Description

The LAG hashing algorithm on SRX determines the member link to be used for an incoming packet. This article lists the default packet fields used by the hashing algorithm for a link aggregation group (LAG).

Solution

Junos OS uses flow-session based load balancing algorithm for load balancing across LAG interfaces.

The hash is based on:

  • SrcIP
  • DstIP
  • Protocol
  • SrcPort
  • DestPort
  • Incoming Interface index
  • Type of service(ToS)

The default option is to use Layer 3 header for load balancing hash.

The Layer 4 header can also be configured for load balancing hash with the command: 

root@SRX-node0# set forwarding-options hash-key family inet ?
Possible completions:
+ apply-groups         Groups from which to inherit configuration data
+ apply-groups-except  Don't inherit configuration data from these groups
> layer-3              Include Layer 3 (IP) data in the hash key
> layer-4              Include Layer 4 (TCP or UDP) data in the hash key

Modification History

2020-10-15: Changed per-packet to flow-session based in the solution.

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