[wplug-bsd] [Fwd: CARP (Common Address Redundancy Protocol)]

[Bill Moran]

There were a few people asking about this, and I just happened to see
this come in off the wire, so I thought I'd pass it on.  It's a high-
availability system first build on OpenBSD.

-------- Original Message --------
Subject: CARP (Common Address Redundancy Protocol)
Date: Wed, 5 Nov 2003 18:50:15 +0100
From: Max Laier <max at love2party.net>
Reply-To: Max Laier <max at love2party.net>
Organization: n/a
To: current at freebsd.org, net at freebsd.org

You might be aware that OpenBSD has introduced a 2-clause BSD-licensed
high availability and load balancing protocol called CARP:
http://marc.theaimsgroup.com/?l=openbsd-misc&m=106642790513590&w=2
http://www.deadly.org/article.php3?sid=20031018101733

I have a working patchset to bring CARP to FreeBSD-Current and would
like to hear you opinon: http://pf4freebsd.love2party.net/carp.html

CARP shows itself as virtual interfaces carpX and works a bit like
vlan interfaces. For comunication between the servers which share a
common address it uses a multicast group.

It supports both IPv4 and IPv6 common addresses and should work on
ETHERNET, FDDI and TOKENRING nets - later two untested, though.

Standing problems:
  - IPv4:
    * Server can't access the common address while MASTER for it.
      OpenBSD has a workaround for this, but we can't add host routes
      with virtual interfaces as gateway, so we need another fix.
  - IPv6:
    * Traffic to the common address on the server is always threated
      locally, even when in BACKUP state.
    * in6_ifattach() will error out - this seems to have no ill
      effects and can easily be fixed by selecting a special if_type
      for CARP interfaces.
  - Locking?!?
  - You tell me!

Tests:
  Very basic tests for IPv4 and IPv6 performed with OpenBSD as a "known
  good" peer. I have very limited test environment at the moment.

Code:
  http://pf4freebsd.love2party.net/carp.diff
  Perforce: branch mlaier_carp

-- 
Best regards,
  Max Laier                    mailto:max at love2party.net

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-- 
Bill Moran
Potential Technologies
http://www.potentialtech.com