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Configuration Guide - Ethernet Switching

S7700 and S9700 V200R012C00

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, HVRP, and Layer 2 protocol transparent transmission.
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Basic Concepts of Link Aggregation

Basic Concepts of Link Aggregation

In Figure 3-1, DeviceA and DeviceB are connected through three physical Ethernet links. These links bundle into a logical link, and their bandwidths are combined to form the total bandwidth of the logical link. The three physical Ethernet links provide backup for each other, improving reliability.

Figure 3-1  Eth-Trunk networking

Link aggregation concepts are described as follows:

  • LAG and LAG interface

    A link aggregation group (LAG) binds multiple Ethernet links.

    Each LAG has one logical interface, that is, link aggregation interface or Eth-Trunk. The Eth-Trunk can be treated as a physical Ethernet interface. The only difference between the Eth-Trunk and physical Ethernet interface is that the Eth-Trunk needs to select one or more member interfaces to forward traffic.

  • Member interface and member link

    The interfaces that constitute an Eth-Trunk are member interfaces. The link corresponding to a member interface is a member link.

  • Active and inactive interfaces and links

    There are two types of interfaces in an LAG: active interfaces that forward data and inactive interfaces that do not forward data.

    The link connected to an active interface is the active link, and the link connected to an inactive interface is the inactive link.

  • Upper threshold for the number of active interfaces

    When the number of active interfaces reaches this threshold, the bandwidth of an Eth-Trunk will not increase even if more member links go Up. This guarantees higher network reliability. When the number of active member interfaces reaches the upper threshold, additional active member interfaces are set to Down.

    For example, 8 fully-functioning member links bundle into an Eth-Trunk link, with each link providing a bandwidth of 1 Gbit/s. If the Eth-Trunk link only needs to provide a maximum bandwidth of 5 Gbit/s, you can set the maximum number of Up member links to 5 or larger. Then any unselected Up links automatically enter the backup state, improving reliability.

    NOTE:

    The upper threshold for the number of active interfaces is inapplicable to the manual load balancing mode.

  • Lower threshold for the number of active interfaces

    When the number of active interfaces falls below this threshold, an Eth-Trunk goes Down. This guarantees the Eth-Trunk a minimum available bandwidth.

    For example, if the Eth-Trunk is required to provide a minimum bandwidth of 2 Gbit/s and each member link's bandwidth is 1 Gbit/s, the minimum number of Up member links must be set to 2 or larger.

  • Link aggregation mode

    There are two link aggregation modes: manual and LACP. Table 3-1 compares the two modes.

    Table 3-1  Comparisons between link aggregation modes

    Item

    Manual Mode

    LACP Mode

    Definition

    You must manually create an Eth-Trunk and add member interfaces to the Eth-Trunk. In this mode, LACP is not required.

    An Eth-Trunk is created using LACP. LACP provides a standard negotiation mechanism for a switching device so that the switching device can automatically form and start the aggregated link according to its configuration. LACP is responsible for maintaining the link status after the aggregated link is formed and adjusting or removing the aggregated link when the link aggregation condition is changed.

    LACP

    Not required

    Required

    Data forwarding

    When the aggregated link is operating normally, all links are active links and participate in data forwarding. If one active link fails, traffic is load balanced among the remaining active links.

    When the aggregated link is operating normally, only some links are active links. All active links participate in data forwarding. If an active link fails, the system selects one of the inactive links to be the active link, ensuring the number of links participating in data forwarding remains unchanged.

    Inter-device link aggregation

    Not supported

    Supported

    Fault detection

    This mode can only detect member link disconnections.

    This mode can detect member link disconnections, link layer faults, and incorrect link connections.

    NOTE:
  • Link aggregation is supported in the following cases:

    • Intra-card: Member interfaces of an Eth-Trunk are located on the same card.
    • Inter-card: Member interfaces of an Eth-Trunk are located on different cards.
    • Inter-chassis: Member interfaces of an Eth-Trunk are located on member devices of a CSS. For details, see Link Aggregation in CSS Scenarios.
    • Inter-device: The inter-device link aggregation refers to E-Trunk. E-Trunk allows links between multiple devices to be aggregated using LACP. For details, see E-Trunk.
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Updated: 2019-01-18

Document ID: EDOC1100038843

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