[Gloucs] Routing woes

[Glyn Davies]

Dave Addison wrote:
> In message <A39E8A01D422D611A45B0090276AFAD81CF266@comsrv>, Tim Ballam 
> <Tim.Ballam@cpccomputers.co.uk> writes
> 
>> Routing woes
>>
>> I'm trying to set-up a network with a DSL and cable modem connection and
>> want the cable modem to be the backup.  If I set a workstation up with 2
>> default gateways and start a ping going if I pull the DSL network cable I
>> get no network access until I delete the offending gateway.
>>
>> Anyone any thoughts. (apart from spending about 5K on a box)
>>
> I think you need to be running either gated or routed to dynamically add 
> and delete entries from the routing table dependent on what routes are 
> being advertised by the attached boxes. This does depend on the DSL and 
> cable hardware supporting the protocols.
> 
> Personally I've got about as far as you have before giving up. Only in 
> my case the machine went down when I was 40 miles away and that was when 
> I found out having two identical entries in the routing table didn't work.

Hmmmm. I've never done this myself but here are a few things to think about.

I guess you need to make your 2nd gateway appear more 'expensive' than 
the first. That way you will always use the DSL link if its available. 
Then, you need a way of determining that your primary gateway has gone 
down (suddenly become uber expensive). Hmmmm. I guess you are going to 
be needing to run routed and listening to RIP packets or one of the 
later protocols. Only thing is I don't know whether ISPs send RIP down 
the wire (tcpdump/etherreal should tell you). If not, I'm not sure how 
you are going to detect your link has gone down. You are left with using 
static routes which is entirely what you don't need.

Suppose you could run a script from cron to test if your primary gateway 
is available and ammend your static routes as needs be. Yep, I majored 
in kludging at college (slacking minor).

I'll be surprised if Google can't answer this too?

-- 
Best Regards
Glyn Davies