[nycbug-talk] carp

michael lists
Thu Jun 24 09:07:27 EDT 2004

On Wed, 23 Jun 2004 15:33:21 -0400
michael <lists at genoverly.net> wrote:

> I'm reading the OpenBSD man page on carp and I'm unclear 

I checked Ryan McBride's site:  http://www.countersiege.com/ and while
it was an excellent reference, I am still unclear.  It was a Newsforge
article written a few months ago that helped shed some light: 


"CARP requires that the members of a group be on the same physical

Well that was clear.  The kernel trap interview further explains:

"JA: What else is planned for CARP?

Ryan McBride: ... and the ability to configure CARP to use an interface
with an address on a different subnet from the common address, or even
no address at all."

The load balancing question is still murkey to me.. Say I'm making an
http request from my computer at the office to the web server on my home
network.  My office pc will have its Network Address Translated
when the packets leave my floor.  I'm OK with that. 

When that packet reaches my single IP at home, it will cross another
router; the destination address will be translated;  to arrive on the
local network segment.  Here I will (hypothetically) have several web
servers running to handle the load.  But, when the packet hits my carp
virtual IP, it still has the same originating IP from leaving the floor
at my office, right?  But the way I am (mis)reading the man page, it
will all appear to come from the router at home and be balanced to the
same host.

I want to make sure the man page is saying to me... 

"Because CARP uses a hash of the originating IP address to determine
which system to handle the request, all requests coming from all the
computers at your office will look the same to carp and be balanced to
the same host"  

And not  "all reqeusts coming from outside your home router will look
the same to carp".



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