Load Balancing Among IS-IS Routes

Conditions

If the maximum number of IS-IS 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 IS-IS routes with the same prefix exist, these routes can participate in load balancing only when the following conditions are met:

• These routes are of the same level (Level-1, Level-2, or Level-1-2).
• These routes are of the same type (internal or external).
• These routes have the same cost.
• These routes have different direct next hops.

Principles

If the number of IS-IS routes available for load balancing is greater than the configured maximum number of IS-IS routes that can be used to load-balance traffic, IS-IS 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 IS-IS 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 with smaller neighbor IDs
3. Routes with smaller circuit IDs
4. Routes with smaller sub-network point addresses (SNPAs)

5. Routes whose outbound interfaces have smaller indexes

   

   Each interface has an index, which can be seen in the display interface interface-name command in any view.
6. Routes carrying IPv4, IPv6, and OSI next hop addresses, in descending order
7. Routes whose next hops have smaller IP addresses
8. If all the preceding items are the same, IS-IS selects the routes that are first calculated for load balancing.