Ip Ecmp-Deterministic - Dell Force10 S4810P Reference Manual

Ftos command line reference guide for the s4810 system ftos 9.1.(0.0)

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Deterministic ECMP sorts ECMPs in order even though RTM provides them in a random order.

However, the hash algorithm uses as a seed the lower 12 bits of the chassis MAC, which yields

a different hash result for every chassis. This means that for a given flow, even though the

prefixes are sorted, two unrelated chassis will select different hops.

FTOS provides a CLI-based solution for modifying the hash seed to ensure that on each

configured system, the ECMP selection is same. When configured, the same seed is set for

ECMP, LAG, and NH, and is used for incoming traffic only.

ip ecmp-deterministic

Deterministic ECMP Next Hop arranges all ECMPs in order before writing them into the CAM.

ip ecmp-deterministic

Command Modes

CONFIGURATION

Command History

Version 8.3.1.0

Deterministic ECMP Next Hop arranges all ECMPs in order before writing them into the CAM.

For example, suppose the RTM learns eight ECMPs in the order that the protocols and

interfaces came up. In this case, the 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.

After enabling IPv6 Deterministic ECMP, traffic loss occurs for a few milliseconds while FTOS

sorts the CAM entries.

NOTE: While the seed is stored separately on each port-pipe, the same seed is used

across all CAMs.

You cannot separate LAG and ECMP but you can use different algorithms across the

chassis with the same seed. If LAG member ports span multiple port-pipes and line cards,

set the seed to the same value on each port-pipe to achieve deterministic behavior.

If the hash algorithm configuration is removed, the hash seed does not go to the original

factory default setting.

Introduced on the E-Series.