3Com 4007, Руководство по внедрению, Страница: 401 / 684

Key Concepts 401
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Virtual router master — The VRRP router that forwards packets sent
to the IP addresses associated with the virtual router. Also called the
Master router. A virtual router is the Master when:
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You configure it (using the Administration console, the Web
Management console, or SNMP) as the primary IP address for a
given interface.
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Backing up a Master that has been disconnected or disabled.
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Virtual router backup — The VRRP router that assumes packet
forwarding responsibility for a virtual router if the Master fails. Also
called the Backup router.
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IP address owner — The router that is the original owner of the IP
addresses that virtual router incorporates into its own IP address set.
The IP address owner must be a VRRP participant.
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Primary IP address — An IP address selected from the set of available
interface addresses. This is the IP address that VRRP uses in its
advertisements that supply the source of the IP packet.
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Virtual router initialize — A state in which a virtual router is defined
but not enabled. A virtual router is also in the initialize state when its
associated interface is not operational.
How VRRP Works When you assign Master router responsibilities to one of the virtual
routers on the LAN, the Master controls the IP addresses associated with
a virtual router. The Master router forwards the IP packets sent to the IP
addresses it controls.
The backup process works as follows. The Master router sends out
periodic VRRP advertisement messages, at time intervals you set, to the
other VRRP routers and to the hosts on the common LAN. (A VRRP
advertisement consists of the IP addresses that the Master owns and the
virtual MAC address of the virtual router.) If the Master stops forwarding
advertisements to the other routers for a predetermined period of time,
the other routers automatically enter an election process to determine
which router takes over Master responsibilities.
After the original Master again become operational, it begins again to
broadcast advertisements to the other virtual routers if pre-empt mode is
enabled. Packet forwarding responsibility then shifts back to the original
Master router.