Dell PowerSwitch S4820T 9.50.1 Configuration Guide for the S4820T System - Page 335
Configuring the Hash Algorithm Seed, Link Bundle Monitoring
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CONFIGURATION mode. ipv6 ecmp-deterministic Configuring the 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 behavior means that for a given flow, even though the prefixes are sorted, two unrelated chassis can select different hops. Dell Networking OS provides a command line interface (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 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. NOTE: If you remove the hash algorithm configuration, the hash seed does not return to the original factory default setting. To configure the hash algorithm seed, use the following command. • Specify the hash algorithm seed. CONFIGURATION mode. hash-algorithm seed value [stack-unit number] [port-set number] The range is from 0 to 4095. Link Bundle Monitoring Link bundle monitoring is supported on the S4820T platform. Monitoring linked ECMP bundles allows traffic distribution amounts in a link to be monitored for unfair distribution at any given time. A default threshold of 60% is defined as an acceptable amount of traffic on a member link. Links are monitored in 15-second intervals for three consecutive instances. Any deviation within that time causes a syslog to be sent and an alarm event to be generated. When the deviation clears, another syslog is sent and a clear alarm event is generated. for example Link bundle monitoring percent threshold %STKUNIT0-M:CP %IFMGR-5-BUNDLE_UNEVEN_DISTRIBUTION: Found uneven distribution in LAG bundle 11.. The link bundle utilization is calculated as the total bandwidth of all links divided by the total bytes-persecond of all links. Within each ECMP group, interfaces can be specified. If monitoring is enabled for the ECMP group, the utilization calculation is performed when the utilization of the link-bundle (not a link within a bundle) exceeds 60%. Enable link bundle monitoring using the ecmp-group command. Equal Cost Multi-Path (ECMP) 335
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