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    Ethernet Terms and Acronyms

    Networking with a switch over Ethernet on a LAN is different than networking with a router with IP over a wider area. Even the words used to talk about Ethernet networking are different from those used in IP routing. This topic provides a list of all the terms and acronyms used in the Junos OS Layer 2 Switching and Bridging Library , as well terms that apply to a complete network using Ethernet as a carrier technology.

    • 802.1ad—The IEEE specification for “Q-in-Q” encapsulation and bridging of Ethernet frames.
    • 802.1ah—The IEEE specification for media access control (MAC) tunneling encapsulation and bridging of Ethernet frames across a provided backbone-managed bridge.
    • 802.3ag—The IEEE specification for a wide range of Ethernet Operations, Administration, and Maintenance (OAM) features. See also OAM, CFM, and ETH-DM.
    • 802.3ah—The IEEE specification for link fault management (LFM), a method for OAM of Ethernet links.
    • 802.1Q—The IEEE specification for adding virtual local area network (VLAN) tags to an Ethernet frame.
    • B–MAC—The backbone source and destination MAC address fields found in the IEEE 802.1ah provider MAC encapsulation header.
    • bridge—A network component defined by the IEEE that forwards frames from one LAN segment or VLAN to another. The bridging function can be contained in a router, LAN switch, or other specialized device. See also switch.
    • bridge domain—A set of logical ports that share the same flooding or broadcast characteristics. As in a virtual LAN, a bridge domain spans one or more ports of multiple devices. By default, each bridge domain maintains its own forwarding database of MAC addresses learned from packets received on ports belonging to that bridge domain. See also broadcast domain and VLAN.
    • B-TAG—A field defined in the IEEE 802.1ah provider MAC encapsulation header that carries the backbone VLAN identifier information. The format of the B-TAG field is the same as that of the IEEE 802.1ad S-TAG field. See also S-TAG.
    • B-VID—The specific VLAN identifier carried in a B-TAG.
    • CFM—Connectivity-fault management. The part of Ethernet OAM that monitors events at levels above the physical level, as does LFM. See also OAM, LFM, and ETH-DM.
    • CIST—Common and Internal Spanning Tree. The single spanning tree calculated by the spanning tree protocol (STP) and the rapid spanning tree protocol (RSTP) and the logical continuation of that connectivity through multiple spanning tree (MST) bridges and regions, calculated to ensure that all LANs in the bridged LAN are simply and fully connected. See also MSTI.
    • ETH-DM—Ethernet Frame Delay Measurements. See also OAM, CFM, and Y.1731.
    • Ethernet—A term loosely applied to a family of LAN standards based on the original proprietary Ethernet from DEC, Intel, and Xerox (DIX Ethernet), and the open specifications developed by the IEEE 802.3 committee (IEEE 802.3 LANs). In practice, few LANs comply completely with DIX Ethernet or IEEE 802.3.
    • IRB—Integrated bridging and routing. IRB provides simultaneous support for Layer 2 bridging and Layer 3 routing within the same bridge domain. Packets arriving on an interface of the bridge domain are Layer 2 switched or Layer 3 routed based on the destination MAC address. Packets addressed to the router's MAC address are routed to other Layer 3 interfaces.
    • I-SID—The 24–bit service instance identifier field carried inside an I-TAG. The I-SID defines the service instance to which the frame is mapped.
    • I-TAG—A field defined in the IEEE 802.1ah provider MAC encapsulation header that carries the service instance information (I-SID) associated with the frame.
    • learning domain—A MAC address database where the MAC addresses are added based on the normalized VLAN tags.
    • LFM—Link fault management. A method used to detect problems on links and spans on an Ethernet network defined in IEEE 802.3ah. See also OAM.
    • MSTI—Multiple Spanning Tree Instance. One of a number of spanning trees calculated by MSTP within an MST region. The MSTI provides a simple and fully connected active topology for frames classified as belonging to a VLAN that is mapped to the MSTI by the MST configuration table used by the MST bridges of that MST region. See also CIST.
    • MSTP—Multiple Spanning Tree Protocol. A spanning-tree protocol used to prevent loops in bridge configurations. Unlike other types of STPs, MSTP can block ports selectively by VLAN. See also RSTP.
    • OAM—Operation, Administration, and Maintenance. A set of tools used to provide management for links, device, and networks. See also LFM.
    • PBB—Provider backbone bridge.
    • Q-in-Q—See 802.1ad.
    • PBBN—Provider backbone bridged network.
    • RSTP—Rapid Spanning Tree Protocol. A spanning-tree protocol used to prevent loops in bridge configurations. RSTP is not aware of VLANs and blocks ports at the physical level. See also MSTP.
    • S-TAG—A field defined in the IEEE 802.1ad Q-in-Q encapsulation header that carries the S-VLAN identifier information. See also B-TAG.
    • S-tagged service interface—The interface between a customer edge (CE) device and the I-BEB or IB-BEB network components. Frames passed through this interface contain an S-TAG field. See also B-tagged service interface.
    • S-VLAN—The specific service instance VLAN identifier carried inside the S-TAG field. See also B-VID.
    • switch—A network device that attempts to perform as much of the forwarding task in hardware as possible. The switch can function as a bridge (LAN switch), router, or some other specialized device, and forwards frames, packets, or other data units. See also bridge.
    • virtual switch—A routing instance that can contain one or more bridge domains.
    • VLAN—Virtual LAN. Defines a broadcast domain, a set of logical ports that share the same flooding or broadcast characteristics. VLANs span one or more ports on multiple devices. By default, each VLAN maintains its own Layer 2 forwarding database containing MAC addresses learned from packets received on ports belonging to the VLAN. See also bridge domain.
    • Y.1731—The international standard for Ethernet Frame Delay Measurements (ETH-DM).

    At this point, these acronyms and terms are just a bewildering array of letters and words. It is the goal of this manual to make the contents of this list familiar and allow you to place each of them in context and understand how they relate to each other. To do that, a basic understanding of modern Ethernet standards and technology is necessary.

    Modified: 2017-08-31