DSL "AND" Cable Broadband

Posted on 2007-07-21
Medium Priority
Last Modified: 2010-03-17
Right now I'm using Comcast/Formerly Adelphia cable and have to say I've had pretty good service. I also keep a $10 a month dial-up account with Bell South (ATT) that I use on the rare occasion Adelphia/Comcast went out. Also works when I'm out with a customer who can't connect and I'll use the dialup as a test. And other uses.
Just the other day, however, I lost the broadband sig and had to put up with the BS dialup for 4 days.
There is a special BellSouth DSL offer that they were required to put out for $10 and I wondered if there was any reason why I couldn't have the DSL sitting there for use when the cable goes out.
It would also continue to give me the dialup BU since that's included with all their DSL.

Here's the link and I have one customer who actually got it for the $10. Swithched from Earthlink dial-up to this.
Question by:cfourkays
LVL 13

Accepted Solution

dhoffman_98 earned 500 total points
ID: 19538715
There's no reason you can't do this. You just can't have both gateways on the same network running at the same time because you can only have one default gateway. If the idea is to have automatic redundancy, then you would need to install a router that has two external interfaces and one internal interface. Your internal machines would connect to the LAN side, and then the modems for your cable and DSL would be connected to the two WAN interfaces. The router would then be configured with routes that point all outbound traffic to both WAN interfaces, but you would select a priority metric value for the preferred one to be lower than the backup one. If the preferred one is unavailable, you would automatically switch to the other.

However, you then run into issues with DNS. If your internal client machines are using the DNS servers at your ISPs, then you would have to reconfigure them as well unless the router could also be configured as a DNS proxy that would also automatically reroute the DNS queries to the proper path.

If automatic redundancy is not a necessity, you can have the DSL line there as a backup, with it's own modem/gateway/router, and when you need to use it, you can unplug your internal network from the cable router and plug it into the DSL. You'll then have to reset your DHCP settings to point to the other router (unless you happened to give them both the same IP Address), and you would have to update your DNS settings to point DNS queries to the alternate provider.

There are also freely available DNS servers on the Internet that you can use. They are open to accept queries from anyone. If your clients are configured to talk to them, then you won't have to switch DNS settings when you fail over and fail back.

Author Comment

ID: 19539953
Thanks, hoff
I even went ahead and ordered the ATT/Bellsouth DSL LIte for $10.
So now I have Comcast cable , (super fast, but lousy line tech service, great phone service but expect days for house calls,), with a combined DSL Lite/Dialup package for backup and testing.
I use a Buffalo router so I'll just leave the modems along side each other.

Couldn't beat that $10 deal.


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