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from the slave (for example, when master is failing on disk IO and could not be logged into or execute cronjob). Commented out examples changed too to simplify future merging. Idea by: kaa@zvuki.ru Discussed with: glebius MFC after: 1 week
324 lines
11 KiB
Groff
324 lines
11 KiB
Groff
.\" $OpenBSD: carp.4,v 1.16 2004/12/07 23:41:35 jmc Exp $
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.\"
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.\" Copyright (c) 2003, Ryan McBride. All rights reserved.
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.\" Copyright (c) 2011, Gleb Smirnoff <glebius@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 21, 2013
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.Dt CARP 4
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.Os
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.Sh NAME
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.Nm carp
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.Nd Common Address Redundancy Protocol
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.Sh SYNOPSIS
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.Cd "device carp"
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.Sh DESCRIPTION
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The CARP allows multiple hosts on the same local network to share a set of
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IPv4 and/or IPv6 addresses.
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Its primary purpose is to ensure that these
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addresses are always available.
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.Pp
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To use
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.Nm ,
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the administrator needs to configure at a minimum a common virtual host ID
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(vhid), and attach at least one IP address to this vhid on each machine which
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is to take part in the virtual group.
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Additional parameters can also be set on a per-vhid basis:
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.Cm advbase
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and
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.Cm advskew ,
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which are used to control how frequently the host sends advertisements when it
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is the master for a virtual host, and
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.Cm pass
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which is used to authenticate
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.Nm
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advertisements.
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The
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.Cm advbase
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parameter stands for
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.Dq "advertisement base" .
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It is measured in seconds and specifies the base of the advertisement interval.
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The
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.Cm advskew
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parameter stands for
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.Dq "advertisement skew" .
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It is measured in 1/256 of seconds.
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It is added to the base advertisement interval to make one host advertise
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a bit slower that the other does.
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Both
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.Cm advbase
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and
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.Cm advskew
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are put inside CARP advertisements.
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These values can be configured using
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.Xr ifconfig 8 ,
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or through the
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.Dv SIOCSVH
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.Xr ioctl 2 .
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.Pp
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CARP virtual hosts can be configured on multicast-capable interfaces: Ethernet,
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layer 2 VLAN, FDDI and Token Ring.
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An arbitrary number of virtual host IDs can be configured on an interface.
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An arbitrary number of IPv4 or IPv6 addresses can be attached to a particular
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vhid.
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It is important that all hosts participating in a vhid have the same list
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of prefixes configured on the vhid, since all prefixes are included in the
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cryptographic checksum supplied in each advertisement.
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Multiple vhids running on one interface participate in master/backup
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elections independently.
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.Pp
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Additionally, there are a number of global parameters which can be set using
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.Xr sysctl 8 :
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.Bl -tag -width ".Va net.inet.carp.ifdown_demotion_factor"
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.It Va net.inet.carp.allow
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Accept incoming
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.Nm
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packets.
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Enabled by default.
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.It Va net.inet.carp.preempt
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Allow virtual hosts to preempt each other.
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When enabled, a vhid in a backup state would preempt a master that
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is announcing itself with a lower advskew.
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Disabled by default.
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.It Va net.inet.carp.log
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Determines what events relating to
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.Nm
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vhids are logged.
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A value of 0 disables any logging.
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A value of 1 enables logging state changes of
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.Nm
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vhids.
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Values above 1 enable logging of bad
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.Nm
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packets.
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The default value is 1.
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.It Va net.inet.carp.demotion
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This value shows current level of CARP demotion.
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The value is added to the actual advskew sent in announcements for
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all vhids.
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At normal system operation the demotion factor is zero.
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However, problematic conditions raise its level: when
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.Nm
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experiences problem with sending announcements, when an interface
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running a vhid goes down, or while the
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.Xr pfsync 4
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interface is not synchronized.
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The demotion factor can be adjusted writing to the sysctl oid.
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The signed value supplied to the
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.Xr sysctl 8
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command is added to current demotion factor.
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This allows to control
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.Nm
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behaviour depending on some external conditions, for example on the status
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of some daemon utility.
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.It Va net.inet.carp.ifdown_demotion_factor
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This value is added to
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.Va net.inet.carp.demotion
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when an interface running a vhid goes down.
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The default value is 240 (the maximum advskew value).
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.It Va net.inet.carp.senderr_demotion_factor
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This value is added to
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.Va net.inet.carp.demotion
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when
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.Nm
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experiences errors sending its announcements.
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The default value is 240 (the maximum advskew value).
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.El
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.\".Sh ARP level load balancing
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.\"A
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.\".Nm
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.\"interface has limited abilities for load balancing incoming connections
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.\"between hosts in an Ethernet network.
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.\"For load-balancing operation, one needs several CARP interfaces that
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.\"are configured to the same IP address, but to a different vhids.
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.\"Once an ARP request is received, the CARP protocol will use a hashing
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.\"function against the source IP address in the ARP request to determine
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.\"which vhid the request will be assigned to.
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.\"If the corresponding CARP interface is the current
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.\"master interface, a reply will
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.\"be sent to the ARP request;
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.\"otherwise it will be ignored.
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.\"See the
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.\".Sx EXAMPLES
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.\"section for a practical example of load balancing.
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.\".Pp
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.\"The ARP load balancing implemented in
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.\".Nm
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.\"has some limitations.
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.\"First, ARP balancing only works on the local network segment.
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.\"It cannot balance traffic that crosses a router, because the
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.\"router itself will always be balanced to the same virtual host.
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.\"Second, ARP load balancing can lead to asymmetric routing
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.\"of incoming and outgoing traffic, and thus combining it with
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.\".Xr pfsync 4
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.\"is dangerous, because this creates a race condition between
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.\"balanced routers and a host they are serving.
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.\"Imagine an incoming packet creating state on the first router, being
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.\"forwarded to its destination, and the destination replying faster
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.\"than the state information is packed and synced with the second router.
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.\"If the reply would be load balanced to second router, it will be
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.\"dropped since the second router has not yet received information about
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.\"the connection state.
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.Sh STATE CHANGE NOTIFICATIONS
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Sometimes it is useful to get notified about
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.Nm
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status change events.
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This can be accomplished by using
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.Xr devd 8
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hooks.
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Master/slave events are signalled under system
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.Dv CARP .
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The subsystem specifies the vhid and name of the interface where
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the master/slave event occurred.
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The type of the message displays the new state of the vhid.
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Please see
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.Xr devd.conf 5
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and the
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.Sx EXAMPLES
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section for more information.
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.Sh EXAMPLES
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For firewalls and routers with multiple interfaces, it is desirable to
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failover all of the addresses running
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.Nm
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together, when one of the physical interfaces goes down.
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This is achieved by the use of the preempt option.
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Enable it on both hosts A and B:
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.Pp
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.Dl sysctl net.inet.carp.preempt=1
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.Pp
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Assume that host A is the preferred master and we are running the
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192.168.1.0/24 prefix on em0 and 192.168.2.0/24 on em1.
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This is the setup for host A (advskew is above 0 so it could be overwritten
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in the emergency situation from the other host):
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.Bd -literal -offset indent
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ifconfig em0 vhid 1 advskew 100 pass mekmitasdigoat 192.168.1.1/24
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ifconfig em1 vhid 2 advskew 100 pass mekmitasdigoat 192.168.2.1/24
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.Ed
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.Pp
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The setup for host B is identical, but it has a higher
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.Cm advskew :
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.Bd -literal -offset indent
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ifconfig em0 vhid 1 advskew 200 pass mekmitasdigoat 192.168.1.1/24
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ifconfig em1 vhid 2 advskew 200 pass mekmitasdigoat 192.168.2.1/24
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.Ed
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.Pp
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When one of the physical interfaces of host A fails,
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.Cm advskew
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is demoted to a configured value on all its
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.Nm
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vhids.
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Due to the preempt option, host B would start announcing itself, and thus
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preempt host A on both interfaces instead of just the failed one.
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.\".Pp
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.\"In order to set up an ARP balanced virtual host, it is necessary to configure
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.\"one virtual host for each physical host which would respond to ARP requests
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.\"and thus handle the traffic.
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.\"In the following example, two virtual hosts are configured on two hosts to
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.\"provide balancing and failover for the IP address 192.168.1.10.
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.\".Pp
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.\"First the
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.\".Nm
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.\"interfaces on host A are configured.
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.\"The
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.\".Cm advskew
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.\"of 100 on the second virtual host means that its advertisements will be sent
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.\"out slightly less frequently.
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.\".Bd -literal -offset indent
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.\"ifconfig carp0 create
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.\"ifconfig carp0 vhid 1 advskew 100 pass mekmitasdigoat 192.168.1.10/24
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.\"ifconfig carp1 create
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.\"ifconfig carp1 vhid 2 advskew 200 pass mekmitasdigoat 192.168.1.10/24
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.\".Ed
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.\".Pp
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.\"The configuration for host B is identical, except the
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.\".Cm advskew
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.\"is on virtual host 1 rather than virtual host 2.
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.\".Bd -literal -offset indent
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.\"ifconfig carp0 create
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.\"ifconfig carp0 vhid 1 advskew 200 pass mekmitasdigoat 192.168.1.10/24
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.\"ifconfig carp1 create
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.\"ifconfig carp1 vhid 2 advskew 100 pass mekmitasdigoat 192.168.1.10/24
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.\".Ed
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.\".Pp
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.\"Finally, the ARP balancing feature must be enabled on both hosts:
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.\".Pp
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.\".Dl sysctl net.inet.carp.arpbalance=1
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.\".Pp
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.\"When the hosts receive an ARP request for 192.168.1.10, the source IP address
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.\"of the request is used to compute which virtual host should answer the request.
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.\"The host which is master of the selected virtual host will reply to the
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.\"request, the other(s) will ignore it.
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.\".Pp
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.\"This way, locally connected systems will receive different ARP replies and
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.\"subsequent IP traffic will be balanced among the hosts.
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.\"If one of the hosts fails, the other will take over the virtual MAC address,
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.\"and begin answering ARP requests on its behalf.
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.Pp
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Processing of
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.Nm
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status change events can be set up by using the following devd.conf rule:
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.Bd -literal -offset indent
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notify 0 {
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match "system" "CARP";
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match "subsystem" "[0-9]+@[0-9a-z]+";
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match "type" "(MASTER|BACKUP)";
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action "/root/carpcontrol.sh $subsystem $type";
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};
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.Ed
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.Pp
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To see
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.Nm
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packets decoded in
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.Xr tcpdump 8
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output, one needs to specify
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.Fl T Ar carp
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option, otherwise
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.Xr tcpdump 8
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tries to interpret them as VRRP packets:
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.Bd -literal -offset indent
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tcpdump -npi vlan0 -T carp
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.Ed
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.Sh SEE ALSO
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.Xr inet 4 ,
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.Xr pfsync 4 ,
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.Xr rc.conf 5 ,
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.Xr devd.conf 5 ,
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.Xr ifconfig 8 ,
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.Xr sysctl 8
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.Xr tcpdump 8
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.Sh HISTORY
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The
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.Nm
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device first appeared in
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.Ox 3.5 .
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The
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.Nm
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device was imported into
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.Fx 5.4 .
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In
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.Fx 10.0 ,
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.Nm
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was significantly rewritten, and is no longer a pseudo-interface.
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