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:lastproofread: 2021-06-30
.. _high-availability:
High availability
=================
VRRP (Virtual Router Redundancy Protocol) provides active/backup redundancy for
routers. Every VRRP router has a physical IP/IPv6 address, and a virtual
address. On startup, routers elect the master, and the router with the highest
priority becomes the master and assigns the virtual address to its interface.
All routers with lower priorities become backup routers. The master then starts
sending keepalive packets to notify other routers that it's available. If the
master fails and stops sending keepalive packets, the router with the next
highest priority becomes the new master and takes over the virtual address.
VRRP keepalive packets use multicast, and VRRP setups are limited to a single
datalink layer segment. You can setup multiple VRRP groups
(also called virtual routers). Virtual routers are identified by a
VRID (Virtual Router IDentifier). If you setup multiple groups on the same
interface, their VRIDs must be unique, but it's possible (even if not
recommended for readability reasons) to use duplicate VRIDs on different
interfaces.
Basic setup
-----------
VRRP groups are created with the
``set high-availability vrrp group $GROUP_NAME`` commands. The required
parameters are interface, vrid, and address.
minimal config
.. code-block:: none
set high-availability vrrp group Foo vrid 10
set high-availability vrrp group Foo interface eth0
set high-availability vrrp group Foo address 192.0.2.1/24
You can verify your VRRP group status with the operational mode
``run show vrrp`` command:
.. code-block:: none
vyos@vyos# run show vrrp
Name Interface VRID State Last Transition
---------- ----------- ------ ------- -----------------
Foo eth1 10 MASTER 2s
IPv6 support
------------
The ``address`` parameter can be either an IPv4 or IPv6 address, but you can
not mix IPv4 and IPv6 in the same group, and will need to create groups with
different VRIDs specially for IPv4 and IPv6.
Disabling a VRRP group
----------------------
You can disable a VRRP group with ``disable`` option:
.. code-block:: none
set high-availability vrrp group Foo disable
A disabled group will be removed from the VRRP process and your router will not
participate in VRRP for that VRID. It will disappear from operational mode
commands output, rather than enter the backup state.
Setting VRRP group priority
---------------------------
VRRP priority can be set with ``priority`` option:
.. code-block:: none
set high-availability vrrp group Foo priority 200
The priority must be an integer number from 1 to 255. Higher priority value
increases router's precedence in the master elections.
Sync groups
-----------
A sync group allows VRRP groups to transition together.
.. code-block:: none
edit high-availability vrrp
set sync-group MAIN member VLAN9
set sync-group MAIN member VLAN20
In the following example, when VLAN9 transitions, VLAN20 will also transition:
.. code-block:: none
vrrp {
group VLAN9 {
interface eth0.9
address 10.9.1.1/24
priority 200
vrid 9
}
group VLAN20 {
interface eth0.20
priority 200
address 10.20.20.1/24
vrid 20
}
sync-group MAIN {
member VLAN20
member VLAN9
}
}
.. warning:: All items in a sync group should be similarly configured.
If one VRRP group is set to a different preemption delay or priority,
it would result in an endless transition loop.
Preemption
----------
VRRP can use two modes: preemptive and non-preemptive. In the preemptive mode,
if a router with a higher priority fails and then comes back, routers with lower
priority will give up their master status. In non-preemptive mode, the newly
elected master will keep the master status and the virtual address indefinitely.
By default VRRP uses preemption. You can disable it with the "no-preempt"
option:
.. code-block:: none
set high-availability vrrp group Foo no-preempt
You can also configure the time interval for preemption with the "preempt-delay"
option. For example, to set the higher priority router to take over in 180
seconds, use:
.. code-block:: none
set high-availability vrrp group Foo preempt-delay 180
Unicast VRRP
------------
By default VRRP uses multicast packets. If your network does not support
multicast for whatever reason, you can make VRRP use unicast communication
instead.
.. code-block:: none
set high-availability vrrp group Foo peer-address 192.0.2.10
set high-availability vrrp group Foo hello-source-address 192.0.2.15
rfc3768-compatibility
---------------------
RFC 3768 defines a virtual MAC address to each VRRP virtual router.
This virtual router MAC address will be used as the source in all periodic VRRP
messages sent by the active node. When the rfc3768-compatibility option is set,
a new VRRP interface is created, to which the MAC address and the virtual IP
address is automatically assigned.
.. code-block:: none
set high-availability vrrp group Foo rfc3768-compatibility
Verification
.. code-block:: none
$show interfaces ethernet eth0v10
eth0v10@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
state UP group default qlen 1000
link/ether 00:00:5e:00:01:0a brd ff:ff:ff:ff:ff:ff
inet 172.25.0.247/16 scope global eth0v10
valid_lft forever preferred_lft forever
Scripting
---------
VRRP functionality can be extended with scripts. VyOS supports two kinds of
scripts: health check scripts and transition scripts. Health check scripts
execute custom checks in addition to the master router reachability. Transition
scripts are executed when VRRP state changes from master to backup or fault and
vice versa and can be used to enable or disable certain services, for example.
Health check scripts
^^^^^^^^^^^^^^^^^^^^
This setup will make the VRRP process execute the
``/config/scripts/vrrp-check.sh script`` every 60 seconds, and transition the
group to the fault state if it fails (i.e. exits with non-zero status) three
times:
.. code-block:: none
set high-availability vrrp group Foo health-check script /config/scripts/vrrp-check.sh
set high-availability vrrp group Foo health-check interval 60
set high-availability vrrp group Foo health-check failure-count 3
Transition scripts
^^^^^^^^^^^^^^^^^^
Transition scripts can help you implement various fixups, such as starting and
stopping services, or even modifying the VyOS config on VRRP transition.
This setup will make the VRRP process execute the
``/config/scripts/vrrp-fail.sh`` with argument ``Foo`` when VRRP fails,
and the ``/config/scripts/vrrp-master.sh`` when the router becomes the master:
.. code-block:: none
set high-availability vrrp group Foo transition-script backup "/config/scripts/vrrp-fail.sh Foo"
set high-availability vrrp group Foo transition-script fault "/config/scripts/vrrp-fail.sh Foo"
set high-availability vrrp group Foo transition-script master "/config/scripts/vrrp-master.sh Foo"
To know more about scripting, check the :ref:`command-scripting` section.
|
