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Command Mode: OSPF protocol configuration mode
Usage Guide: An area can be configured to a STUB area if the area has only one egress
point (connect to one layer3 switch only), or need not select egress point for each exterior
destination. Type4 LSA (ASBR summary LSA) and type5 LSA (AS exterior LSA) are not
allowed to flood into/through STUB areas, this saves the resource for processing exterior
routing information for layer3 switches inside the area.
Example: Set area 1 to be a STUB area with a default routing cost of 60.
Switch(Config-Router-Ospf)#stub cost 60 area 1
15.4.2.2.21 virtuallink neighborid
Command: virtuallink neighborid <router_id> transitarea <area_id> [hellointerval
<time>] [deadinterval <time>] [retransmit<time>] [transitdelay <time>]
no virtuallink neighborid <router_id> transitarea <area_id>
Function: Create and configure virtual link; the “no virtuallink neighborid <router_id>
transitarea <area_id>” command deletes a virtual link.
Parameter: is the ID for the virtual link neighbor in dotted decimal format; is the area
number for transit area, ranging from 0 to 42,949,67,295; the rest four parameters are
optional intervals that has the same meaning as those in OSPF interface mode.
Default: No virtual link is configured by default.
Command Mode: OSPF protocol configuration mode
Usage Guide: The introduction of virtual link is to fulfill or enhance the connectivity of the
backbone area (area 0). As the backbone area must keep connected logically, if no
in-area route exists between two nodes within the backbone area, a virtual link must be
established between the two nodes across a transit area. Virtual link is identified by the ID
of the partner layer3 switch. The non-backbone area providing interior route for both ends
of the virtual link is referred to a “transit area”, the area number must be specified on
configuration.
A virtual link is activated when the route across the transit area is calculated, and
practically forms a point-to-point connection between the two ends. In this connection,
interface parameters (such as HELLO interval) can be configured just as on a physical
interface.
Example: Configure a virtual link to 11.1.1.1 via transit area 2.
Switch(Config-Router-Ospf)#virtuallink neighborid 11.1.1.1 transitarea 2
15.4.2.2.22 show ip ospf
Command: show ip ospf
Function: Display major OSPF information.
Default: Not displayed.