svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
carp(4)
CARP(4) BSD Kernel Interfaces Manual CARP(4)
NAME
carp — Common Address Redundancy Protocol
SYNOPSIS
device carp
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.
To use carp, 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: advbase and advskew,
which are used to control how frequently the host sends advertisements
when it is the master for a virtual host, and pass which is used to
authenticate carp advertisements. The advbase parameter stands for
“advertisement base”. It is measured in seconds and specifies the base
of the advertisement interval. The advskew parameter stands for
“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 advbase and advskew are put inside CARP
advertisements. These values can be configured using ifconfig(8), or
through the SIOCSVH ioctl(2).
CARP virtual hosts can be configured on multicast-capable interfaces:
Ethernet, layer 2 VLAN, FDDI and Token Ring. An arbitrary number of vir‐
tual 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 the prefixes are included in
the cryptographic checksum supplied in each advertisement. Multiple
vhids running on one interface participate in master/backup elections
independently.
Additionally, there are a number of global parameters which can be set
using sysctl(8):
net.inet.carp.allow Allow carp operation. When dis‐
abled, virtual hosts remain in ini‐
tial state, neither sending nor
receiving announcements or traffic.
Enabled by default.
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.
net.inet.carp.dscp DSCP value in carp packet. Valid
Values are 0 to 63. A value of 4
is equivalent to the old standard
of TOS LOW_DELAY. TOS values were
deprecated and replaced by DSCP in
1998. The default value is 56
(CS7/Network Control).
net.inet.carp.log Determines what events relating to
carp vhids are logged. A value of
0 disables any logging. A value of
1 enables logging state changes of
carp vhids. Values above 1 enable
logging of bad carp packets. The
default value is 1.
net.inet.carp.demotion This value shows the current level
of CARP demotion. The value is
added to the actual advskew sent in
announcements for all vhids. Dur‐
ing normal system operation the
demotion factor is zero. However,
problematic conditions raise its
level: when carp experiences prob‐
lem with sending announcements,
when an interface running a vhid
goes down, or while the pfsync(4)
interface is not synchronized. The
demotion factor can be adjusted
writing to the sysctl oid. The
signed value supplied to the
sysctl(8) command is added to cur‐
rent demotion factor. This allows
to control carp behaviour depending
on some external conditions, for
example on the status of some dae‐
mon utility.
net.inet.carp.ifdown_demotion_factor This value is added to
net.inet.carp.demotion when an
interface running a vhid goes down.
The default value is 240 (the maxi‐
mum advskew value).
net.inet.carp.senderr_demotion_factor
This value is added to
net.inet.carp.demotion when carp
experiences errors sending its
announcements. The default value
is 240 (the maximum advskew value).
STATE CHANGE NOTIFICATIONS
Sometimes it is useful to get notified about carp status change events.
This can be accomplished by using devd(8) hooks. Master/slave events are
signalled under system 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 devd.conf(5) and
the EXAMPLES section for more information.
EXAMPLES
For firewalls and routers with multiple interfaces, it is desirable to
failover all of the addresses running carp together, when one of the
physical interfaces goes down. This is achieved by the use of the pre‐
empt option. Enable it on both hosts A and B:
sysctl net.inet.carp.preempt=1
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 set‐
up for host A (advskew is above 0 so it could be overwritten in the emer‐
gency situation from the other host):
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
The setup for host B is identical, but it has a higher advskew:
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
When one of the physical interfaces of host A fails, advskew is demoted
to a configured value on all its carp 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.
Processing of carp status change events can be set up by using the fol‐
lowing devd.conf rule:
notify 0 {
match "system" "CARP";
match "subsystem" "[0-9]+@[0-9a-z]+";
match "type" "(MASTER|BACKUP)";
action "/root/carpcontrol.sh $subsystem $type";
};
To see carp packets decoded in tcpdump(1) output, one needs to specify
the -T carp option, otherwise tcpdump(1) will interpret them as VRRP
packets:
tcpdump -npi vlan0 -T carp
SEE ALSO
tcpdump(1), inet(4), pfsync(4), devd.conf(5), rc.conf(5), ifconfig(8),
sysctl(8)
HISTORY
The carp device first appeared in OpenBSD 3.5. The carp device was
imported into FreeBSD 5.4. In FreeBSD 10.0, carp was significantly
rewritten, and is no longer a pseudo-interface.
BSD July 1, 2018 BSD