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Configuration Guide - Interface Management

S1720, S2700, S5700, and S6720 V200R010C00

This document describes the principles and configurations of interfaces and provides configuration examples.

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Logical Interface Overview

Logical Interface Overview

This section describes logical interfaces supported by switches.

  • Eth-Trunk

    An Eth-Trunk has Layer 2 and Layer 3 features and is formed by binding multiple Ethernet interfaces to provide more bandwidth and higher transmission reliability. For details about how to configure an Eth-Trunk, see Link Aggregation Configuration in the S1720, S2700, S5700, and S6720 V200R010C00 Configuration Guide - Ethernet Switching.

  • Tunnel interface

    A tunnel interface has Layer 3 features, transmits packets, and identifies and processes packets transmitted over a tunnel.

  • VLANIF interface

    A VLANIF interface has Layer 3 features, and enables VLANs to communicate and can have Layer 3 services deployed after being assigned an IP address. For details about how to configure a VLANIF interface, see Configuration Examples in "VLAN Configuration" in the S1720, S2700, S5700, and S6720 V200R010C00 Configuration Guide - Ethernet Switching.

  • Sub-interface

    Sub-interfaces are multiple logical interfaces configured on a main interface to allow the main interface to communicate with multiple remote interfaces. Sub-interfaces can share physical layer parameters of their main interface, or be configured with their respective link layer parameters and network layer parameters. Disabling or activating sub-interfaces does not affect the main interface status, but the main interface status change affects the status of sub-interfaces. Sub-interfaces work properly only when their main interface is in Up state. Associating a sub-interface with a VLAN implements inter-VLAN communication and applies to Dot1q termination and QinQ termination scenarios. For configuration details, see VLAN Termination Configuration in the S1720, S2700, S5700, and S6720 V200R010C00 Configuration Guide - Ethernet Switching.

    The switch supports sub-interface configuration on Ethernet interfaces and Eth-Trunks.

    Sub-interfaces are classified into Layer 2 sub-interfaces and Layer 3 sub-interfaces based on whether IP addresses are configured.

    • Layer 2 sub-interfaces: have no IP address configured, work at the data link layer, and are used for across-tunnel packet forwarding in the same VLAN on the same network segment, for example, in L2VPN scenarios.
    • Layer 3 sub-interfaces: have IP addresses configured, work at the network layer, and are used for packet forwarding between different network segments, for example, in L3VPN scenarios.
    • Only the S6720EI, S6720S-EI, S5720HI and S5720EI support sub-interfaces.

    • Only hybrid and trunk interfaces on the preceding switches support sub-interface configuration.
    • After you run the undo portswitch command to switch Layer 2 interfaces on the preceding series of switches into Layer 3 interfaces, you can configure sub-interfaces on the interfaces.

    • After an interface is added to an Eth-Trunk, sub-interfaces cannot be configured on the interface.

    • VLAN termination sub-interfaces cannot be created on a VCMP client.
  • Loopback interface

    According to TCP/IP, an interface with an IP address in the range of to is a loopback interface. A loopback interface can be either of the following:

    • Loopback interface

      A loopback interface is used when you need an interface that must be always in the Up state. A loopback interface has the following advantages:

      • Once a loopback interface is created, its physical status and data link protocol status always stay Up, regardless of whether an IP address is configured for the loopback interface.

      • A loopback interface can be assigned an IP address with a 32-bit mask, which reduces address consumption. The IP address of a loopback interface can be advertised immediately after being configured.

      • No link layer protocol can be configured for a loopback interface. Therefore, no data link layer negotiation is required, allowing the link layer protocol status of the interface to stay Up.

      • The device drops the packet with a non-local IP address as the destination IP address and a local loopback interface as the outbound interface.

      The advantages of a loopback interface help improve configuration reliability. The IP address of a loopback interface can be used as follows:
      • Can be configured as a packet's source IP address to improve network reliability.
      • Can be used to control an access interface and filter logs to simplify information displaying.
    • InLoopback0 interface

      An InLoopBack0 interface is a fixed loopback interface that is automatically created at the system startup.

      An InLoopBack0 interface uses the fixed loopback address to receive data packets destined for the host where the InLoopBack0 interface resides. The loopback address of an InLoopBack0 interface is not advertised.

  • NULL interface

    A null interface is used to filter routes because any data packets received by the null interface are discarded.

Updated: 2019-12-28

Document ID: EDOC1000141936

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