VCS uses private network communications between cluster nodes for cluster maintenance. The Low Latency Transport functions as a high-performance, low-latency replacement for the IP stack, and is used for all cluster communications. Symantec recommends at least two independent networks between all cluster nodes.
For detailed information on the setting up networks, see Cluster Server Configuration and Upgrade Guide.
These networks provide the required redundancy in the communication path and enable VCS to differentiate between a network failure and a system failure.
LLT has the following two major functions:
LLT distributes (load balances) internode communication across all available private network links. This distribution means that all cluster communications are evenly distributed across all private network links (maximum eight) for performance and fault resilience. If a link fails, traffic is redirected to the remaining links.
LLT is responsible for sending and receiving heartbeat traffic over network links. The Group Membership Services function of GAB uses this heartbeat to determine cluster membership.