carp on multiple interfaces

HELLO

THIS QUESTION JUST POPPED OUT OF MY HEAD TODAY WHEN PLAYING
AROUND WITH LINUX'S LVS AND KEEPALIVED.

ON A DUAL-CARP SCENARIO ON TWO GATEWAYS WHEN BOTH THE
INTERNAL AND
THE EXTERNAL IFS ARE CARP(4)'D IN A MASTER-SLAVE WAY AND A
LINK
DISCONNECTS ONLY ON ONE SIDE, WOULD THIS TRIGGER A CARP
FAILOVER
OF THE OTHER INTERFACE ALSO?

LIKE IN THE LOCAL SIDE 10.0.0.{1,2} ARE THE IF IPS AND .3 IS
THE
CARP IP, WHEREAS THE 1.2.3.{1,2,3} IPS ARE RESPECTIVELY THE
PUBLIC
IF AND CARP IPS. IF THE LINK ON THE IF OF 1.2.3.1 GOES DOWN,
THEN
THE 1.2.3.3 SHOULD BE FAILED OVER TO THE .2(SLAVE) BOX,
RIGHT?
NOW, ON THE LOCAL SIDE STILL THE .1(MASTER) BOX HAS THE
CARP'D IP
BECAUSE EVERYTHING WORKS FINE IN THE LAN CARP SETUP.
THIS WOULD TURN OUT TO BE A TRICKY SITUATION, BECAUSE THE
LOCAL CLIENTS
WOULD GET NETWORK-UNREACHABLE BECAUSE THE DEFAULT LOCAL
GATEWAY HAD LOST
ITS OUTGOING CONNECTION, AND THE INCOMING CONNECTIONS WOULD
ALSO TIME OUT
BECAUSE THE CLIENTS WOULD SEND THE SYN+ACK REPLIES OVER THE
MASTER BOX,
WHEREAS THAT HAD LOST ITS OUTGOING CONNECTION.

AM I RIGHT THAT THE FREEBSD CARP(4) IMPLEMENTATION HAS THIS
ISSUE?
I DON'T HAVE THE OPPORTUNITY TO TRY THIS AT THE MOMENT, BUT
I'M INTERESTED
IN THE WAY IT WOULD BEHAVE IN A SCENARIO LIKE THIS. HAD
ANYONE MET THIS
ALREADY? ARE THERE ANY WORKAROUNDS/SOLUTIONS FOR THIS?

THANKS IN ADVANCE

SINCERELY,

GERGELY CZUCZY
MAILTO: GERGELY.CZUCZYHARMLESS.HU

-- 
WEENIES TEST. GENIUSES SOLVE PROBLEMS THAT ARISE.

On Tue, Aug 28, 2007 at 11:29:31AM +0200, Gergely CZUCZY
wrote:

> On a dual-carp scenario on two gateways when both the
internal and
> the external IFs are carp(4)'d in a master-slave way
and a link
> disconnects only on one side, would this trigger a carp
failover
> of the other interface also?

See carp(4)

   net.inet.carp.preempt     Allow virtual hosts to preempt
each other.  It
                             is also used to failover carp
interfaces as a
                             group.  When the option is
enabled and one of
                             the carp enabled physical
interfaces goes down,
                             advskew is changed to 240 on
all carp inter-
                             faces.  See also the first
example.  Disabled
                             by default.

i.e. for your scenario you'd set preempt=1 so all interfaces
failover
together, to avoid the problem you describe (which otherwise
would
occur, yes).

Daniel
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THANKS FOR THE ANSWERS. I MUST HAVE MISSED THAT PART OF
CARP(4).

ON TUE, AUG 28, 2007 AT 11:44:29AM +0200, DANIEL HARTMEIER
WROTE:
> ON TUE, AUG 28, 2007 AT 11:29:31AM +0200, GERGELY
CZUCZY WROTE:
> 
> > ON A DUAL-CARP SCENARIO ON TWO GATEWAYS WHEN BOTH
THE INTERNAL AND
> > THE EXTERNAL IFS ARE CARP(4)'D IN A MASTER-SLAVE
WAY AND A LINK
> > DISCONNECTS ONLY ON ONE SIDE, WOULD THIS TRIGGER A
CARP FAILOVER
> > OF THE OTHER INTERFACE ALSO?
> 
> SEE CARP(4)
> 
>    NET.INET.CARP.PREEMPT     ALLOW VIRTUAL HOSTS TO
PREEMPT EACH OTHER.  IT
>                              IS ALSO USED TO FAILOVER
CARP INTERFACES AS A
>                              GROUP.  WHEN THE OPTION IS
ENABLED AND ONE OF
>                              THE CARP ENABLED PHYSICAL
INTERFACES GOES DOWN,
>                              ADVSKEW IS CHANGED TO 240
ON ALL CARP INTER-
>                              FACES.  SEE ALSO THE FIRST
EXAMPLE.  DISABLED
>                              BY DEFAULT.
> 
> I.E. FOR YOUR SCENARIO YOU'D SET PREEMPT=1 SO ALL
INTERFACES FAILOVER
> TOGETHER, TO AVOID THE PROBLEM YOU DESCRIBE (WHICH
OTHERWISE WOULD
> OCCUR, YES).
> 
> DANIEL

SINCERELY,

GERGELY CZUCZY
MAILTO: GERGELY.CZUCZYHARMLESS.HU

-- 
WEENIES TEST. GENIUSES SOLVE PROBLEMS THAT ARISE.