Administrator Guide

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
Dell(conf)#
• Packet Header parameters for the rst 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 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 conguration such as ingress and egress port numbers.
• RTAG7 hashing also provides options to select between multiple hash algorithms that would result in balanced trac distribution for
various trac patterns.
Dell(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]
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 trac polarization
issues by ensuring proper ow distribution between ECMP members in the higher layers of a multi-tier network. It facilitates a dynamic
hash function selection across dierent nodes in the network on a macro ow 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 trac
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 trac over multiple paths towards its destination. In a multi-tier network where
load balancing is performed at each tier, static hash algorithms polarize the trac where load balancing is ineective in the higher tiers. The
polarization eect is exaggerated if all the nodes in the network have to choose from the same set of ECMP paths. Trac polarization
results in packet reordering and route apping. The following gure explains the trac polarization eect. Router B performs the same hash
as router A and all the trac goes through the same path to router D, while no trac is redirected to router E. The following gure explains
the trac polarization eect:
Equal Cost Multi-Path (ECMP)
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