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