OSPF Virtual link interrupt Detection Mechanism

1) OSPF Neighbor Relationship interruption

It does not trigger Goodbye message, bgp notification message

In OSPF, neighbors cannot explicitly interrupt the neighbor relationship through a message. Inactivity Timer is used to prevent the generation of the unilateral neighbor relationship.

In OSPF Virtual links, once a neighbor relationship is established, Hello messages are no longer sent cyclically, and the neighbor relationship never times out. Therefore, an additional mechanism is required to detect the interruption at one end of the virtual link.

2) virtual link interruption Detection

When one end of the virtual link is interrupted, the device will send a Router-LSA to the transmission area, where the flag V will be reset. The significance of flag V can be reviewed. The message structure of Router-LSA)

After the peer end of the virtual link receives the extensive Router-LSA, it detects that the vbit is reset, that is, the virtual link is interrupted, and the virtual link is immediately disconnected locally, and the Router-LSA is sent, the flag V is also reset.

3) Case studies

650) this. length = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/0421194610-0.png "title =" Unnamed image .png "width =" 700 "height =" 118 "border =" 0 "hspace =" 0 "vspace =" 0 "style =" width: 700px; height: 118px; "alt =" 080451974.png"/>

As shown in, when the virtual Link at R3 is interrupted, R3 cannot send the Router-LSA in Area 0 to delete the Link because R3 is no longer an ABR.

R3 then sends the Router-LSA of Area 1, where v bit is set to 0. When R2 receives the LSA, it immediately terminates the Virtual Link joining relationship, sends Area1 Router-LSA, and sets v bit to 0. Sends Area 0 Router-LSA and deletes the link: Virtual-Link

Note:

R2 is not the origin Device of Area 2 LSA and is not authorized to clear these LSA. Therefore, although R3 cannot be reached in Area 0, the LSA advertised by R3 remains in the LSDB of each device in Area 0.

If R2 breaks the Virtual Link, R2 will send Area 0 Router-LSA and delete link: Virtual-Link; R2 will also send Area 1Router-LSA because it is still an ABR, reset the vbit to interrupt the virtual link joining relationship.

This article is from the "Thely" blog, please be sure to keep this source http://thely.blog.51cto.com/2695427/1302403