3Com CoreBuilder 3500, Руководство по внедрению, Страница: 380 / 592

380 C
HAPTER
14: O
PEN
S
HORTEST
P
ATH
F
IRST
(OSPF)
OSPF Interfaces
You configure OSPF router interfaces by adding OSPF characteristics to
existing IP VLAN interfaces. The OSPF interface has the following
characteristics and statistics, which are discussed in the next sections:
■
Mode
■
Priority
■
Area ID
■
Cost
■
Delay
■
Hello Interval
■
Retransmit Interval
■
Dead Interval
■
Password
■
Statistics
Mode The mode for an interface can be
off
or
active
. To run OSPF routing on
the interface, set the mode to active .
Priority You assign the interface priority to an OSPF router to determine its status
as a designated router. A router can function in one of three ways:
■
Designated router (DR) — The router that has the highest priority
value, unless a designated router already exists on the network
segment.
■
Backup designated router (BDR) — The router that has a lower
priority than the DR; the BDR takes over DR functions if the DR fails.
■
Not a designated router — Any router that is given a priority of 0 or
that is not elected DR or BDR. Priority 0 routers can never be elected as
a DR or a BDR.
Using Priority to Select a Designated Router
Each OSPF area on a broadcast or nonbroadcast multiaccess network that
has at least two attached routers requires a designated router and a
backup designated router. The designated router (DR) forms adjacencies
to all other routers in the area. If for any reason the DR fails, the backup
designated router takes over as the designated router.