Avaya P580 User Manual page 401

Assigning
Priorities to Virtual
Routers
Selecting an
Advertisement
Interval
Deciding to Use
Authentication
Changing the
Primary IP
address
Document No. 650-100-700, Issue 1
This is especially helpful in a network where a routing protocol is
used (RIP, OSPF). In most cases, the VRRP election process will
take place before the routing table has been updated. This may cause
a longer period of traffic loss.
The allowed configurable range for the Priority of a virtual router is 1-254.
255 is reserved for a virtual router that is IP Address Owner (as described
above). If two routers are participating in VRRP, making the desired Master
router 254 (or 255 if IP Address Owner) and the Backup router 100 (the
default Priority) is a common configuration. If multiple routers will be
backing up the Master router, then the Priorities can be assigned in
descending order (100, 99, 98, etc., for example).
Equal Priorities are also allowed but may be more difficult to troubleshoot.
If two Master routers have the same Priority (and the same VRRP settings),
the VRRP election process then checks the associated IP Address of each
virtual router. In that case, the associated IP Address with a higher value
becomes Master. However, if a Master and Backup virtual router have the
same Priority, the Backup will not become Master even if it has a higher
associated IP Address. In other words, equal priorities are not enough for a
backup router that is already in the Primary state to become Backup.
In most cases, leaving the Advertisement Interval to its default value of 1 is
adequate. Usually, this is also desired because it will allow for the fastest
fail over time. As described above, the time a Backup will become Master if
it stops receiving advertisements is approximately three times this value in
seconds. A higher value may be selected if the network is very stable and
less advertisement traffic is desired. In any case, it is not recommended that
the interval be increased to values above five or six.
In networks where there is little or no security risk and a minimal chance of
miscommunication, authentication is probably not needed. Using Simple
Text Password authentication can provide protection against accidental
misconfiguration. The correct password must be entered for a new virtual
router before it will begin the VRRP election process with another virtual
router. Simple Text Password authentication does not provide protection
from hostile attacks.
If there is a virtual router that is an IP Address Owner created on an IP
interface, the priority will be changed to 100 (default) if the Primary IP
Address is changed, because a Priority of 255 is reserved for the IP Address
Owner only.
If the virtual router is a non-Address Owner and the associated Primary IP
Address is changed to the same as the virtual router IP Address, the Priority
of that virtual router is changed to 255, since it is now the IP Address
Owner.
Configuring IP Routing
12-85