CARP interfaces and mastership issue

[Damien Fleuriot]

On 9/15/11 11:07 AM, Damien FLEURIOT wrote:
> 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 ?
> 
> 
> 
> _______________________________________________
> freebsd-pf at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-pf
> To unsubscribe, send any mail to "freebsd-pf-unsubscribe at freebsd.org"




Hello List,



This is a follow-up to my original email quoted above.




It seems that there is an existing bug in OpenBSD 3.8 and lower's CARP
implementation which causes CARP interfaces to skip the INIT state
altogether and start as MASTER if preempt is enabled.

Source:
https://calomel.org/pf_carp.html

Quote:
INIT : All CARP interfaces start in this state. Also, when a CARP
interface is admin down, i.e. "ifconfig em0 down", it is put into this
state. When a CARP interface is admin up, it immediately transitions to
BACKUP. Note that in OpenBSD 3.8 and earlier, a bug exists which will
cause the host to transition to MASTER right away if preempt is enabled.


I have been able to verify and reproduce this behavior on boxes running
both 8.1 and 8.2 FreeBSD.




Does anyone know what version of OpenBSD's CARP implementation we're
running on FreeBSD 8.x ?

It seems like this is the same bug, to me.