Equal Cost Multi-Path (Ecmp); Ecmp For Flow-Based Affinity; Configuring The Hash Algorithm; Enabling Deterministic Ecmp Next Hop - Dell S4820T Configuration Manual

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Equal Cost Multi-Path (ECMP)

Equal cost multi-path (ECMP) is supported on Dell Networking OS.

Flow-based affinity includes the following:

Link Bundle Monitoring

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 Networking OS Behavior: In the Dell Networking OS versions prior to 8.2.1.2, the ExaScale default

hash-algorithm is 0. Beginning with Dell Networking OS version 8.2.1.2, the default hash-algorithm is 24.

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

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-

Enable IPv4 Deterministic ECMP Next Hop.

CONFIGURATION mode.

ip ecmp-deterministic

Enable IPv6 Deterministic ECMP Next Hop.

CONFIGURATION mode.

ipv6 ecmp-deterministic

Equal Cost Multi-Path (ECMP)