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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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E-Trunk

E-Trunk

Enhanced Trunk (E-Trunk) is an extension based on the Link Aggregation Control Protocol (LACP). E-Trunk controls and implements link aggregation among multiple devices, whereas LACP does so for just one device. While LACP can guarantee reliability when a card fails, E-Trunk does so even when a device fails.

E-Trunk is suitable to scenarios where a CE is dual-homed to a VPLS, VLL, or PWE3 network. In this scenario, E-Trunk can be used to protect PEs and links between the CE and PEs. Without E-Trunk, a CE can be connected 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, providing device-level protection.

Figure 3-12  E-Trunk networking

Basic Concepts

  • LACP system priority

    In LACP, the LACP system priority is 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. The smaller the system ID, the higher the 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 priorities determine the master/backup status of two devices in a LAG. On the network shown in Figure 3-12, if PE1 has a higher E-Trunk priority than PE2, PE1 is the master device and PE2 is the backup device. In priority comparisons, numerically lower values have higher 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 works in one of the following modes:

    • Automatic

    • Forcible master

    • Forcible backup

  • Timeout interval

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

E-Trunk Working Principles

The E-Trunk working principles are described as follows:

  • Master/Backup status negotiation

    As shown in Figure 3-12, the CE is directly connected to PE1 and PE2, and E-Trunk runs between PE1 and PE2.

    • PEs

      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. Normally, 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 smaller the E-Trunk priority value, the higher the E-Trunk priority. The PE with the higher E-Trunk priority functions as the master. 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.

      As shown in Figure 3-12, PE1 and PE2 are at both ends of the E-Trunk link. PE1 is considered as the local end and PE2 as the remote end.

      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

      -

      Forcible master

      -

      Master

      -

      Forcible backup

      -

      Backup

      Master

      Automatic

      Down

      Master

      Backup

      Automatic

      Down

      Master

      Backup

      Automatic

      Up

      Backup

      In normal situations:

      • If PE1 functions as the master, Eth-Trunk 10 of PE1 enters the master state and its link status is Up.

      • If PE2 functions as the backup, Eth-Trunk 10 on PE2 enters the backup state and its link status is 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 the remote device is faulty. Eth-Trunk 10 on PE2 becomes the master. Through LACP negotiation, Eth-Trunk 10 on PE2 becomes Up, and traffic of the CE is forwarded through PE2. This ensures that traffic destined for the CE is protected.

      If PE1 fails, the following situations occur:

      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 packet from PE1 before the timeout. PE2 and Eth-Trunk 10 on PE2 will enter the master state. Through LACP negotiation, Eth-Trunk 10 on PE2 becomes Up, and traffic of the CE is forwarded through PE2. This ensures that traffic destined for the remote CE is protected.

  • Sending and receiving of E-Trunk packets

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

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

    • A member Eth-Trunk fails or recovers.

    E-Trunk packets at the local end need to carry the timeout interval so that the remote device can use the timeout interval in Eth-Trunk packets from the local end as its timeout interval.

  • BFD

    A device cannot quickly detect a fault on its remote end based on the timeout interval of received packets. BFD can be configured on the device. The IP address of the remote end 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 physical status of 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 physical status of the member Eth-Trunk becomes Up.

    When the local device recovers and needs to function as the master, the local Eth-Trunk enters the LACP negotiation state. After LACP indicates 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 its status is Up.

E-Trunk Constraints

On the network shown in Figure 3-12, comply with the following constraints to improve reliability of CE and PE links and ensure that traffic is switched between these links:

  • The configurations at both ends of the E-Trunk link must be consistent. The Eth-Trunk links directly connecting PEs to 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 same LACP system priorities and IDs. The interfaces on the CE connecting 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.

  • 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 to ensure Layer 3 connectivity. 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, if necessary.

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Updated: 2019-01-18

Document ID: EDOC1100038843

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