Dell S4820T, Configuration Manual

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15
Equal Cost Multi-Path (ECMP)
This chapter describes configuring ECMP.
ECMP for Flow-Based Affinity
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
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
Equal Cost Multi-Path (ECMP)
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