Limitations and Precautions for OSPF

Hardware Requirements

OSPF is supported by all models.

License Requirements

The OSPF function is not license-controlled.

Precautions

• To establish an OSPF neighboring relationship, devices need to exchange DD packets. DD packets are OSPF unicast packets. By default, OSPF unicast packets are forwarded under the control of security policies. Unicast packets such as DD packets or LSR packets are transmitted when the OSPF network type is broadcast or P2MP. In this case, you need to configure security policies to allow the transmission of these packets. Otherwise, the adjacency cannot reach the full state, and the adjacency cannot be established.
• The number of entries in the IP routing table is limited, but that in the OSPF LSDB and routing table is not limited. If the network where the FW resides has excessive OSPF routes, memory exhaustion and abnormal restart may occur.
• If the network where the FW resides may have excessive OSPF routes, you are advised to run the maximum-routes command to limit the number of OSPF routes to minimize the possibility of memory exhaustion. However, the number of OSPF LSDB entries cannot be limited. Therefore, memory exhaustion may still occur if the number LSDB entries is large enough, leading to unpredictable problems.
• In hot standby networking, the preemption delay of the VGMP group shall be greater than the neighbor establishment time (300 seconds). When a link fault occurs, OSPF adjacency fails to be established, which may interrupt services. The default preemption delay is 60 seconds. You can use the hrp preempt delay interval command to set the preemption delay.
• In hot standby networking, if the upstream device runs BGP, the downstream device runs OSPF, and OSPF uses default-route-advertise to generate a default route:
  • Change the BGP route priority to a value larger than 10 and smaller than 150.

    The default priority of an intra-area route is 10 (highest priority). The default route is an external route, and its default priority is 150. The default priority of a BGP route is 255 (lowest priority). If the default priority is used, the BGP route cannot take effect.

  • Configure route filtering to prevent the learning of the default downstream OSPF route.

    If the upstream device learns the default downstream route, the traffic of the upstream device cannot reach the extranet.

• In hot standby networking, you are advised to manually specify the router-id during OSPF configuration. Otherwise, the active and standby FWs may have the same router-id, causing a route calculation error.
• In hot standby networking, ensure that the routes corresponding to the services can operate in symmetric mode but not in asymmetric mode.