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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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Introduction to VLAN Switch

Introduction to VLAN Switch

VLAN Switch is a forwarding method that forwards data according to the information in VLAN tags of received frames. This method requires a pre-configured static forwarding path along switching nodes on the network. When receiving VLAN-tagged frames matching VLAN Switch entries, a switching node forwards the frames to the interfaces manually specified in the VLAN Switch table. VLAN Switch improves device forwarding efficiency and security, and prevents MAC address attacks as well as broadcast storms.

VLAN Switch includes two sub-functions: switch-vlan and stack-vlan.

  • Stack-vlan: adds an outer VLAN tag to packets.

  • Switch-vlan: changes outer VLAN tags when forwarding packets between different interfaces.

Stack-vlan

Similar to the VLAN stacking function, the stack-vlan function is a Layer 2 feature that adds an outer VLAN tag to each frame, and decides which outer VLAN tags to be added to frames depending on information in the original VLAN tags carried in the frames. Table 6-1 lists the comparison between VLAN stacking and stack-vlan. For details about VLAN stacking, see Selective QinQ.

Table 6-1  Comparison between stack-vlan and VLAN stacking

Function

Similarities

Differences

Advantages and Disadvantages

Stack-vlan

  • A receiving interface adds a new VLAN tag outside the original VLAN tag of a received frame.

  • An interface processes frames as follows:

    • Adds different VLAN tags to the frames sent from different VLANs.

    • Adds VLAN tags when receiving frames; removes the outer-most VLAN tags when sending frames out of the interface.

VLAN Switch requires a pre-configured static forwarding path along switching nodes on the network. When receiving VLAN-tagged frames matching VLAN Switch entries, a switching node forwards the frames to the interfaces manually specified in the VLAN Switch table.

The VLANs used in VLAN Switch cannot be created in the system view.

  • Advantage:

    Switching nodes forward frames without searching for the MAC address table, which improves forwarding efficiency and network security, and prevents MAC address attacks as well as broadcast storms.

  • Disadvantage:

    If a large number of user devices connect to a switching node, the network administrator needs to configure a VLAN Switch entry for each user device on the switching node to establish a static forwarding path. This increases the network administrator's workload and complicates network management.

VLAN stacking

Frames are forwarded after looking up the entries in the MAC address table.

  • Advantage:

    The administrator does not need to specify a static forwarding path, thereby simplifying user access. Frames are forwarded according to the information in the MAC address table.

  • Disadvantage:

    Device forwarding efficiency is low, and the network is prone to broadcast storms and MAC address attacks.

Switch-vlan

Similar to the VLAN mapping function, the switch-vlan function implements inter-VLAN communication. Table 6-2 lists the comparison between VLAN mapping and switch-vlan. For details about VLAN mapping, see Principles.

Table 6-2  Comparison between switch-vlan and VLAN mapping

Function

Similarities

Differences

Advantages and Disadvantages

Switch-vlan

  • After receiving a VLAN-tagged frame, an interface replaces the outer VLAN tag of the frame.

  • Before sending a frame to another VLAN, an interface configured with VLAN mapping or switch-vlan replaces the VLAN tag of the frame with the destination VLAN tag.

  • After receiving a frame from another VLAN, an interface replaces the VLAN tag of the frame with the local VLAN tag.

VLAN Switch requires a pre-configured static forwarding path along switching nodes on the network. When receiving VLAN-tagged frames matching VLAN Switch entries, a switching node forwards the frames to the interfaces manually specified in the VLAN Switch table.

The VLANs used in VLAN Switch cannot be created in the system view.

  • Advantage:

    Switching nodes forward frames without searching for the MAC address table, which improves forwarding efficiency and network security, and prevents MAC address attacks as well as broadcast storms.

  • Disadvantage:

    If a large number of user devices connect to a switching node, the network administrator needs to configure a VLAN Switch entry for each user device on the switching node to establish a static forwarding path. This increases the network administrator's workload and complicates network management.

VLAN mapping

A switch configured with VLAN mapping forwards frames according to the MAC address table.

VLAN mapping requires that IP addresses of devices in both VLANs be on the same network segment.

  • Advantage:

    The administrator does not need to specify a static forwarding path, thereby simplifying user access. Frames are forwarded according to the information in the MAC address table.

  • Disadvantage:

    Device forwarding efficiency is low, and the network is prone to broadcast storms and MAC address attacks.

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Updated: 2019-08-21

Document ID: EDOC1000142081

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