[nsp] Is default failover in dual-homed DSL possible?

[Furnish, Trever G]

Can you configure the DSL modems to drop the router side of the connection
when the ISP side drops?

Are the "modems" themselves capable of running a routing protocol with your
router?  Some of them are - but most aren't. :-)

> -----Original Message-----
> From: Mark Boolootian [mailto:booloo@ucsc.edu]
> Sent: Monday, December 16, 2002 7:24 PM
> To: cisco-nsp@puck.nether.net
> Subject: [nsp] Is default failover in dual-homed DSL possible?
> 
> 
> 
> Folks,
> 
> I'm looking for a solution for home/business DSL users who 
> want dual-homed 
> DSL connections to protect against outages.  The basic 
> picture looks like
> this:
> 
> 
>        ----------         -----------
>        |  ISP 1 |         |  ISP 2  |
>        ----------         -----------
>            |                    |
>            |                    |
>            |                    |
>           -----               -----
>           |   |               |   |  <- DSL modems
>           -----               -----
>              \               / 
>              ----------------
>              |   router     |
>              ----------------
>                     |
>                     |
>             --------------------
> 
> The router is doing NAT, and there is no dynamic routing 
> protocol running
> between the router and the ISPs (i.e. typical home DSL 
> setup).  The question
> is, are there any products/mechanisms for allowing a static 
> default pointing
> at one ISP to failover to the other ISP in the event of a 
> network outage
> at the first ISP?
> 
> In the above diagram, a failure with DSL would take down the 
> PPP connection,
> so presumably if the DSL modem were built-in to the router, 
> the router would
> notice that the PPP connection was down, and perhaps the 
> right thing could be 
> made to happen.  Unfortunately, I don't know of a small 
> router that would 
> accommodate this solution.  I suppose if one were to 
> terminate each DSL 
> connection in an individual router, and then feed both those 
> connections into 
> a third router, one might be able to manufacture something 
> that would work, 
> but I don't think I'd want to put that on my resume (much 
> less mention it on 
> this list).
> 
> In order to accomodate failures beyond a dead DSL link, I've 
> got a rather 
> messy idea in my head of a box sitting on the LAN pinging 
> nameservers in each 
> of the ISP's networks, and making routing changes on the 
> router accordingly.  
> 
> Has anyone on this list set up anything to deal with such a situation?
> 
> Thanks very much,
> mb
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