Planet XGS3-24042 User Manual download pdf (Page 398)

100

101

47-16

Chapter 47 OSPF GR

47.1 Introduction to OSPF GR

OSPF Graceful-Restart（short for OSPF GR）， is used to maintain data forwarding correctly and flow of crucial

service is not interrupted when routing protocol restarts or switchover of layer 3 switches between active

master and standby master. It is one of high availability technologies.

So far, the high layer 3 switches usually adopt a design for separating control and forwarding. The control

module for counting routing protocol at master control board, but data forwarding module is at liner card. As a

result, it will not affect data forwarding on line card when the master control board is restarted. So the device

supporting GR is generally a chassis device and has two master control boards.

Since standard OSPF protocol (RFC2328) does not support GR, it will lead to flow cut off and routing surge

when routing protocol is restarted or switchover between active master and standby master for various

reasons. For example, as shown in below figure, when S1 occurs switchover, the neighborhood relation

between S1 and S2 will lose, at that time S2 will send Router-LSA to S3 and S4 and this LSA does not include

the link between S1 and S2. After S3 and S4 received LSA, they will count routing protocol again. The result

will not include the link between S1 and S2. After S1 finishes the switchover, it will establish neighborhood

relation with S2 and synchronize database, this action leads S2, S3 and S4 to count routing again. However,

switchover of S1 will result routing shiver, which is not accepted by some networks with high requirement for

performance.

Figure 47-1 typical application scene

OSPF GR described in RF C3623 is come up for the above state. Its basic idea is that if the network topology

keeps stabilization during the switchover and layer 3 switch can maintain the same forwarding list, then its

neighbor can maintain their relationship, which can make the switch on its forwarding path still. If S1 and S2

support and enable GR, the liner card of S1 will keep the traffic forwarding and S2 can maintain the

relationship with S1, at the same time, network topology between S3 and S4 will not be changed, furthermore,

it does not need to count routing again. All of these ensure the traffic forwarding and avoid routing shiver.

Layer 3 switch can be divided into GR restarter and GR helper according to its function in GR process. GR

restarter is layer 3 switch to occur the switchover between active master and standby master or restart

1 2 ... 393 394 395 396 397 398 399 400 401 402 403 ... 720 721

Comments to this Manuals

No comments

Planet XGS3-24042 User Manual Page 398

Comments to this Manuals

Related products and manuals for Routers Planet XGS3-24042