Administrator Guide

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 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:
Figure 37. Before 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.
Some of the anti-polarization techniques used generally to mitigate unequal traffic distribution in LAG/ECMP as follows:
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Equal Cost Multi-Path (ECMP)