Lots of vrrp (carp?) packets outbound from WAN



  • Our isp told me they're seeing a ton of broadcast traffic coming from the pfsense box.  When observing it in wireshark (pic attached) it's tagged as vrrp, but from digging around in old posts I'm guessing it's actually carp?

    We have two firewall boxes which have been running without problems for several years (been on pfsense 1.2.2 for a while).  We have a lot of virtual ips setup as carp (with vhids from 1 through 46).  These virtual ip's are replicated to the backup firewall (along with rules, etc).  All failover and replication has been working without problems.

    Even though the broadcasts don't seem to be doing any damage, I'd really like to know if there's anything I can do to reduce the volume of them outbound on the WAN?

    If you need any more details let me know.


  • Rebel Alliance Developer Netgate

    No, that is normal traffic and required for CARP to function. Your ISP may be able to block the traffic on their side or at the CPE, but you need that traffic on the WAN (or WAN switch, rather) or CARP can't properly keep track of which hosts are alive and which should be master/backup.

    Even if you could reduce the overall frequency, it would take longer for a failure to be noticed, and thus longer for the failover to the backup unit to happen.



  • Ok, thanks.  That's what I figured.

    Out of curiosity, when I look at the wireshark logs the source is usually something like 'IETF-VRRP-virtual-router-VRID_14'.  I assume for this one the vhid was 14?  I ask because I see lots of others where the id appears to be hex (1b, 1d, 0c, etc) and wasn't sure about them?

    Thanks


  • Rebel Alliance Developer Netgate

    That may be the MAC address, which is algorithmically determined based off the VHID. If that is hex (which is likely) then that isn't 14, it's VHID 20 in decimal.



  • Quite possible.  I thought I'd seen some base 10 id's in wireshark as high as 45, but after glancing at it the highest non-hex is 29 which would make sense.

    Thanks for the help.



  • @jimp:

    No, that is normal traffic and required for CARP to function. Your ISP may be able to block the traffic on their side or at the CPE, but you need that traffic on the WAN (or WAN switch, rather) or CARP can't properly keep track of which hosts are alive and which should be master/backup.

    Is it possible to have CARP keep track of which hosts are alive and which should be master/backup via the LAN connection?



  • @Ree:

    Is it possible to have CARP keep track of which hosts are alive and which should be master/backup via the LAN connection?

    It's possible if you only want to run a CARP interface on your LAN. If you want the WAN to failover the WAN interfaces must exchange traffic.


  • Rebel Alliance Developer Netgate

    @Ree:

    Is it possible to have CARP keep track of which hosts are alive and which should be master/backup via the LAN connection?

    As dotdash said, that won't work.

    CARP puts a heartbeat on the wire where the interface containing the CARP IP is. The heartbeat is how it determines what is down. Each CARP member listens for heartbeats from other CARP hosts as well as sends its own heartbeat. If a CARP host sees no other heartbeats, it knows that something happened to the other box. Meanwhile, the other box might not even realize it has a problem.

    It's part of the fundamental architecture of CARP.



  • Thanks, that makes perfect sense.

    And I think I already know the answer to this next question, but just to be absolutely sure, is it that it's not a good idea to have the heartbeat sent out over just the LAN (or the OPT1 cross-over), or is it that it's just not possible?

    The reason I ask is because in our case we only really care about some sort of hardware failure taking down the master (in our setup if the WAN is down on our master, it's almost guaranteed to be down on our backup), so in theory just a simple "Master box is alive" heartbeat needs to be sent over the LAN or OPT1.

    But if the heartbeat absolutely has to be on the wire where the interface containing the CARP IP is, then I guess we'll just have to leave things as is.


  • Rebel Alliance Developer Netgate

    It absolutely has to be that way. It can't send a heartbeat for WAN over any other interface but WAN.

    In the case you describe, that could be solved by just putting a switch on the WAN side between your firewalls and the CPE. Even if your ISP link is down, the CARP traffic would still happen on the switch and they'd know that there wasn't a hardware failure.



  • Great, thanks again for the help.


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