Symmetric Hash support for ECMP. Symmetric hash need the hashing field must be symmetric. For example, packet 1 and packet 2 are symmetric in table 1 and table 2 as below, and then packet 1 and packet2 will go out from the same physical port. Now Our symmetric Hash use IP layer and L4 field to hash when packets are transmitted on ECMP. Only matching symmetric condition, two packets can be transmitted on the same member port of ECMP. 

IP PacketSource IP AddressDestination IP Address
Packet110.1.1.120.1.1.1
Packet220.1.1.110.1.1.1

                                 Table 1.

Layer 4 PacketSource IP AddressDestination IP AddressSource Port NumberDestination Port Number
Packet110.1.1.120.1.1.1100200
Packet220.1.1.110.1.1.1200100

                                Table 2.

Symmetric Hash field as below:

  1. ip-source
  2. ip-destination
  3. port-source
  4. port-destination

By default, Enable hash field on ECMP:

  1. ip-source
  2. ip-destination
  3. port-source
  4. port-destination


Symmetric hashing is supported on Helix4 , Trident2, Trident2+, Trident3 and Tomahawk platform switches.


ECMP Configuration

set interface ecmp hash-mapping symmetric true

ECMP Examples:

configure three ECMP route:

set interface gigabit-ethernet te-1/1/1 family ethernet-switching native-vlan-id 199
set interface gigabit-ethernet te-1/1/2 family ethernet-switching native-vlan-id 299
set interface gigabit-ethernet te-1/1/3 family ethernet-switching native-vlan-id 300
set interface gigabit-ethernet te-1/1/4 family ethernet-switching native-vlan-id 301
set protocols static route 100.100.100.0/24 next-hop 182.168.1.100
set protocols static route 100.100.100.0/24 next-hop 183.168.1.100
set protocols static route 100.100.100.0/24 next-hop 184.168.1.100
set protocols static route 172.168.1.0/24 next-hop 182.168.1.100
set protocols static route 172.168.1.0/24 next-hop 183.168.1.100
set protocols static route 172.168.1.0/24 next-hop 184.168.1.100
set l3-interface vlan-interface vlan199 address 172.168.1.1 prefix-length 24
set l3-interface vlan-interface vlan299 address 182.168.1.1 prefix-length 24
set l3-interface vlan-interface vlan300 address 183.168.1.1 prefix-length 24
set l3-interface vlan-interface vlan301 address 184.168.1.1 prefix-length 24
set l3-interface vlan-interface vlan399 address 100.100.100.1 prefix-length 24
set vlans vlan-id 199 l3-interface "vlan199"
set vlans vlan-id 299 l3-interface "vlan299"
set vlans vlan-id 300 l3-interface "vlan300"
set vlans vlan-id 301 l3-interface "vlan301"
set vlans vlan-id 399 l3-interface "vlan399"

Configure the symmetric hash true

set interface ecmp hash-mapping symmetric true