H3C Technologies H3C S7500E Series Switches - Manual (Page 87)

4-18
Figure 4-20 NSSA external LSA format
Supported OSPF Features
Multi-process
With multi-process support, multiple OSPF processes can run on a router simultaneously and
independently. Routing information interactions between different processes seem like interactions
between different routing protocols. Multiple OSPF processes can use the same RID.
An interface of a router can only belong to a single OSPF process.
Authentication
OSPF supports authentication on packets. Only packets that pass the authentication are received. If
hello packets cannot pass authentication, no neighbor relationship can be established.
The authentication type for interfaces attached to a single area must be identical. Authentication types
include non-authentication, plaintext authentication and MD5 ciphertext authentication. The
authentication password for interfaces attached to a network segment must be identical.
Hot Standby
Distributed routers support OSPF Hot Standby (HSB). OSPF backups necessary information of the
Active Main Board (AMB) into the Standby Main Board (SMB). Once the AMB fails, the SMB begins to
work to ensure the normal operation of OSPF.
OSPF backups the OSPF configuration information to the SMB. Once the AMB fails, OSPF will
perform Graceful Restart (GR), obtaining adjacencies from and synchronizing the Link State Database
with neighbors.
The Graceful Restart feature is mainly used for High Availability (HA) and does not interfere with any
other routers.
When a router shuts down, its neighbors will delete it from their neighbor tables and inform other
routers, resulting in SPF recalculation. If the router restarts in several seconds, it is unnecessary to
perform SPF recalculation, and reestablish adjacencies.
To avoid unnecessary SPF calculation, when a router restarts, it will inform neighboring routers the
shutdown is temporary. Then these routers will not delete the router from their neighbor tables, and
other routers have no idea about this restart.