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Date:      Thu, 15 Sep 2011 11:07:37 +0200
From:      Damien FLEURIOT <dfleuriot@hi-media.com>
To:        "freebsd-pf@freebsd.org" <freebsd-pf@freebsd.org>
Subject:   CARP interfaces and mastership issue
Message-ID:  <4E71C059.5060404@hi-media.com>

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Hello list,




TLDR: carp interface becomes MASTER for a split second after being
created, even if another MASTER exists on the network with faster
advertisements. Breaks connections. HOWTO prevent ?




We've been experiencing this double mastership problem with CARP interfaces.


Allow me to put some context here:

2 firewalls, PF1, PF2, each with 2 VLANs (for example, some have more)
on a lagg device (link aggregation).
These firewalls then share virtual IPs through CARP interfaces, let us
assume the following:

PF1:
- vlan13
- vlan410
- carp13 (advskew 50)
- carp410 (advskew 50)

PF2:
- vlan13
- vlan410
- carp13 (advskew 100)
- carp410 (advskew 100)

CARP preemption is turned on, so that if vlan13 should fail on PF1, PF2
would assume mastership on both CARP interfaces.
Syscontrols below:
net.inet.carp.allow: 1
net.inet.carp.preempt: 1
net.inet.carp.log: 1
net.inet.carp.arpbalance: 0
net.inet.carp.suppress_preempt: 0


The problem we have is, say for example we reboot PF2.
When it comes back up, it will, even for a split second, assume CARP
mastership for its interfaces, at the same time as PF1.

This breaks existing sessions, openvpn tunnels and new client connections.

While I acknowledge the home-made demons should be built to support tiny
network outages, this doesn't solve our main problem.





We have the same issue when destroying/creating said CARP interfaces.

Recently we upgraded some switches' IOS version on our backup datacenter
(which also has 2 PF boxes, sharing the CARP IPs with the 2 PFs on our
production DC).
To prevent anything nasty happening, we forbade production VLANs on the
switches' uplink ports and only allowed management traffic to allow us
to perform the upgrade.

Things went smoothly but when we brought the production VLANs up again
at layer 2 on the switches, when spanning-tree converged we had again a
double MASTER problem.

I understand I could have avoided it by destroying/recreating the CARP
interfaces, but even in this case there is a split second during which
both firewalls are CARP MASTER.




Is there any way to force CARP to assume INIT state for some time when
coming up, and only after X seconds either become MASTER or BACKUP ?

Any other idea how to solve this, guys ?

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