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IP Hash-Based Load Balancing and EtherChannel

On a standard vSwitch, IP Hash (the out-IP policy) uses the source and destination IP addresses to calculate a hash.

It is the only policy which allows the VM to access two physical adapters without having two virtual NICs.

Requirements are:

  • all physical network adapters must be connected to the same switch
  • OR if connecting to two switches, link aggregation across physical switches must be used to ‘stack’ the switches
  • the switch must be configured for link aggregation (802.3ad) / EtherChannel
  • for EtherChannel to work across two physical Cisco switches, MEC (Multichassis EtherChannel) must be used on 6500 or Virtual Port Channel (vPC) on Cisco Nexus 7000. See here for more info.
  • all physical NICs must be set to active, instead of having some active, some passive

Note: although it can more evenly spread the transfer traffic for a single VM, it does not provide a benefit for large data transfers occurring between the same source and dest IPs.

See also:

Host requirements for link aggregation for ESX and ESXi (1001938)

Sample configuration of EtherChannel / Link Aggregation Control Protocol (LACP) with ESXi/ESX and Cisco/HP switches (1004048)

Troubleshooting IP-Hash outbound NIC selection (1007371)

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