IP Configuration: VRRP
Configurable Elements of VRRP
423 Cisco 500 Series Stackable Managed Switch Administration Guide
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All the VRRP routers supporting the same virtual router must have the same
configuration. If the configurations are different, the configuration of the master is
used. A backup VRRP router syslogs a message when its configuration is different
from the configuration of the master.
Source IP Address In a VRRP Router
Each VRRP router supporting a virtual router uses their own IP address as the
source IP address in their outgoing VRRP messages for the virtual router. VRRP
routers of the same virtual router communicate to each other in VRRP messages. If
a VRRP router is the owner of the IP address of the virtual router, then IP address is
one of the virtual router IP addresses. If a VRRP router is not the owner of the IP
address of the virtual router, then the IP address is the IP address of the VRRP
router interface to the same IP subnet of the virtual router.
If the source IP address was manually configured, the configuration is removed
and the default source IP address is taken (lowest VRRP router's IP address
defined on the interface). If the source IP address was a default one, a new default
source IP address is taken.
VRRP Router Priority and Preemption
An important aspect of the VRRP redundancy scheme is the ability to assign each
VRRP router a VRRP priority. The VRRP priority must express how efficiently a
VRRP router would perform as a backup to a virtual router defined in the VRRP
router. If there are multiple backup VRRP routers for the virtual router, the priority
determines which backup VRRP router is assigned as master if the current master
fails.
If a virtual router is the owner of the IP address, its VRRP priority is automatically
assigned with priority of 255 by the system, and the VRRP router (on which this
virtual router is assigned) automatically functions as a virtual router master if it is
up.
In Figure , if Router A, the virtual router master, fails, a selection process takes
place to determine if virtual router backups B or C must take over. If Routers B and
C are configured with the priorities of 101 and 100, respectively, Router B is
elected to become virtual router master because it has the higher priority. If both
have the same priority, the one with the higher IP address value is selected to
become the virtual router master.
By default, a preemptive feature is enabled, which functions as follows:
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