[CentOS] High Availability using 2 sites -- the Autonomous System (AS)

Thu Jan 5 19:11:45 UTC 2006
Bryan J. Smith <thebs413 at earthlink.net>

Les Mikesell <lesmikesell at gmail.com> wrote:
> I think they know better than to try to flap BGP routing
> around to accomodate a failed computer at one site or
> another, though.  Is that what you are suggesting? 

Did you even stop to take the *2* paragraphs I wrote into
context?  First paragraph ...

  "Exactomundo.  Even Google has to accomodate such.
   That's why their model is piecemeal and localizes
   as much as they can."

They localize ports of the Internet to localized servers. 
I'm sure it's a 3 or even 4-tier model, where 2 or even
3-tiers are in the same, physical layer-3 space.

If at all possible, you want to minimize flap BGP routing.  I
would NOT suggest you do otherwise.  I'm purposely trying to
point someone in the correct direction on obtaining an ASN
and deploying external BGP, without assuming everyone on this
list as the equivalent understanding of a CCDP or similar.

> BGP would normally be used to handle routing over multiple
> paths to a fixed location and would change in response to
> the route availability.

Again, I'm talking more than just BGP, but an AS number
assigned.  I wasn't trying to get into the entire issue of
internal v. external BGP, but the fact that AS numbers and
BGP interaction between different AS systems is how you
address redundant sites as if coming from the same network.

That's why I said ...

  "But even Google has an ASN, AS15169, when it comes to
   their combined presence."

> You can play tricks by shuffling a route to a completely
> destination if a whole site fails but the minimum you could
> move would be a whole class C at a time, and some bad
> will happen during the switch as different machines with
> old IP's become visible.

Totally missed my points _entirely_!

Sigh, I'm not going to dissect how the Internet works with
ASNs for everyone here to tell you that you're taking my
comments and applying them _incorrectly_.

You can 1-to-1 NAT sites back to another, and that does the
job.  But that also requires you have equipment on the failed
site that can do that.  That's the problem if the site is
taken off-line.

With an ASN, you don't need to localize equipment to do it. 
Damn me for even mentioning BGP, because you seem to have put
your entire focus on BGP as the dynamic routing protocol, and
not the concept of an AS.  ;->

Bryan J. Smith     Professional, Technical Annoyance                      b.j.smith at ieee.org      http://thebs413.blogspot.com
*** Speed doesn't kill, difference in speed does ***