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What is the use of virtual link in OSPF?
What Are Virtual Links? All areas in an OSPF autonomous system must be physically connected to the backbone area (area 0). In some cases where this physical connection is not possible, you can use a virtual link to connect to the backbone through a non-backbone area.
What are virtual links?
A virtual link is not a physical link. It is a logical link using the least cost path between the ABR of the non-backbone connected area and the backbone ABR of the transit area. A virtual adjacency across the virtual link is formed, and routing information is exchanged.
What is the purpose of virtual link?
To provide backbone access to Device A, you can add a virtual link between Device A and Device C using Area 1 as a transit area. To configure the virtual link, you define the link on the router that is at each end of the link. No configuration for the virtual link is required on the routers in the transit area.
What are OSPF areas and virtual links?
By definition an OSPF area is a collection of networks, not a collection of routers. A backbone network segment is an IP subnet that belongs to the area identified by 0.0. 0.0. Areas that are not physically connected to the backbone are logically connected by a backbone ABR using an OSPF virtual link.
How do I create a virtual link?
Use the area virtual-link command to establish a virtual link from a remote area to the backbone area. In OSPF, all areas must be connected to a backbone area. If the connection to the backbone is lost, it can be repaired by establishing a virtual link.
How do I set up a virtual link?
First you need to specify the area 1 where we need the virtual-link which is area 1 in my example. Second step is to configure the OSPF router ID of the other ABR. Keep this in mind…you need to configure the OSPF router ID and NOT the IP address of the ABR.
What is P and N bit in OSPF?
This bit position has two roles: N-bit: this one is used in hello packets for OSPF NSSA routers. When the N-bit is not supported, the routers won’t become neighbors. P-bit: this one is only used in the NSSA external LSA header.
What does an OSPF area contain?
An OSPF area contains one set of link-state information, although each router within the area will process that information individually to form its own SPF tree. OSPF process IDs are locally significant and are created by the administrator.
Why is multi area OSPF used?
The reason you would create multiple area types is to avoid overwhelming routers with a huge routing table and topology database when they do not need to understand this information. To reduce router overhead in a large OSPF network, you can create different types of areas.
How does virtual link work in OSPF autonomous system?
All areas in an OSPF autonomous system must be physically connected to the backbone area (area 0). In some cases where this physical connection is not possible, you can use a virtual link to connect to the backbone through a non-backbone area. You can also use virtual links to connect two parts of a partitioned backbone through a non-backbone area.
Can a link belong to more than one OSPF area?
Both sides of any link always belong to the same OSPF area. An autonomous system boundary router (ASBR) advertises external destinations throughout the OSPF autonomous system. External routes are the routes redistributed into OSPF from any other protocol.
Can a virtual link be used in a non-backbone area?
In some cases, where this is not possible, you can use a virtual link to connect to the backbone through a non-backbone area. You can also use virtual links to connect two parts of a partitioned backbone through a non-backbone area. The area through which you configure the virtual link, known as a transit area, must have full routing information.
What is an ” area ” in OSPF configuration?
An OSPF network can be divided into sub-domains called areas. An area is a logical collection of OSPF networks, routers, and links that have the same area identification.