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Configuring LLT on windows servers - Ethernet vs UDP/IP

Created: 26 Oct 2012 • Updated: 11 Jun 2014
deepak rawal's picture
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Configuration wizard for creating a cluster provides option to setup LLT with Ethernet or UDP/IP protocol. This post provides some details on which option to choose. 

Cluster configuration wizard (VCW) detects NIC cards available for configuring LLT network links on each windows server.  Selecting NIC(s) for each server configures LLT to use Ethernet protocol.  If is important to make sure that each NIC is connected (either directly OR via a layer 2 switch) via separate network hardware for increased fault tolerance.  This is relatively easy to ascertain for Ethernet, since connection traverses a few network components. All windows servers connected to same Ethernet  are able to discover each other (ARP) dynamically.  This makes changing network configuration for cluster relatively simple. LLT traffic network overhead is low.  For large number of virtual machines hosted on a hypervisor in a datacenter, this type of configuration scales well.

Wizard (VCW) for windows server can be used to configure LLT network links over IP network.  In this scenario, IP address for each server node is required to create a point to point connection between each pair of cluster nodes.  Each IP link should use separate network hardware components (routers, switches, etc) for increased fault tolerance.  Task of setting up IP network requires little more effort vs Ethernet.  OTOH, many fold improvements in network infrastructure speeds and ability to handle larger packet sizes has made using UDP/IP for LLT quite effecient vs the Ethernet.  There are cluster configuration scenarios, where configuring LLT over UDP is the only option available (e.g. replicated data clusters over long distances).  Overall, there is a slightly higher cost, complexity and processing ovehead associated with using LLT over UDP/IP or UDP/IPv6, but due to effeciencies of modern networking infrastructure, this option has become equally viable.

To summarize, creating network links for LLT requires a bit of extra effort.  LLT protocol is able to make use of Ethernet or UDP/IPv4/IPv6 effeciently.  Ethernet connection may be easier to setup, where as UDP/IPv4/IPv6 may be necessary for your cluster configuration.