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Table Of Contents
Equal Cost Multi-Path (ECMP)
Equal cost multi-path (ECMP) is supported on Dell Networking OS.
Topics:
ECMP for Flow-Based Affinity
Configuring the Hash Algorithm
Enabling Deterministic ECMP Next Hop
Configuring the Hash Algorithm Seed
Link Bundle Monitoring
Managing ECMP Group Paths
Creating an ECMP Group Bundle
Modifying the ECMP Group Threshold
ECMP for Flow-Based Affinity
IPv6 /128 routes having multiple paths do not form ECMPs. The /128 route is treated as a host entry and finds its place in the
host table.
NOTE:
Using XOR algorithms result in imbalanced loads across an ECMP/LAG when the number of members in said
ECMP/LAG is a multiple of 4.
Flow-based affinity includes the following:
Configuring the Hash Algorithm Seed
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
Dell EMC Networking OS Behavior: In the Dell EMC Networking OS versions prior to 8.2.1.2, the ExaScale default hash-
algorithm is 0. Beginning with Dell EMC Networking OS 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 sorts 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.
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