Technical Documentation

Overview of Per-Packet Load Balancing

By default, when there are multiple equal-cost paths to the same destination for the active route, the Junos OS uses a hash algorithm to choose one of the next-hop addresses to install in the forwarding table. Whenever the set of next hops for a destination changes in any way, the next-hop address is rechosen using the hash algorithm.

You can configure the Junos OS so that, for the active route, all next-hop addresses for a destination are installed in the forwarding table. This feature is called per-packet load balancing. You can use load balancing to spread traffic across multiple paths between routers. The behavior of the load-balance per-packet function depends on the version of the Internet Processor application-specific integrated circuit (ASIC) in your routing platform:

  • On routing platforms with the Internet Processor ASIC, when per-packet load balancing is configured, traffic between routers with multiple paths is spread using the hash algorithm across the available interfaces. The forwarding table balances the traffic headed to a destination, transmitting it in round-robin fashion among the multiple next hops (up to a maximum of eight equal-cost load-balanced paths). The traffic is load-balanced on a per-packet basis.
  • On routing platforms with the Internet Processor II ASIC, when per-packet load balancing is configured, traffic between routers with multiple paths is divided into individual traffic flows (up to a maximum of 16 equal-cost load-balanced paths). Packets for each individual flow are kept on a single interface.

Note: You can configure per-packet load balancing to optimize VPLS traffic flows across multiple paths.

For information about configuring per-packet load balancing, see the following topics:

Related Topics

Published: 2010-07-16

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