Service Manual

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 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:
Equal Cost Multi-Path (ECMP)
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