Multiple default routes on multihome host

[Tom Judge]

Bill Moran wrote:
> In response to Eygene Ryabinkin <rea-fbsd at codelabs.ru>:
> 
>> Bill,
>>
>> Mon, Feb 18, 2008 at 04:36:18PM -0500, Bill Moran wrote:
>>> I would suggest you ask yourself (and possibly the list) _why_ you think
>>> multiple default routes is necessary ... what is it that you're hoping
>>> to accomplish.  I'm guessing your looking for some sort of redundancy,
>>> in which case something like CARP or RIP is liable to be the correct
>>> solution.
>> I had faced such situation once: I had multihomed host that was
>> running Apache daemon that was announced via two DNS names that
>> were corresponding to two different IPs, going via two different
>> providers.  When the first provider's link goes down, the second
>> provider is still alive, and when both providers are alive, the
>> traffic is balanced via DNS round-robin alias.  Do you see some
>> better way to do it via CARP, RIP, something different?  I am still
>> interested in other possibilities.
> 
> The canonical way to do this is with BGP.  I can be done with CARP
> if both providers support it and are willing to work together.
> 

Unfortunately businesses tend to get bundled PA address space when 
purchasing leased lines off of ISP.  This means that a some what simple 
transition from provider A to provider B can not be done with BGP.  Also 
  as the OP states one the the address blocks that he has is a /25 which 
most ISP's will filter from the BGP address table because it is to small.

I think the cost of learning BGP, getting an AS number and a suitable 
large block of PI address space, getting 2 routers that can do BGP, 
coupled with the consultancy costs charged by the ISP to setup the BGP 
feed totally out way the cost of just multihoming a box for a few 
days/weeks while the required changes take affect..  Ok so this is not 
ideal but hey it works and its simpler..


Just my 2c

Tom