Dell EMC Configuration Guide for the S4048T–ON System 9.14.2.4

RTAG7

RTAG7 is a hashing algorithm that load balances the traffic within a trunk group in a controlled manner. In order to effectively increase the bandwidth of the LAG/Equal Cost Multiple Path routes, traffic is balanced across the member links. The balancing is performed by using the RTAG7 hashing, which is designed to have the member links used efficiently as the traffic profile gets more diverse.Hashing-based load balancing is used in the following applications:

• L3 ECMP
• LAGs
• HiGig trunking

The RTAG7 hash scheme generates a hash that consists of the following two portions:

• The first portion is primarily generated from packet headers to identify micro-flows in the traffic. The Parameters that are considered for hash computations by default in RTAG7 hashing is shown in the given example:

  DellEMC#show load-balance
  Load-Balancing Configuration For LAG & ECMP:
  --------------------------------------------
  IPV4 Load Balancing Enabled
  IPV4 FIELDS : source-ipv4 dest-ipv4 vlan protocol L4-source-port L4-dest-port
  
  IPV6 Load Balancing Enabled
  IPV6 FIELDS : source-ipv6 dest-ipv6 vlan protocol L4-source-port L4-dest-port
  
  Mac Load Balancing Enabled
  MAC FIELDS : source-mac dest-mac vlan ethertype
  
  Load Balancing Configuration for tunnels
  ipv4-over-ipv4 Payload header
  ipv4-over-ipv6 Payload header
  ipv6-over-ipv6 Payload header
  ipv6-over-ipv4 Payload header
  ipv4-over-gre-ipv4 Payload header
  ipv6-over-gre-ipv4 Payload header
  ipv4-over-gre-ipv6 Payload header
  ipv6-over-gre-ipv6 Payload header
  
  mac-in-mac header based hashing is disabled
  TcpUdp Load Balancing  Enabled
  DellEMC(conf)#

• Packet Header parameters for the first portion of the RTAG7 hash can be controlled. By default, all the listed parameters from the Packet header are considered for hash computation. Few parameters [on demand] can be removed using the given CLIs.

  DellEMC(conf)#load-balance ?
  flexhash                Enable flexhash based on IP Protocol
  ingress-port            Option to Source Port Id for ECMP/LAG hashing
  ip-selection            Set the IPV4 key fields to use in hash computation(default = source-ip dest-ip vlan protocol L4-source-port L4-dest-port)
  ipv6-selection          Set the IPV6 key fields to use in hash computation(default = source-ipv6 dest-ipv6 vlan protocol L4-source-port L4-dest-port)
  mac                     Set the mac key fields to use in hash computation(default = source-mac dest-mac vlan ethertype)
  tcp-udp                 Option to use TCP/UDP ports in packet for ECMP/LAG hashing
  tunnel                  Set the tunnel key fields to use in hash computation(default = Hash-computation based on Inner Header)]

• The second portion comes from static physical configuration such as ingress and egress port numbers.
• RTAG7 hashing also provides options to select between multiple hash algorithms that would result in balanced traffic distribution for various traffic patterns.

  DellEMC(conf)#hash-algorithm ecmp ?
  crc16                   CRC16_BISYNC - 16 bit CRC16-bisync polynomial
  crc16cc                 CRC16_CCITT - 16 bit CRC16 using CRC16-CCITT polynomial
  crc32LSB                CRC32_LOWER - LSB 16 bits of computed CRC32
  crc32MSB                CRC32_UPPER - MSB 16 bits of computed CRC32(default)
  crc-upper               Use Upper 32 bits of key for hash computation
  flow-based-hashing      Enable flow based hashing
  dest-ip                 Use Destination IP for ECMP hashing
  lsb                     Always return the LSB of the key as the hash
  xor1                    CRC16_BISYNC_AND_XOR1 - Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor1
  xor2                    CRC16_BISYNC_AND_XOR2 - Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor2
  xor4                    CRC16_BISYNC_AND_XOR4 - Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor4
  xor8                    CRC16_BISYNC_AND_XOR8 - Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor8
  xor16                   CR16 - 16 bit XOR]