The path for a virtual link is through an area shared by the neighbor ABR (router with a physical backbone connection) and the ABR
requiring a logical connection to the backbone.
Two parameters must be dened for all virtual links -- transit area ID and neighbor router:
• The transit area ID represents the shared area of the two ABRs and serves as the connection point between the two routers. This
number should match the area ID value.
• The neighbor router is the router ID (IPv4 address) of the router that is physically connected to the backbone when assigned
from the router interface requiring a logical connection. The neighbor router is the router ID (IPv4 address) of the router requiring
a logical connection to the backbone when assigned from the router interface with the physical connection.
NOTE
By default, the router ID is the IPv4 address congured on the lowest-numbered loopback interface. If the device does not have
a loopback interface, the default router ID is the lowest-numbered IPv4 address congured on the device.
When you establish an area virtual link, you must congure it on both ends of the virtual link. For example, imagine that ABR1 in areas 1
and 2 is cut o from the backbone area (area 0). To provide backbone access to ABR1, you can add a virtual link between ABR1 and
ABR2 in area 1 using area 1 as a transit area. To congure the virtual link, you dene the link on the router that is at each end of the link.
No conguration for the virtual link is required on the routers in the transit area.
To dene the virtual link on ABR1, enter the following command on ABR1.
device(config-ospf6-router)# area 1 virtual-link 10.157.22.1
To dene the virtual link on ABR2, enter the following command on ABR2.
device(config-ospf6-router)# area 1 virtual-link 10.0.0.1
Syntax: [no] area {number | ipv4-address} virtual-link router-id
The number and ipv4-address parameters specify the transit area ID, area number, which can be a number, or in IPv4 address format. If
you specify a number, the number can be from 0 through 2,147,483,647.
The router-id parameter species the router ID of the OSPF router at the remote end of the virtual link. To display the router ID on a
router, enter the show ip command.
Modifying virtual link parameters
You can modify the following virtual link parameters:
• Dead-interval: The number of seconds that a neighbor router waits for a hello packet from the device before declaring the router
is down. The range is from 1 through 65535 seconds. The default is 40 seconds.
• Hello-interval: The length of time between the transmission of hello packets. The range is from 1 through 65535 seconds. The
default is 10 seconds.
• Retransmit-interval: The interval between the retransmission of link state advertisements to router adjacencies for this interface.
The range is from 0 through 3600 seconds. The default is 5 seconds.
• Transmit-delay: The period of time it takes to transmit Link State Update packets on the interface. The range is from 0 through
3600 seconds. The default is 1 second.
NOTE
The values of the dead-interval and hello-interval parameters must be the same at both ends of a virtual link. Therefore, if you
modify the values of these parameters at one end of a virtual link, you must make the same modications on the other end of
the link.The values of the other virtual link parameters do not require synchronization.
Conguring OSPFv3
FastIron Ethernet Switch Layer 3 Routing
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