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Configuration Guide - Ethernet Switching

S7700 and S9700 V200R011C10

This document describes the configuration of Ethernet services, including configuring link aggregation, VLANs, Voice VLAN, VLAN mapping, QinQ, GVRP, MAC table, STP/RSTP/MSTP, SEP, and so on.
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Basic Concepts of Link Aggregation

Basic Concepts of Link Aggregation

As shown in Figure 3-1, DeviceA and DeviceB are connected through three Ethernet physical links. The three Ethernet physical links are bundled into an Eth-Trunk link, and the bandwidth of the Eth-Trunk link is the sum of bandwidth of the three Ethernet physical links. The three Ethernet physical links back up 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) is a logical link bundled by multiple Ethernet links.

    Each LAG corresponds to a logical interface, that is, link aggregation interface or Eth-Trunk. The Eth-Trunk can be used as a common Ethernet interface. The only difference between the Eth-Trunk and common 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 interface that forwards data and inactive interface that does not forward data.

    The link connected to an active interface is the active link, whereas 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 trouble-free member links are bundled into an Eth-Trunk link and each link provides a bandwidth of 1 Gbit/s. 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 based on 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. After the aggregated link is formed, LACP is responsible for maintaining the link status. When the link aggregation condition is changed, LACP adjusts or removes the aggregated link.

    Whether LACP is required

    No

    Yes

    Data forwarding

    Generally, all links are active links. All active links participate in data forwarding. If one active link fails, traffic is load balanced among the remaining active links.

    Generally, some links are active links. All active links participate in data forwarding. If an active link fails, the system selects a link among inactive links as the active link. That is, the number of links participating in data forwarding remains unchanged.

    Whether inter-device link aggregation is supported

    No

    Yes

    Fault detection

    This mode can only detect member link disconnections, but cannot detect other faults such as link layer faults and incorrect link connections.

    This mode can detect member link disconnections and other faults such as link layer faults and incorrect link connections.

    NOTE:
  • Link aggregation modes supported by the device

    • 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 based on LACP. For details, see E-Trunk.
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Updated: 2019-10-18

Document ID: EDOC1000178310

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