[c-nsp] multihoming solution over two different ISP's

[Jon Lewis]

On Mon, 8 Aug 2011, Aftab Siddiqui wrote:

> Asking for the best solution: Yes its via BGP
> provided that you have you own Public IP space and ASN otherwise its not
> possible with 2 different ISPs. Adding HWIC-2FE would serve the physical
> requirement in your scenario.

BGP is the best way to go, and you certainly can multihome with BGP using 
IP space assigned by one of the ISPs.  Lots of AS's do that.

More below...

> On Mon, Aug 8, 2011 at 2:28 PM, Martin T <m4rtntns at gmail.com> wrote:
>
>> At the moment I have a following setup:
>>
>> http://img69.imageshack.us/img69/4227/252530.png
>>
>> a) Is it somehow possible to automatically switch over to another one
>> connection in case the primary one fails. For example ping
>> www.google.com over a period of time and in case it doesn't respond,
>> automatically switch over to backup connection?
>>
>> b) Is it somehow possible to have one static IP address while using
>> the services of two different IPSs?

You can do "poor man's" multihoming using 2 ISPs (no BGP) by doing 
reachability testing of something or things out on the internet, and 
changing your default gateway when you think the primary connection has 
failed.  You'll have to use NAT/PAT such that when you're going out 
through ISP-A, your outside NAT address is an ISP-A address, and when 
you're going out through ISP-B, your outside NAT address is an ISP-B 
address.  With a bit of policy routing, you can even keep both the ISP-A 
and ISP-B connections up and usable simultaneously.

----------------------------------------------------------------------
  Jon Lewis, MCP :)           |  I route
  Senior Network Engineer     |  therefore you are
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