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Community Member

ADSL with ISDN-backup solution

Dear Sir/Madam,

As a VAR, I have been asked by one of my customers, to search for an internet-access solution which is cheaper than their current solution (but must be reliable as well).

Their current internet connection consist of a 3Com ISDN-dialup router to an ISP which utilizes both B-channels. Workstations connect directly via the router to the internet. This router is also used to have a permanent leased-line connection (frame-relay) to one of their remote facilities. When the bandwidth of this WAN-link drops to a certain minimum value, the connection will be backed up by ISDN-dialup to the remote-facility (which is equiped with the same router).

Since the costs for dialup internet-access is about between $500,- and $700,- a month, the managment asked me to look for a less-costly alternative (on short term). A leased-line is too expensive and isn't fast enough. Here, in the Netherlands, the (telephony)carrier-company KPN is offering a new service called 'MxStream Advanced', which is an ADSL service for internet-access. Monthly costs for this service are about $50,-. The downside of this service is that it isn't reliable enough and does not come with the level of service as you would get with a leased-line. Therefore, I want to offer a solution which uses ADSL and backs up using ISDN when needed (=ADSL connection down).

'MxStream Advanced' will be installed on-site by KPN-engineers. An 'Ethernet modem' (also supplied) can then be connected to a single computer.

What do I have to do to make this work if I would implement this in the company's network? I thought of the following: buy a Cisco 1605R router which is equiped with two ethernet-ports and buy an ISDN WAN Interface Card; connect one ethernet-port to a hub/switch, connect the other ethernet-port to the 'Ethernet modem' (which is like a bridge I guess) and connect the ISDN-port to the NT1. Will this setup actually work??? Is it true that I don't need an ADSL WAN Interface Card when using this 'Ethernet modem'? Can ISDN serve as a backup-connection in the event of DSL-connection failure? Is the Cisco 1605R a good choice? How easy is it to set up this router with the configuration needed, considering the lack of knowledge of Cisco Router configuration? Do you have documentation (or reference) of this specific set up?

I am aware that this setup can be tricky when also having inbound traffic (like VPN, onsite webhosting or mailserver), because the ADSL-connection has a different IP-address then that of the dial-up connection (both static though). But some of these shortcomings can be handled by changing DNS-records and configuring NAT.

If all this actually works, I am certain that we can provide this solution to many other companies.

I would be very thankfull if you can answer these questions. Thanks in advance.

Best regards,

Eddie Palmans

Edit Automatisering, The Netherland

Community Member

Re: ADSL with ISDN-backup solution

What you stated should work and is fairly easy to configure. The only thing I see is what you pointed out and that is that the DSL connection will have different IP's everytime you log on. In America they do offer a business DSL connection that has static Ip's which may be more appropriate for your client, (if offered in your country).

You can do a dial-backup for the DSL through the ISDN using dialer-watch. I'd watch the connection between the router and the ethernet DSL modem. The only problem with that is if the connection between the DSL modem and it's gateway goes down, it will be hard to know it is't down because you can't tell (the LAN side of the DSL modem will still be up).

Community Member

Re: ADSL with ISDN-backup solution


Actually, the IP-address of the ADSL-connection is static as well.

If I would consider using a ADSL Wan Interface Card instead of the second Ethernet port and leave out the 'Ethernet modem', then it should recognize when the ADSL-connection goes down? Am I right? Or: Isn't there a possibility that the router monitors the available bandwidth and decides to use ISDN when certain downstream-values reach a (predefined) minimum value.

Thanks for your input. I really appreciate it.


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