TRILL (Transparent Interconnection of Lots of Links) is an

Internet Standard In computer network engineering, an Internet Standard is a normative specification of a technology or methodology applicable to the Internet. Internet Standards are created and published by the Internet Engineering Task Force (IETF). They allow ...

implemented by devices called

TRILL switch A routing bridge or RBridge, also known as a TRILL switch, is a network device that implements the TRILL protocol, as specified by the IETF and should not be confused with BRouters (Bridging Routers). RBridges are compatible with previous IEEE 802 ...

es. TRILL combines techniques from bridging and

routing Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...

, and is the application of

link-state routing Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the others being distance-vector routing protocols. Examples of link-state routing protocols include ...

to the

VLAN A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer (OSI layer 2).IEEE 802.1Q-2011, ''1.4 VLAN aims and benefits'' In this context, virtual, refers to a physi ...

-aware customer-bridging problem.

Routing bridge A routing bridge or RBridge, also known as a TRILL switch, is a network device that implements the TRILL protocol, as specified by the IETF and should not be confused with BRouters (Bridging Routers). RBridges are compatible with previous IEEE 802 ...

s (RBridges) are compatible with and can incrementally replace previous

IEEE 802.1 IEEE 802.1 is a working group of the IEEE 802 project of the IEEE Standards Association. It is concerned with: * 802 LAN/MAN architecture * internetworking among 802 LANs, MANs and wide area networks * 802 Link Security * 802 overall network manage ...

customer bridges. TRILL Switches are also compatible with

IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...

and

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

, routers and

end system In networking jargon, a computer, phone, or internet of things device connected to a computer network is sometimes referred to as an end system or end station, because it sits at the edge of the network. The end user directly interacts with a ...

s. They are invisible to current IP routers, and like conventional routers, RBridges terminate the

broadcast, unknown-unicast and multicast traffic Broadcast, unknown-unicast and multicast traffic (BUM traffic) is network traffic transmitted using one of three methods of sending data link layer network traffic to a destination of which the sender does not know the network address. This is a ...

DIX Ethernet In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload. ...

and the frames of IEEE 802.2 LLC including the bridge protocol data units of the

Spanning Tree Protocol The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them. Spanning tree also al ...

. TRILL is the successor to Spanning Tree Protocol, both having been created by the same person,

Radia Perlman Radia Joy Perlman (; born December 18, 1951) is an American computer programmer and network engineer. She is a major figure in assembling the networks and technology to enable what we now know as the internet. She is most famous for her inventi ...

. The catalyst for TRILL was an event at

Beth Israel Deaconess Medical Center Beth Israel Deaconess Medical Center (BIDMC) in Boston, Massachusetts is a teaching hospital of Harvard Medical School. It was formed out of the 1996 merger of Beth Israel Hospital (founded in 1916) and New England Deaconess Hospital (founded ...

which began on 13 November 2002. The concept of Rbridges icwas first proposed to the

Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...

in 2004, who in 2005 rejected what came to be known as TRILL, and in 2006 through 2012 devised an incompatible variation known as Shortest Path Bridging.

General overview

TRILL switches run a

link-state routing protocol Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the others being distance-vector routing protocols. Examples of link-state routing protocols includ ...

amongst themselves. A link-state protocol is one in which connectivity is broadcast to all the RBridges, so that each RBridge knows about all the other RBridges, and the connectivity between them. This gives RBridges enough information to compute pair-wise optimal paths for

unicast Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication. In computer networking, unicast is a one-to-one transmission from one point in ...

, and calculate

distribution tree Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...

s for delivery of

frame A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...

s either to destinations whose location is unknown or to

multicast In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with ...

broadcast Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting began ...

groups. The link-state routing protocol used is

IS-IS Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this b ...

because: * it runs directly over

layer 2 The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer pr ...

, so it can be run without configuration o IP addresses need be assigned as it is inclusive of a subset of the Connectionless-mode Network Service (CLNP). * it is easy to extend by defining new

type–length–value Within communication protocols, TLV (type-length-value or tag-length-value) is an encoding scheme used for optional informational elements in a certain protocol. A TLV-encoded data stream contains code related to the record type, the record valu ...

(TLV) data elements and sub-elements for carrying TRILL information. To mitigate temporary loop issues, RBridges forward based on a header with a

hop count In wired computer networking, including the Internet, a hop occurs when a packet is passed from one network segment to the next. Data packets pass through Router (computing), routers as they travel between source and destination. The hop count ...

. RBridges also specify the next-hop RBridge as the frame destination when forwarding unicast frames across a shared-media link, which avoids spawning additional copies of frames during a temporary loop. A

reverse-path forwarding Reverse-path forwarding (RPF) is a technique used in modern routers for the purposes of ensuring loop-free forwarding of multicast packets in multicast routing and to help prevent IP address spoofing in unicast routing. In standard unicast IP r ...

check and other checks are performed on multi-destination frames to further control potentially looping traffic. The first RBridge that a unicast frame encounters in a campus, RB1, encapsulates the received frame with a TRILL header that specifies the last RBridge, RB2, where the frame is decapsulated. RB1 is known as the "ingress RBridge" and RB2 is known as the "egress RBridge". To save room in the TRILL header and simplify forwarding lookups, a dynamic nickname acquisition protocol is run among the RBridges to select two-

octet Octet may refer to: Music * Octet (music), ensemble consisting of eight instruments or voices, or composition written for such an ensemble ** String octet, a piece of music written for eight string instruments *** Octet (Mendelssohn), 1825 compos ...

nicknames for RBridges, unique within the campus, which are an abbreviation for the six-octet IS-IS system ID of the RBridge. The two-octet nicknames are used to specify the ingress and egress RBridges in the TRILL header. The TRILL header consists of six octets: the first two octets include a six-bit decrementing hop count, plus flags; the next two octets contain the egress RBridge nickname; the final two octets contain the ingress RBridge nickname. For multi-destination frames, the "egress RBridge nickname" specifies a distribution tree for the frame, where the (nick)named RBridge is the root of the distribution tree. The ingress RBridge selects which distribution tree the frame should travel along. Even though RBridges are transparent to

Layer 3 In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of transfe ...

devices, and all the links interconnected by RBridges appear to Layer 3 devices to be a single link, RBridges act as link routers in the sense that, in the forwarding of a frame by a transit RBridge, the outer Layer 2 header is replaced at each hop with an appropriate Layer 2 header for the next hop, and the hop count is decreased. Despite these modifications of the outer Layer 2 header and the hop count in the TRILL Header, the original encapsulated frame is preserved, including the original frame's VLAN tag. Multipathing of multi-destination frames through alternative distribution tree roots and

equal-cost multi-path routing Equal-cost multi-path routing (ECMP) is a routing strategy where packet forwarding to a single destination can occur over multiple best paths with equal routing priority. Multi-path routing can be used in conjunction with most routing protocols b ...

(ECMP) of unicast frames are supported. Networks with a more mesh-like structure benefit to a greater extent from the multipathing and optimal paths provided by TRILL than networks with a more tree-like structure. A host with multiple interfaces running the Internet Protocol requires that each of the interfaces r the group of interfaces in a teamhave a unique address, whereas when using TRILL the multiple-interface host can have a single IP address for all of its interfaces attached to a common broadcast domain — akin to the case of a network service access point address (NSAP) on an end system in CLNP.

TRILL links

From the point of view of TRILL, a link can be any of a wide variety of link technologies, including IEEE 802.3 (

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

), PPP (Point to Point Protocol)., or a

Pseudo-wire In computer networking and telecommunications, a pseudowire (or pseudo-wire) is an emulation of a point-to-point connection over a packet-switched network (PSN). The pseudowire emulates the operation of a "transparent wire" carrying the servic ...

. Ethernet links between RBridges can incorporate IEEE customer or provider 802.1 bridges. In other words, an arbitrary bridged LAN appears to an RBridge as a multi-access link. It is essential that only one RBridge act as the ingress RBridge for any given native frame and TRILL has an Appointed Forwarder mechanism to assure this. TRILL does allow load splitting of this duty on a link based on VLAN, so that only one RBridge on each link encapsulates and decapsulates native frames for each VLAN.

RBridge ports

RBridge ports can compatibly implement a wide variety of existing and proposed link level and IEEE 802.1 port level protocols including PAUSE (IEEE 802.3 Annex 31B), the

Link Layer Discovery Protocol The Link Layer Discovery Protocol (LLDP) is a vendor-neutral link layer protocol used by network devices for advertising their identity, capabilities, and neighbors on a local area network based on IEEE 802 technology, principally wired Ethern ...

(IEEE 802.1AB),

link aggregation In computer networking, link aggregation is the combining ( aggregating) of multiple network connections in parallel by any of several methods, in order to increase throughput beyond what a single connection could sustain, to provide redundan ...

(IEEE 802.1AX), MAC security (IEEE 802.1AE), or port based access control (IEEE 802.1X). This is because RBridges are layered above the IEEE 802.1 EISS (Extended Internal Sublayer Service) with the exception that an RBridge port handles spanning tree and VLAN registration PDUs differently.

Open source implementations

Accton IgniteNetbr>MeshLinq
— based on

Quagga The quagga ( or ) (''Equus quagga quagga'') is a subspecies of the plains zebra that was endemic to South Africa until it was hunted to extinction in the late 19th century. It was long thought to be a distinct species, but early genetic ...

0.99.22.4
Gandi'
quagga
with TRILL — based on

0.99.22.4
MichaelQQ'
Quagga-PE
featuring TRILL and MPLS — based on

0.99.22.4

Proprietary implementations

Cisco FabricPath is a proprietary implementation of TRILL that utilizes the TRILL control plane (including IS-IS for Layer 2), but a non-interoperable data plane. Brocade

Virtual Cluster Switching Virtual Cluster Switching (VCS) fabric technology is a Layer 2 proprietary Ethernet technology from Brocade Communications Systems, later acquired by Extreme Networks. It is designed to improve network utilization, maximize application availabilit ...

, uses the TRILL data plane but a proprietary control plane and so is not interoperable with standards conformant TRILL.

VLAN support

The TRILL protocol provides mandatory support for the usual 4K VLANs and can optionally support 24-bit Fine Grain Labels (FGL) in addition to VLANs. (RFC 7172 "TRILL: Fine Grained Labeling")

Competitors

The

IEEE 802.1aq Shortest Path Bridging (SPB), specified in the IEEE 802.1aq standard, is a computer networking technology intended to simplify the creation and configuration of Ethernet networks while enabling multipath routing. It is the replacement for the ...

standard (Shortest Path Bridging – SPB) is considered the major competitor of TRILL. As one 2011 book noted, "the evaluation of relative merits and difference of the two standards proposals is currently a hotly debated topic in the networking industry."

Product support

* Shanghai Baud Data Communication S5800 and S9500 *

Extreme Networks Extreme Networks is an American networking company based in San Jose, California. Extreme Networks designs, develops, and manufactures wired and wireless network infrastructure equipment and develops the software for network management, policy, a ...

BD-X series, Summit X670 series and Summit X770 series * HPE FlexFabric 5700, 9540 and 12900E *

Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops, produces and sells telecommunications equipment, consumer electronics and various smar ...

CloudEngine 5800, 6860, 8800 and 12800 * IgniteNet MeshLinq ML-S-4GE-1MGE * New H3C Technologies S6800, S6860, S10500 and S10500X * Ruijie Networks RG-S6220, RG-S12000 and RG-N18000 * Shenzhen Youhua Technology YH-S5800 and YH-S9500 *

ZTE Corporation ZTE Corporation is a Chinese partially state-owned technology company that specializes in telecommunication. Founded in 1985, ZTE is listed on both the Hong Kong and Shenzhen Stock Exchanges. ZTE's core business is wireless, exchange, opt ...

ZXR10 5960 and ZXR10 9900(-S)

References

External links

TRILL Working Group Charter
* "Routing Bridges (RBridges): Base Protocol Specification" * "PPP Transparent Interconnection of Lots of Links (TRILL) Protocol Control Protocol " (TRILL over PPP) * "Routing Bridges (RBridges): Appointed Forwarders" * "Fibre Channel over Ethernet (FCoE) over Transparent Interconnection of Lots of Links (TRILL)" * "Definitions of Managed Objects for Routing Bridges (RBridges)" * "TRILL: Fine Grained Labeling" * "TRILL: Transport Using Pseudowires" * "TRILL: Support of BFD" * "TRILL Use of IS-IS" * "TRILL: Adjacency"

by

and Donald Eastlake
Original RBridge paper, “Rbridges: Transparent Routing”
* {{IETF RFC, 5556, link=no, "Transparent Interconnection of Lots of Links (TRILL): Problem and Applicability Statement"
The Great Debate: TRILL Versus 802.1aq (SBP)
NANOG 50 session (October 2010)
Dissecting Cisco's FabricPath Ethernet technology
Link protocols