Load Balancing Among OSPF Routes

Conditions

If the maximum number of OSPF routes that can be used to load-balance traffic and the maximum number of routes of all types that can be used to load-balance traffic are both greater than 1 and multiple OSPF routes with the same prefix exist, these routes participate in load balancing only when the following conditions are met:

• These routes are of the same type (intra-area, inter-area, Type-1 external, or Type-2 external).
• These routes have different direct next hops.
• These routes have the same cost.
• If these routes are Type-2 external routes, the costs of the links to the ASBR or forwarding address are the same.
• If OSPF route selection specified in relevant standards is implemented, these routes have the same area ID.

The OSPF route selection rules specified in relevant standards are different from those in relevant standards. By default, Huawei NetEngine 8000 F perform OSPF route selection based on the rules specified in relevant standards. To implement OSPF route selection based on the rules specified in relevant standards, run the undo rfc1583 compatible command.

Principles

If the number of OSPF routes available for load balancing is greater than the configured maximum number of OSPF routes that can be used to load-balance traffic, OSPF selects routes for load balancing in the following order:

1. Routes whose next hops have smaller weights

   

   Weight indicates the route preference, and the weight of the next hop can be changed by the nexthop command (in OSPF view). Routing protocols and their default preferences:

   • DIRECT: 0
   • STATIC: 60
   • IS-IS: 15
   • OSPF: 10
   • OSPF ASE: 150
   • OSPF NSSA: 150
   • RIP: 100
   • IBGP: 255
   • EBGP: 255

2. Routes whose outbound interfaces have larger indexes

   

   Each interface has an index, which can be seen in the display interface interface-name command in any view.
3. Routes whose next hop IP addresses are larger.