Reference Guide

Equal Cost Multi-Path | 325
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Equal Cost Multi-Path
ECMP for Flow-based Affinity
ECMP for Flow-based Affinity is available only platform: e
The hashing algorithm on E-Series TeraScale and E-Series ExaScale are different. Hashing on ExaScale is
based on CRC, checksum, or XOR, and the algorithm on TeraScale is based on checksum only. If
flow-based affinity is to be maintained by an ExaScale and TeraScale chassis, they must both use the same
hashing algorithm and seed value, and ECMP must deterministically choose a next hop.
• Configurable Hash Algorithm
• Configurable Hash Algorithm Seed
• Deterministic ECMP Next Hop
Configurable Hash Algorithm
TeraScale has one algorithm that is used for LAGs, ECMP, and NH-ECMP, and ExaScale can use three
different algorithms for each of these features. To adjust the ExaScale behavior to match TeraScale, use the
following command:
Deterministic ECMP Next Hop
Deterministic ECMP Next Hop arranges all ECMPs in order before writing them into the CAM. For
example, suppose the RTM learns 8 ECMPs in the order that the protocols and interfaces came up. In this
case, the FIB and CAM sort them so that the ECMPs are always arranged.This implementation ensures that
every chassis having the same prefixes orders the ECMPs the same.
Task Command Syntax Command Mode
Change the ExaScale hash-algorithm for LAG,
ECMP, and NH-ECMP to match TeraScale.
hash-algorithm ecmp checksum 0 lag
checksum 0 nh-ecmp checksum 0
CONFIGURATION
FTOS Behavior: In FTOS versions prior to 8.2.1.2, the ExaScale default hash-algorithm is 0.
Beginning with version 8.2.1.2, the default hash-algorithm is 24.