Users Guide

Equal Cost Multi-Path (ECMP)

This chapter describes configuring ECMP. This chapter describes configuring ECMP.

Topics:

• ECMP for Flow-Based Affinity

• Link Bundle Monitoring

• RTAG7

• Flow-based Hashing for ECMP

ECMP for Flow-Based Affinity

ECMP for flow-based affinity includes 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 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.

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.

• Enable IPv4 Deterministic ECMP next hop.

CONFIGURATION mode.

ip ecmp-deterministic

• Enable IPv6 Deterministic ECMP next hop.

CONFIGURATION mode.

ipv6 ecmp-deterministic

266 Equal Cost Multi-Path (ECMP)