[TriLUG] linux routing example

[Chris Bullock]

Mike Mueller wrote:

>On Wednesday 29 October 2003 12:48, Jason Tower wrote:
>  
>
>>On Wednesday 29 October 2003 12:26, Mike Mueller wrote:
>>    
>>
>>>On Wednesday 29 October 2003 12:05, Jason Tower wrote:
>>>      
>>>
>>>>the catch was,
>>>>they wanted to have zero downtime when they made the DNS changes so
>>>>the web server had to function properly on both T1s simultaneously
>>>>(the two T1s were from different ISPs and had totally different
>>>>subnets).  this is harder than it seems at first glance; in order
>>>>for this to function you have to make sure that traffic "leaves" on
>>>>the same interface it arrived on, regardless of which route is
>>>>preferred.
>>>>        
>>>>
>>>      
>>>
>>even if they were re-routed thru the still active interface, it would
>>probably break the tcp connection since the host at the other end would
>>see a different source IP.  however, this is only conjecture since i
>>have not tried it.
>>    
>>
>
>Tartar Sauce!  This setup is for ISP transition and not high-availability.  
>This setup makes perfect sense for ISP transition.  I was going in the HA 
>direction with my questions. (just found this: http://linux-ha.org/failover/) 
>  
>

We are looking at a similar setup at our office.  We have 2 ISP's, one 
DSL and one T1.  We have dedicated traffic for each ISP, but we want to 
set it up so that if one goes down the router will say "hey, that link 
is down go this way," but we also want to know when the link is back up 
and then normal traffic will resume.  Would we have to look at routing 
protocols ie igrp, etc. or is this feature readily available with Linux 
routing?
chris