267 lines
8.5 KiB
Groff
267 lines
8.5 KiB
Groff
.\" $OpenBSD: carp.4,v 1.16 2004/12/07 23:41:35 jmc Exp $
|
|
.\"
|
|
.\" Copyright (c) 2003, Ryan McBride. All rights reserved.
|
|
.\"
|
|
.\" 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 January 5, 2010
|
|
.Dt CARP 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm carp
|
|
.Nd Common Address Redundancy Protocol
|
|
.Sh SYNOPSIS
|
|
.Cd "device carp"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
interface is a pseudo-device that implements and controls the
|
|
CARP protocol.
|
|
CARP allows multiple hosts on the same local network to share a set of IP addresses.
|
|
Its primary purpose is to ensure that these
|
|
addresses are always available, but in some configurations
|
|
.Nm
|
|
can also provide load balancing functionality.
|
|
.Pp
|
|
A
|
|
.Nm
|
|
interface can be created at runtime using the
|
|
.Nm ifconfig Li carp Ns Ar N Cm create
|
|
command or by configuring
|
|
it via
|
|
.Va cloned_interfaces
|
|
in the
|
|
.Pa /etc/rc.conf
|
|
file.
|
|
.Pp
|
|
To use
|
|
.Nm ,
|
|
the administrator needs to configure at minimum a common virtual host ID (VHID)
|
|
and virtual host IP address on each machine which is to take part in the virtual
|
|
group.
|
|
Additional parameters can also be set on a per-interface 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 configurations can be done using
|
|
.Xr ifconfig 8 ,
|
|
or through the
|
|
.Dv SIOCSVH
|
|
.Xr ioctl 2 .
|
|
.Pp
|
|
Additionally, there are a number of global parameters which can be set using
|
|
.Xr sysctl 8 :
|
|
.Bl -tag -width ".Va net.inet.carp.arpbalance"
|
|
.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.
|
|
It is also used to failover
|
|
.Nm
|
|
interfaces as a group.
|
|
When the option is enabled and one of the
|
|
.Nm
|
|
enabled physical interfaces
|
|
goes down,
|
|
.Cm advskew
|
|
is changed to 240 on all
|
|
.Nm
|
|
interfaces.
|
|
See also the first example.
|
|
Disabled by default.
|
|
.It Va net.inet.carp.log
|
|
Value of 0 disables any logging.
|
|
Value of 1 enables logging state changes of
|
|
.Nm
|
|
interfaces.
|
|
Values above 1 enable logging of bad
|
|
.Nm
|
|
packets.
|
|
Default value is 1.
|
|
.It Va net.inet.carp.arpbalance
|
|
Balance local traffic using ARP (see below).
|
|
Disabled by default.
|
|
.It Va net.inet.carp.suppress_preempt
|
|
A read only value showing the status of preemption suppression.
|
|
Preemption can be suppressed if link on an interface is down
|
|
or when
|
|
.Xr pfsync 4
|
|
interface is not synchronized.
|
|
Value of 0 means that preemption is not suppressed, since no
|
|
problems are detected.
|
|
Every problem increments suppression counter.
|
|
.El
|
|
.Sh ARP level load balancing
|
|
The
|
|
.Nm
|
|
has limited abilities for load balancing the incoming connections
|
|
between hosts in 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 should this request belong to.
|
|
If the corresponding CARP interface is in master state, the ARP request
|
|
will be replied, otherwise it will be ignored.
|
|
See the
|
|
.Sx EXAMPLES
|
|
section for a practical example of load balancing.
|
|
.Pp
|
|
The ARP load balancing 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 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 due to no state.
|
|
.Sh EXAMPLES
|
|
For firewalls and routers with multiple interfaces, it is desirable to
|
|
failover all of the
|
|
.Nm
|
|
interfaces together, when one of the physical interfaces goes down.
|
|
This is achieved by the preempt option.
|
|
Enable it on both host A and B:
|
|
.Pp
|
|
.Dl sysctl net.inet.carp.preempt=1
|
|
.Pp
|
|
Assume that host A is the preferred master and 192.168.1.x/24 is
|
|
configured on one physical interface and 192.168.2.y/24 on another.
|
|
This is the setup for host A:
|
|
.Bd -literal -offset indent
|
|
ifconfig carp0 create
|
|
ifconfig carp0 vhid 1 pass mekmitasdigoat 192.168.1.1/24
|
|
ifconfig carp1 create
|
|
ifconfig carp1 vhid 2 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 carp0 create
|
|
ifconfig carp0 vhid 1 advskew 100 pass mekmitasdigoat 192.168.1.1/24
|
|
ifconfig carp1 create
|
|
ifconfig carp1 vhid 2 advskew 100 pass mekmitasdigoat 192.168.2.1/24
|
|
.Ed
|
|
.Pp
|
|
Because of the preempt option, when one of the physical interfaces of
|
|
host A fails,
|
|
.Cm advskew
|
|
is adjusted to 240 on all its
|
|
.Nm
|
|
interfaces.
|
|
This will cause host B to preempt 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 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
|
|
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 100 pass mekmitasdigoat 192.168.1.10/24
|
|
ifconfig carp1 create
|
|
ifconfig carp1 vhid 2 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.
|
|
.Sh SEE ALSO
|
|
.Xr inet 4 ,
|
|
.Xr pfsync 4 ,
|
|
.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 .
|