3Com CoreBuilder 3500, Руководство по внедрению

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322 C
HAPTER
12: V
IRTUAL
R
OUTER
R
EDUNDANCY
P
ROTOCOL
(VRRP)
Important
Considerations
This section provides information to be aware of when you implement
VRRP:
■
The Master router forwards the IP addresses that you have associated
with the primary virtual router, and:
■
Responds to ARP requests for the IP address or addresses that are
associated with the virtual router.
■
Forwards packets that have a destination Link Layer MAC address
that matches the virtual router MAC address. In other words, the
Master forwards packets that hosts have sent to the virtual router
to be routed.
■
Discards packets addressed to the IP address or addresses
associated with the virtual router if the virtual router is not the IP
address owner. Otherwise, ping, SNMP, and Telnet do not function
properly.
■
Sends periodic VRRP advertisement messages. (Set the advertising
interval to be short enough to provide a timely transition to
another router should the Master fail. Try an advertising interval of
1 second.)
■
A Backup router monitors the availability and state of the Master, and:
■
Does not respond to ARP requests for the IP address or addresses
associated with the virtual router.
■
Discards packets that have a destination Link Layer MAC address
that matches the virtual router MAC address.
■
Does not accept packets addressed to the IP address or addresses
associated with the virtual router
■
Hosts obtain the virtual router’s MAC address by means of an ARP
broadcast.
■
VRRP is not a routing protocol, and it is only as useful as the design of
the network upon which it is implemented. Good network design is
critical in ensuring the success of router redundancy.
■
The virtual routers must be on the same VLAN.