until I reboot the router, I can always connect to 192.168.2.1 to enter the web management interface of the modem

CONFIGURATION #2:
The modem is configured to use ADSL PPPoA in Half-Bridge mode. DHCP server is enabled in the modem too, while the router is configured to get IP automatically for its WAN port. In the modem, both NAT and DMZ are disabled. In this way the router directly gets the IP coming from the ISP, so that it's internal DDNS client works perfectly and updates the IP address for DynDNS.
The modem is configured in router mode, but I don't know if this makes any difference.

Problems:
1) whenever the ADSL connection is lost, the router gets mad; I think this is because as soon as the modem reconnects, it gets a new IP from the ISP, but the router doesn't realize that and tries to use the old one; in this way I cannot either connect to the Internet, nor to the modem web management interface until I reboot the router; I could minimize the impact of this problem by setting the modem DHCP server lease time to just 1 minute: in this way, the router takes approximately a couple of minutes to automatically react, realizing the IP address of its WAN port has changed and giving me back the Internet connection and the possibility to connect again to the modem using 192.168.2.1

So, configuration #2 is almost perfect, but because of my ADSL line is unstable, about 2 minutes to react to disconnections and reconnections is still annoying.

Further note: although the ISP says to configure my devices to connect using PPPoA, I'm pretty sure it should work with PPPoE, too, because I tried that in the past with other ISPs that use the same network infrastructure. I didn't try it right now, but I will. However, I think that what could make the difference would be the ability to set up the router to estabilish the ADSL connection by itself, so that it can realize immediately when there's a disconnection and reconnection: in other words, the modem should behave just as a plain modem, nothing more. However, I don't know how to properly configure it to do that (maybe Bridged Mode Only as the connection type is the answer? And what about NAT, DHCP and operating mode settings?).

In the end, my whole story translates to the following questions:
1) how to change configuration #1 in order to avoid the double-NATting?
2) why in configuration #1 the router seems not to react to ADSL disconnections/reconnections? The configuration between the router and the modem is always the same (I'm using static IPs), while I would expect that just the modem controls the interface between itself and the Internet, so I shouldn't  have problems at the router level, should I?
3) any idea on how to solve the DDNS client problem in configuration #1?
4) any suggestion for my 2 minutes delay in reaction time I have with configuration #2? Is the use modem just as a modem solution the best answer for this? If so, how to do that?

Thanks in advance to anyone that can help.
Mauro.
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Question by:mauromol
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Expert Comment

by:din101
ID: 22728895
have you tried this ?  disable DHCP on the router and connect modem ethernet port to your routers LAN port (making the router as a switch ) and can you run the dyndns client on the ftp server  or even on your pc.
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Author Comment

by:mauromol
ID: 22728933
Hi din101!
The FTP server is integrated into the router, so the DynDNS client that I should enable is the one of the router, but I doubt it would work if I don't set up any WAN connection on it.
Using the software client on my PC could be another idea, but I would like to have the FTP server working (and accessible from the Internet) even when my PC is shut down (I bought those devices in order to to that).

Thanks anyway.
Mauro.
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Expert Comment

by:din101
ID: 22729043
in that case you need a ip for the router as well (keep dhcp disable). use the lan ports. set the router's ip to be on the same ip range as the modem give out, and put a port fw on the modem to port 21 to come to the routers internal ip. see why dyndns is not working with modem if it's support other servercies like no-ip etc and works why dont you move to that ?
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Author Comment

by:mauromol
ID: 22729112
Thanks again din101!
This sounds like a workaround rather than a solution and I think it wouldn't work in any case because I should make the modem DDNS client to work, but I'm pretty sure it won't (either with DynDNS or with other services) because of the DNS setting problem.

Moreover, I would like to use the router as a router, rather than a switch, so that I won't go mad if in the future I have to change my modem. It would be nice if a modem change would translate to at most a simple WAN interface reconfiguration in the router, rather than to a total network redesign, otherwise I would have bought an all-in-one router/modem/access point device, much simpler to configure.

Moreover, my questions about what is actually going on in my situation are still open.

Thanks anyway.
Mauro.
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Author Comment

by:mauromol
ID: 22738454
Today I made some other tests...

If I configure the modem in Bridge Only Mode and connect it directly to my PC (leaving away the router), I can connect to the Internet using it as a simple modem and by configuring a PPPoE Remote Connection in Windows, without problems. By the way, I have to configure the LAN connection in Windows to use a fixed IP address of 192.168.2.2, because the modem's DHCP server is disabled in Bridge Only Mode...

However, if I place back the router, connect the modem to its WAN port and try to set up the same thing on the router (i.e.: modem in Bridge Only Mode, router configured to use PPPoE to connect to the Internet, using a static IP address of 192.168.2.2), the router keeps on saying there is a PPPoE authentication error, even if username and password are correct. I suspect there's a problem with my router (Asus WL-500gP V2) PPPoE implementation...

Anyway, I fear that, even if I were able to use this configuration, I would still have the DDNS client problem, because I have to configure the router to use a fixed LAN IP address (192.168.2.x)...

Mauro.
0
 

Author Comment

by:mauromol
ID: 22738738
I just read this:
http://www.linksysinfo.org/forums/showthread.php?t=50420
The problem with PPPoE seems to be related to the modem rather than to the router...

Anyway, my doubts remain.

Mauro.
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Accepted Solution

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mauromol earned 0 total points
ID: 22755831
At last, I solved the problem by myself. Actually, I had some issues with my modem (Linksys AM200).

These are the answers:
1) how to change configuration #1 in order to avoid the double-NATting?

I still don't know, but I fear NAT can't be avoided unless the modem is configured as a bridge. This is because in configuration #1 addresses to the public IP must be translated into 192.168.1.x addresses in some way, to get to the router and/or to the PC.

2) why in configuration #1 the router seems not to react to ADSL disconnections/reconnections? The configuration between the router and the modem is always the same (I'm using static IPs), while I would expect that just the modem controls the interface between itself and the Internet, so I shouldn't  have problems at the router level, should I?

This is still strange for me. It sounds like a routing problem, but more tests would be necessary to determine if the problem is at the modem level or at the router level.

3) any idea on how to solve the DDNS client problem in configuration #1?

No. The Linksys AM200 doesn't let you set DNS addresses while configured to get IP dynamically from the ISP. This causes the DDNS client to fail to contact DynDNS website to update the IP associated with my host. I tried to contact the Linksys Technical Support... but I can guess their answer...

4) any suggestion for my 2 minutes delay in reaction time I have with configuration #2? Is the use modem just as a modem solution the best answer for this? If so, how to do that?

This was a subtle problem. It seems that a DHCP lease time of 1 minute on the modem makes the modem and/or the router go crazy. Setting it at 2 minutes solves the problem, although there's still the drawback of the latency between ADSL disconnection and the restoration of the WAN connection by the router.

So, the best solution would actually be to make the PPPoE mode work on the router side, but, as I said in another comment, configuring the modem in Bridge Only Mode and setting up the router to use PPPoE to estabilish the Internet connection is the solution, while there's a PPPoE authentication issue with my Linksys AM200 modem.

A 1.19.04 firmware update exists for the Linksys AM300 that addresses a PPPoE authentication problem and I suspect it's mine! However, no 1.19.04 firmware update is available for the AM200, although I read a notice from an Internet user that says that he successfully flashed the AM300 firmware onto his AM200. I would prefer to avoid to do that unless I'm forced to: meanwhile, I tried to contact Linksys technical support to know if they plan to release a 1.19.04 firmware version for the AM200...

Mauro.
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