Transparent Interconnection of Lots of Links (TRILL) is the Internet Engineering Task Force’s specification for enabling multipathing in the data center.
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TRILL applies network layer routing protocols to the link layer and -- with knowledge of the entire network -- uses that information to support Layer 2 multipathing. This enables multi-hop Fibre Channel over Ethernet (FCoE), reduces latency and improves overall network bandwidth utilization.
TRILL, which is undergoing IETF’s standardization process, is meant to replace the spanning tree protocol (STP). STP, which was created to prevent bridge loops, only allows one path between network switches or ports. When a network segment goes down, an alternate path is chosen and this process can cause unacceptable delays in a data center network. TRILL is designed to address this problem by applying the Intermediate System-to-Intermediate System protocol (IS-IS) Layer 3 routing protocol to Layer 2 devices. This essentially allows Layer 2 devices to route Ethernet frames.
Proponents of TRILL claim that by getting rid of STP and freeing up more Layer 2 paths, enterprises will be better able to migrate virtual machines (VMs) across the data center network. There will also be more bandwidth available for intensive applications like real-time communications (RTC) and for the transport of storage traffic across the Ethernet network with FCoE and iSCSI. In addition, TRILL will make switches more cost-effective because it will allow enterprises to use more links in their data center network designs. It will also allow switches to load balance traffic over multiple Layer 2 links. However, some experts don’t agree that TRILL will solve the problems associated with STP or that a replacement protocol is needed at all. Some claim that TRILL might actually lead to poor data center network design techniques and that other approaches such as shortest path bridging (SPB) or multichassis link aggregation (MLAG) can do the job better.