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S12700 V200R010C00 Configuration Guide - Ethernet Switching

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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E-Trunk

E-Trunk

Enhanced Trunk (E-Trunk) is an extension of LACP. It controls and implements link aggregation among multiple devices. E-Trunk implements device-level link reliability, instead of the card-level link reliability implemented by LACP.

E-Trunk is mainly applied to a scenario where a CE is dual-homed to a VPLS, VLL, or PWE3 network. Without E-Trunk, a CE can connect to only one PE by using an Eth-Trunk link. If the Eth-Trunk or PE fails, the CE cannot communicate with the PE. By using E-Trunk, the CE can be dual-homed to PEs to protect PEs and links between the CE and PEs, enabling device-level protection.

Figure 3-12  E-Trunk networking

Basic Concepts

  • LACP system priority

    LACP system priorities are used to differentiate priorities of devices at both ends of an Eth-Trunk link. A smaller value indicates a higher LACP system priority.

  • System ID

    In LACP, the system ID is used to determine the priorities of the two devices at both ends of an Eth-Trunk link if their LACP priorities are the same. A smaller system ID indicates a higher priority. By default, the system ID is the MAC address of an Eth-Trunk.

    To enable a CE to consider the PEs as a single device, you must configure the same system LACP priority and system ID for the PEs at both ends of an E-Trunk link.

  • E-Trunk priority

    The E-Trunk priority determines the master/backup status of two devices in an LAG. A device with a higher E-Trunk priority becomes the master device, and the other one becomes the backup device. A smaller E-Trunk priority value indicates a higher E-Trunk priority.

  • E-Trunk ID

    An E-Trunk ID is an integer that identifies an E-Trunk.

  • Working mode

    The working mode depends on the working mode of the Eth-Trunk added to the E-Trunk. The Eth-Trunk can work in one of the following modes:

    • Automatic

    • Forced master

    • Forced backup

  • Timeout interval

    The master and backup devices in an E-Trunk periodically send hello packets to each other. If the backup device does not receive any hello packets within the timeout interval, it becomes the master device.

E-Trunk Working Principle

The E-Trunk working process is as follows:

  • Master/Backup status negotiation

    Using Figure 3-12 as an example, the CE is directly connected to PE1 and PE2, and E-Trunk1 runs between PE1 and PE2.

    • PE

      The same Eth-Trunk and E-Trunk are created on PE1 and PE2. In addition, the Eth-Trunks are added to the E-Trunk.

    • CE

      An Eth-Trunk in LACP mode is configured on the CE. The CE is connected to PE1 and PE2 through the Eth-Trunk.

      The E-Trunk is invisible to the CE.

    1. Determine the E-Trunk master/backup status.

      PE1 and PE2 negotiate the E-Trunk master/backup status by exchanging E-Trunk packets. After the negotiation, one PE functions as the master and the other as the backup.

      The master/backup status of a PE depends on the E-Trunk priority and E-Trunk ID carried in E-Trunk packets. The PE with the higher E-Trunk priority functions as the master device. If the E-Trunk priorities of the PEs are the same, the PE with the smaller E-Trunk system ID functions as the master device.

    2. Determine the master/backup status of a member Eth-Trunk in the E-Trunk.

      The master/backup status of a member Eth-Trunk in the E-Trunk is determined by its E-Trunk status and the remote Eth-Trunk status.

      In Figure 3-12, PE1 and PE2 are at both ends of the E-Trunk link. In this example, PE1 is considered the local device and PE2 is the remote device.

      Figure 3-12 describes the status of each member Eth-Trunk in the E-Trunk.

      Table 3-2  Master/Backup status of an E-Trunk and its member Eth-Trunks

      Local E-Trunk Status

      Working Mode of the Local Eth-Trunk

      Remote Eth-Trunk Status

      Local Eth-Trunk Status

      -

      Forced master

      -

      Master

      -

      Forced backup

      -

      Backup

      Master

      Automatic

      Down

      Master

      Backup

      Automatic

      Down

      Master

      Backup

      Automatic

      Up

      Backup

      In normal situations:

      • PE1 functions as the master and Eth-Trunk 10 of PE1 enters the master state with a link status of Up.

      • PE2 functions as the backup and Eth-Trunk 10 of PE2 enters the backup state with a link status of Down.

      If the link between the CE and PE1 fails, the following occurs:

      1. PE1 sends an E-Trunk packet containing information about faulty Eth-Trunk 10 of PE1 to PE2.

      2. After receiving the E-Trunk packet, PE2 finds that Eth-Trunk 10 on PE1 is faulty. Eth-Trunk 10 on PE2 becomes the master. Through LACP negotiation, Eth-Trunk 10 on PE2 becomes Up.

        The Eth-Trunk status on PE2 becomes Up, and traffic from the CE is forwarded through PE2, preventing traffic interruption.

      If PE1 fails, the following occurs:

      1. If the PEs are configured with BFD, PE2 detects that the BFD session status becomes Down and then switches to be the master, and Eth-Trunk 10 on PE2 enters the master state.

      2. If the PEs are not configured with BFD, PE2 will not receive any E-Trunk packets from PE1 before the timeout, causing PE2 to take over as the master. Eth-Trunk 10 on PE2 will also function as the master.

        Through LACP negotiation, Eth-Trunk 10 on PE2 becomes Up. The traffic of the CE is forwarded through PE2. This protects traffic destined for the remote CE.

  • Sending and receiving of E-Trunk packets

    E-Trunk packets carrying the source IP address and port number configured on the local device are sent through UDP. E-Trunk packets are sent in the following situations:
    • The packet sending timer times out.

    • The configurations change. For example, the E-Trunk priority, packet sending interval, timeout interval multiplier, or the source/destination IP address of the E-Trunk changes, or member Eth-Trunks are added or deleted.

    • A member Eth-Trunk fails or recovers.

    E-Trunk packets need to carry their timeout interval. The remote device uses this interval as the timeout interval of the local device.

  • BFD

    BFD enables a device to quickly detect a fault on the remote device based on the timeout interval of received packets. The IP address of the remote device needs to be specified on the local device, and a BFD session needs to be established to detect the reachability of the route to the remote device. Then the E-Trunk can detect any fault detected by BFD.

  • Switchback mechanism

    If the Eth-Trunk on the local device in master state goes Down or the local device fails, the remote device becomes the master and the member Eth-Trunk becomes Up.

    When the local device recovers, the local Eth-Trunk enters the LACP negotiation state. After LACP informs the local E-Trunk that the negotiation capability is Up, the local device starts the switchback delay timer. After the switchback delay timer expires, the local Eth-Trunk becomes the master and goes Up after LACP negotiation.

E-Trunk Constraints

Using Figure 3-12 as an example, to improve reliability links between the CE and PEs and guarantee that traffic is properly switched between these links, pay attention to the following points:

  • The configurations at both ends of the E-Trunk link must be consistent. The Eth-Trunks linked directly to the PEs and the CE must be configured with the same working rate and duplex mode so that both Eth-Trunks have the same key and join the same E-Trunk. After the Eth-Trunks are added to the E-Trunk, both PEs must contain the LACP system priorities and IDs. The interfaces connecting the CE to PE1 and PE2 must be added to the same Eth-Trunk. The Eth-Trunk on the CE can have a different ID from that of the PEs. For example, the CE is configured with Eth-Trunk 1, and both PEs are configured with Eth-Trunk 10.

  • To ensure Layer 3 connectivity, the IP address of the local PE must be the same as the local address of the remote PE and the IP address of the remote PE must be the same as the remote address of the local PE. Therefore, it is recommended that the addresses of the PEs are configured as loopback interface addresses.

  • The E-Trunk must be bound to a BFD session.

  • The two PEs must be configured with the same security key.

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Updated: 2019-08-21

Document ID: EDOC1000142081

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