Reference Guide

14
Equal Cost Multi-Path (ECMP)
Equal cost multi-path (ECMP) is supported on theS4820T platform.
ECMP for Flow-Based Affinity
ECMP for flow-based affinity is available on theS4820T platform.
Flow-based affinity includes the following:
• Link Bundle Monitoring
Configuring the Hash Algorithm
TeraScale has one algorithm that is used for link aggregation groups (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.
• Change the ExaScale hash-algorithm for LAG, ECMP, and NH-ECMP to match TeraScale.
CONFIGURATION mode.
hash-algorithm ecmp checksum 0 lag checksum 0 nh-ecmp checksum 0
FTOS Behavior: In the Dell Networking operating system (FTOS) versions prior to 8.2.1.2, the ExaScale default hash-
algorithm is 0. Beginning with FTOS version 8.2.1.2, the default hash-algorithm is 24.
Enabling Deterministic ECMP Next Hop
Deterministic ECMP next hop arranges all ECMPs in order before writing them into the content addressable memory
(CAM).
For example, suppose the RTM learns eight ECMPs in the order that the protocols and interfaces came up. In this case,
the forwarding information base (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.
With eight or less ECMPs, the ordering is lexicographic and deterministic. With more than eight ECMPs, ordering is
deterministic, but it is not in lexicographic order.
To enable deterministic ECMP next hop, use the appropriate command.
NOTE: Packet loss might occur when you enable ip/ipv6 ecmp-deterministic for the first-time only.
• Enable IPv4 Deterministic ECMP Next Hop.
CONFIGURATION mode.
ip ecmp-deterministic
• Enable IPv6 Deterministic ECMP Next Hop.
CONFIGURATION mode.
ipv6 ecmp-deterministic
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