[c-nsp] Multihoming

[Jon Lewis]

On Wed, 15 Sep 2010, Walter Keen wrote:

> Not many options for you I'm afraid.  Some people filter out routes smaller 
> than a /24.  Even if you had a /24 from ISP1, you would then have to get 
> their permission to have ISP2 advertise it.  Most aren't willing to do this.

Huh?  Get a /24 from one of the ISPs.  Get an ASN from ARIN or whoever is 
the appropriate registry for your area.  Advertise (BGP) that /24 to both 
ISPs.  I've never heard of an ISP not allowing this (except that most 
probably won't do BGP with you if you're on a "low end" connection like 
DSL/cable.  If you have some sort of leased line or ethernet connectivity 
to each provider, it shouldn't be an issue.

> Is a micro (/24) allocation from ARIN (if in the US) a possibility?  If so, 
> you could then run BGP to multiple providers and make this a very simple 
> configuration.  If not, you'll likely have to rely on application-layer 
> redundancy.  You can prioritize MX records if you are hosting your mail 
> on-site through ISP1's ip addressing (what you stated seemed a bit unclear), 
> and you could probably do some round-robin DNS entries for web hosting, but 
> it won't be perfect.

Another option might be to get a small amount of space from each provider, 
and VPN into something more stable/better connected.

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