Date: Wed, 8 Jun 2016 11:19:44 -0500 From: Matthew Grooms <mgrooms@shrew.net> To: freebsd-net@freebsd.org Subject: Re: Getting CARP to broadcast on a different interface Message-ID: <c323f35c-e043-a391-2aba-de67e7134047@shrew.net> In-Reply-To: <SN1PR08MB1821CE60861ADDD84BA20CEEBA5E0@SN1PR08MB1821.namprd08.prod.outlook.com> References: <20160608124310.GG2050@box-hlm-03.niklaas.eu> <SN1PR08MB1821CE60861ADDD84BA20CEEBA5E0@SN1PR08MB1821.namprd08.prod.outlook.com>
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On 6/8/2016 10:15 AM, David DeSimone wrote: > One of the purposes of the CARP announcements is to announce the > location of the virtual mac address to the upstream switch fabric. > Since CARP uses a virtual mac that floats between multiple ports, you > need to have the CARP master continually assert that its particular > port is the target that should be used for delivery of packets to the > virtual MAC address. Without this function, switches might still > mistakenly deliver their frames to the standby node. > > The CARP announcements are also helpful in detecting and routing > around some odd failure scenarios, such as a failure within the > upstream fabric, where the master sees link on its port, but can't > actually send frames that reach the rest of the network. If the > standby can't hear the master's announcements any more, it can > promote itself to master and hopefully keep your cluster online. > This would not happen without the announcement feature. > > I would hope you could explain this to your provider and get them to > white-list CARP announcements because they are defeating important > safety features you wish to use. > You just need a gratuitous ARP on the new switch port after the MAC is migrated. That's how VMs move quickly between hypervisors with almost no downtime. As soon as a MAC is seen on a new port, the switch should overwrite it's notion of the port to MAC association. https://wiki.wireshark.org/Gratuitous_ARP As for the standby node, it should never announce unless the master node fails to suppress it. -Matthew
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