FIBRE CHANNEL
FCIA
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Why TRILL The ever increasing adoption of virtual environments in data centers necessitates a more resilient L2 networking infrastructure. Efficient and reliable L2 infrastructure is needed to support the I/O demands of virtual applications especially when applications are migrated across servers or even different data centers. Today’s STP-based networks limit the available network bandwidth and fail to maintain reliable, complex network architectures. Although there may be many Equal Cost Multiple Paths (ECMPs) or physical paths through the network at any given time, all traffic will flow along the path that has been defined by
a
spanning tree that includes all network devices and nodes. By restricting traffic to this tree, loops in the logical topology are prevented at the expense of blocking alternative network paths.
While STP solves the problem of traffic loops, it prevents network capacity from being fully used. Algorithms that calculate this spanning tree may take a considerable amount of time to converge following changes in the status of the configurations. During that time, the regular flow of traffic must be halted to prevent the type of network saturation described above. Even if multiple simultaneous spanning trees are used for separate VLANs to better distribute traffic flows, the traffic in any one VLAN will still suffer from the same disadvantage of not being able to use all of the available capacity in the network. TRILL will enable multipathing for L2 networks and remove the restrictions placed on data center environments by STP single path networks. Data centers with converged networks will also benefit from the multi-hop capabilities of TRILL Routing Bridges (Rbridges) which enable multi-hop FCoE solutions.
What is TRILL To eliminate the restriction of STP single path through the network, the IETF formed a working group to study and solve this problem. In summary, the group was charged with developing a solution that:
Uses shortest path routing protocols as opposed to STP
Works at Layer 2 Supports multi-hopping environments Works with an arbitrary topology Uses an existing link-state routing protocol Remain compatible with IEEE 802.1 Ethernet networks that use STP
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What TRILL does and does not do Although TRILL can serve as an alternative to STP, it doesn’t require that STP be removed from an Ethernet infrastructure. Most networking administrators can’t, and will not, just rip and replace their current deployments just for the sake of implementing TRILL. So hybrid solutions that use both STP and TRILL are not only possible but will be the norm for at least the near term future. TRILL will also not automatically eliminate the risk of a single point of failure, especially in hybrid environments. The goals of TRILL are restricted to those listed above. Another area where TRILL is not expected to play a role is the routing of traffic across L3 routers. TRILL is expected to operate within a single subnet. While the IETF draft standard document mentions the potential for tunneling data, it is unlikely that TRILL will evolve in a way that will expand its role to cover cross L3 router traffic. Existing and well established protocols such as Multiprotocol Label Switching (MPLS) and Virtual Private LAN Service (VPLS) cover these areas and are expected to continue to do so.
Simply put, TRILL enables two primary capabilities: Multi-pathing for L2 networks Multi-hopping that will benefit FCoE configurations
Summary TRILL is a new draft standard being created by IETF to accommodate FCoE converged networks and is scheduled to be completed later this year. The goal of TRILL is to create an L2 shortest path robust multi-path and multi-hop routing protocol that eventually will replace the limited and restricted L3 STP.
The more resilient L2 will fulfill the
needs of 10Gb Ethernet networks with virtualized ecosystem and data migration. TRILL will also enable multi- hop capabilities for FCoE that will drive expanded adoption of FCoE in converged network environments.
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The result was a protocol called TRILL. Although routing is ordinarily done at Layer 3 of the ISO protocol stack, by making Layer 2 a routing layer, protocols other than IP, such as FCoE, can take advantage of this increased functionality. Multi-hopping allows specifying multiple paths through the network. By working in an arbitrary topology, links that otherwise would have been blocked are usable for traffic. Finally, if the network can use an existing link-state protocol, solution providers can use protocols that have already been developed, hardened, and optimized. This reduces the amount of work that must be done to deploy TRILL.
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