Network load balancing: Difference between revisions

Revision as of 17:48, 30 March 2023

Revision as of 07:45, 19 June 2025

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=== Multicast mode ===

Another option is to make NLB in [[Multicast routing protocol|multicast]] mode. The unicast [[IPv4]] address of the cluster is linked to a [[multicast]] MAC address. The hosts is in the cluster will never send traffic to the [[Network switch|switch]] using this MAC address with the cluster IPv4 address so one would need to create a static [[Address Resolution Protocol|ARP]] entry on the router (layer 3) in the attached network. Not all vendors will allow you to create an ARP entry where you use a unicast IP address and a multicast MAC address. Cisco publishes some examples how to set up MS NLB on Catalyst switches running [[IOS]]<ref>Cisco: [http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a0080a07203.shtml Catalyst configuration examples] {{webarchive|url=https://web.archive.org/web/20140131115541/http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a0080a07203.shtml |date=2014-01-31 }}, visited 8 June 2013</ref> and these same examples can be used for switches from many other vendors. As with NLB in unicast mode: incoming traffic towards the cluster will be flooded to all ports in the switch/VLAN and not all vendors support this setup. To limit the flooding, MS NLB now supports IGMP which should lead to the switches learning which ports are actually using the [[multicast address]],<ref>Microsoft Support knowledge base: [http://support.microsoft.com/kb/283028 KB283028: IGMP Snooping support on NLB], visited 8 June 2013</ref> but it doesn't always lead to the desired result. For example, [[Dell PowerConnect]] [[multi-layer switchesswitch]]es officially don't support MS NLB in multicast. Even though it does work, it will lead to high CPU utilization - affecting (other) traffic in the switch<ref>Dell Tech Communities:[http://en.community.dell.com/support-forums/network-switches/f/866/p/19435793/20091643.aspx Trying to limit switch flooding from a Microsoft Windows Network Load Balacing (NLB)] {{Webarchive|url=https://web.archive.org/web/20131005003853/http://en.community.dell.com/support-forums/network-switches/f/866/p/19435793/20091643.aspx |date=2013-10-05 }}, February 2012. Visited: 8 June 2013</ref> and on other switches one might have other limitations such that the switch to which the NLB NICs are connected can't be the same switch that does the IP routing.

== Server load balancing ==