Shulou(Shulou.com)06/03 Report--

What is a virtual link?

Virtual connection refers to a logical connection channel established between two ABR through a non-backbone area (transition region-Transit Area), which can be understood as a point-to-point connection between two ABR. " Logical channel "means that multiple routers running OSPF between two ABR only play the role of forwarding a message (because the destination address of the protocol message is not these routers, so these messages are transparent to them, they are only forwarded as ordinary IP messages), and routing information is transmitted directly between the two ABR. The routing information here refers to the LSA of the type3 generated by ABR, and the synchronization mode of the router in the area has not changed.

Virtual connection (Virtual-link): because of the complex topology of the network, sometimes it can not meet the requirement that each area must be directly connected to the backbone area. In order to solve this problem, OSPF put forward the concept of virtual link.

A virtual connection is set between two routers, both of which have a port connected to the same non-backbone area. Virtual connections are considered to belong to the backbone area. In the OSPF routing protocol, two routers at both ends of the virtual connection are connected by a point-to-point link. In OSPF routing protocol, routing information through virtual connections is treated as intra-domain routing.

Command

Router (config-router) # area area-id virtual-link router-id

Where area-id is the area passed by virtual links.

Router-id refers to the arriving router id

Experiment

Configure the following topology in GNS3

1. Configure the IP address of PC

two。 Configure the R1 port IP, set the R1 router-id, and declare the network segment in area 2

3. Configure R2: set port IP, declare network segment in area1 and area2, and create virtual link

4. Configure R3: set port IP, declare network segment in area1 and area0, create virtual link

5. Configure R4: Port IP, set the router-id of R1, and declare the network segment in area 0

6. Test whether it is interoperable

The experiment was successful

Summary

In the process of configuring ospf virtual links, we should pay attention to that it is very important and easy to make mistakes to declare the router id of the target area when setting up a virtual link from one area to another. This is a very critical problem, not because of a moment of carelessness lead to the failure of the experimental results!

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