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S12700 V200R012C00 Configuration Guide - Ethernet Switching

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, and Layer 2 protocol transparent transmission.

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Link and Interface Types

Link and Interface Types

All frames processed in a switch carry VLAN tags. On a network, some devices connected to a switch can only receive and send untagged frames. To enable communication between the switch and these devices, the switch interfaces must be able to identify the untagged frames and add or remove VLAN tags when receiving or sending frames. Hosts in the same VLAN may be connected to different switches, and more than one VLAN may span multiple switches. To enable communication between hosts, interfaces connecting switches must be able to identify and send frames from multiple VLANs.

To accommodate different connections and networking, Huawei defines four interface types (access, trunk, hybrid, and QinQ) and two link types (access and trunk). Figure 4-3 shows access, trunk, and hybrid interfaces. QinQ Configuration shows the QinQ interface.

Figure 4-3  Link and interface types

Link Types

As shown in Figure 4-3, the following are the two types of Ethernet links, which differ in the number of VLANs they can transmit frames from:

  • Access link

    An access link can transmit data frames of only one VLAN. It connects a switch to a user terminal, such as a host, server, or simplified Layer 2 switch. Generally, user terminals do not need to know the VLANs to which they belong and cannot identify tagged frames; therefore, only untagged frames are transmitted along an access link.

  • Trunk link

    A trunk link can transmit data frames of multiple VLANs. It connects a switch to another switch or a router. Frames on a trunk link must be tagged so that other network devices can correctly identify VLAN information in the frames.

Interface Types

As shown in Figure 4-3, the following are the different types of Ethernet interfaces, which differ in the objects connected to them and the way they process frames:

  • Access interface

    An access interface often connects to a user terminal such as a user host or server that cannot identify VLAN tags, or is used when VLANs do not need to be differentiated. In most cases, access interfaces can only receive and send untagged frames, and can add only a unique VLAN tag to untagged frames. However, if the VID and PVID are the same in tagged frames, access interfaces can receive and process the tagged frames.

  • Trunk interface

    A trunk interface often connects to a switch, router, AP, or voice terminal that can receive and send tagged and untagged frames simultaneously. It allows tagged frames from multiple VLANs and untagged frames from only one VLAN.

  • Hybrid interface

    A hybrid interface can connect to not only a user terminal (such as a user host or server) or network device (such as a hub or simplified Layer 2 switch) that cannot identify tags, but also a switch, router, voice terminal, or AP that can receive and send tagged and untagged frames. It allows tagged frames from multiple VLANs. Frames sent out from a hybrid interface are tagged or untagged according to the VLAN configuration.

    Hybrid interfaces can be used in the same scenarios as trunk interfaces. However, there are some scenarios, such as the selective QinQ scenario, in which only a hybrid interface can be used. Before packets from multiple VLANs provided by a service provider enter a user network, the outer VLAN tags must be removed. The trunk interface cannot be used here because the trunk interface allows only untagged packets from its default VLAN to pass through. For details about selective QinQ, see Configuring Selective QinQ in "QinQ Configuration".

  • QinQ interface

    An 802.1Q-in-802.1Q (QinQ) interface often connects a private network to a public network. It can add an additional 802.1Q tag to a tagged frame. QinQ supports up to 4094 x 4094 VLANs, thereby extending VLANs over the network. The outer tag is often called the public tag and identifies the VLAN ID of the public network, whereas the inner tag is often called the private tag and identifies the VLAN ID of the private network.

    For details about the QinQ interface and QinQ frame format, see QinQ Fundamentals.

Updated: 2019-01-18

Document ID: EDOC1100038103

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