Flow-Based Hashing For Ecmp - Dell S4048–ON Configuration Manual

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
Dell(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.
Dell(conf)#load-balance ?
flexhash
ingress-port
ip-selection
ip dest-ip vlan protocol L4-source-port L4-dest-port)
ipv6-selection
ipv6 dest-ipv6 vlan protocol L4-source-port L4-dest-port)
mac
mac dest-mac vlan ethertype)
tcp-udp
tunnel
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.
Dell(conf)#hash-algorithm ecmp ?
crc16
crc16cc
crc32LSB
crc32MSB
crc-upper
flow-based-hashing
dest-ip
lsb
xor1
of xor1
xor2
of xor2
xor4
of xor4
xor8
of xor8
xor16

Flow-based Hashing for ECMP

Flow-based hashing is one of RTAG7 hashing techniques to cater to ECMP routing in multi-tier networks. It addresses traffic polarization
issues by ensuring proper flow distribution between ECMP members in the higher layers of a multi-tier network. It facilitates a dynamic
hash function selection across different nodes in the network on a macro flow basis, by reducing route starvation and the unfair distribution
of bandwidth between members.
Polarization
Multipath routing is a method that is often used to address data forwarding issues during network failures so that the network traffic
reaches its desired destination. Multipath routing in IP networks is typically implemented using Equal-Cost Multipath (ECMP) routing,
which employs load balancing algorithms to distribute the traffic over multiple paths towards its destination. In a multi-tier network where
load balancing is performed at each tier, static hash algorithms polarize the traffic where load balancing is ineffective in the higher tiers. The
polarization effect is exaggerated if all the nodes in the network have to choose from the same set of ECMP paths. Traffic polarization
results in packet reordering and route flapping. The following figure explains the traffic polarization effect. Router B performs the same hash
as router A and all the traffic goes through the same path to router D, while no traffic is redirected to router E. The following figure explains
the traffic polarization effect:
Enabled
Enable flexhash based on IP Protocol
Option to Source Port Id for ECMP/LAG hashing
Set the IPV4 key fields to use in hash computation(default = source-
Set the IPV6 key fields to use in hash computation(default = source-
Set the mac key fields to use in hash computation(default = source-
Option to use TCP/UDP ports in packet for ECMP/LAG hashing
Set the tunnel key fields to use in hash computation(default = Hash-
CRC16_BISYNC - 16 bit CRC16-bisync polynomial
CRC16_CCITT - 16 bit CRC16 using CRC16-CCITT polynomial
CRC32_LOWER - LSB 16 bits of computed CRC32
CRC32_UPPER - MSB 16 bits of computed CRC32(default)
Use Upper 32 bits of key for hash computation
Enable flow based hashing
Use Destination IP for ECMP hashing
Always return the LSB of the key as the hash
CRC16_BISYNC_AND_XOR1 - Upper 8 bits of CRC16-BISYNC and lower 8 bits
CRC16_BISYNC_AND_XOR2 - Upper 8 bits of CRC16-BISYNC and lower 8 bits
CRC16_BISYNC_AND_XOR4 - Upper 8 bits of CRC16-BISYNC and lower 8 bits
CRC16_BISYNC_AND_XOR8 - Upper 8 bits of CRC16-BISYNC and lower 8 bits
CR16 - 16 bit XOR]
Equal Cost Multi-Path (ECMP) 319