Dell Force10 E600i FTOS Version 8.4.1.5 Configuration Guide for ExaScale - Page 326
Configurable Hash Algorithm Seed
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www.dell.com | support.dell.com With 8 or less ECMPs, the ordering is lexicographic and deterministic. With more than 8 ECMPs, ordering is deterministic, but it is not in lexicographic order. Task Command Syntax Command Mode Enable IPv4 Deterministic ECMP Next Hop. ip ecmp-deterministic CONFIGURATION Enable IPv6 Deterministic ECMP Next Hop. ipv6 ecmp-deterministic CONFIGURATION Note: Packet loss might occur when you enable ip/ipv6 ecmp-deterministic for the first-time only. Configurable Hash Algorithm Seed 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. Note: While the seed is stored separately on each port-pipe, the same seed is used across all CAMs. Note: You cannot separate LAG and ECMP, but you can use different algorithms across 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. Note: If the hash algorithm configuration is removed. Hash seed will not go to original factory default setting. Task Command Syntax Specify the hash algorithm seed. hash-algorithm seed value [linecard number] [port-set number] Range: 0 - 4095 Command Mode CONFIGURATION In Figure 17-1, Core Router 1 is an E-Series TeraScale and Core Router 2 is an E-Series ExaScale. They have similar configurations and have routes for prefix P with two possible next-hops. When Deterministic ECMP is enabled and the hash algorithm and seed are configured the same, each flow is consistently sent to the same next hop even though they are routed through two different chassis. 326 | Equal Cost Multi-Path
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