Overview of Logical Interfaces

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 S7700 V200R019C10 Configuration Guide - Ethernet Switching.

• Tunnel interface

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

• MTunnel interface

  An MTunnel interface (MTI) is the ingress or egress of a multicast tunnel (MT). The local provider edge (PE) sends data of the private network through the MTI, and the remote PE receives data of the private network through the MTI. For details about how to configure a tunnel interface, see Configuring MTI Parameters in "Multicast VPN Configuration" in the S7700 V200R019C10 Configuration Guide - IP Multicast.

• 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 S7700 V200R019C10 Configuration Guide - Ethernet Switching.

• Logical CSS interface

  A logical CSS interface is a logical interface used to implement the CSS function. The CSS function virtualizes multiple switches into a logical switch to provide massive data forwarding and improve network reliability in data centers. For details about how to configure a CSS interface, see S7700 V200R019C10 Configuration Guide - Device Management.

• Ethernet sub-interface

  Ethernet sub-interfaces are multiple logical interfaces configured on a main interface to allow the main interface to communicate with multiple remote interfaces. Ethernet 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 Ethernet sub-interfaces does not affect the main interface status, but the main interface status change affects the status of Ethernet sub-interfaces. Ethernet sub-interfaces work properly only when their main interface is in Up state.

  Ethernet sub-interfaces are classified into Layer 2 Ethernet sub-interfaces and Layer 3 Ethernet sub-interfaces based on whether they can have IP addresses configured.

  • Layer 2 Ethernet 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 Ethernet 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 E series, X series, F series, and SC series cards support Ethernet sub-interface configuration. For details about the cards, see Cards in the Hardware Description.

  • Only hybrid and trunk interfaces on the preceding series of cards support Layer 2 Ethernet sub-interface configuration.

  • After you run the undo portswitch command to switch Layer 2 interfaces on the preceding series of cards into Layer 3 interfaces, you can configure Layer 3 Ethernet sub-interfaces on the interfaces.

  • The SA series cards do not support Ethernet sub-interface configuration and cannot forward IP traffic to Ethernet sub-interfaces on other cards.

  • You are advised to add a member interface to an Eth-Trunk and then configure an Eth-Trunk sub-interface. The Eth-Trunk sub-interface can be successfully configured only when the card on which the member interface locates supports Ethernet sub-interface configuration.

  • 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 127.0.0.0 to 127.255.255.255 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 127.0.0.1/8 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.

• Virtual-Template (VT) interface

  A VT interface is used when PPP needs to transmit packets of other link layer protocols. For example, a virtual template contains the negotiation parameters required for PPPoE authentication, including authentication methods, negotiation timeout interval, and maximum receive unit (MRU). For details about how to configure a VT interface, see Configuring a Virtual Template in "PPPoE Configuration" in the S7700 V200R019C10 Configuration Guide - User Access and Authentication.

• NVE interface

  An NVE interface is a logical interface used to establish a VXLAN tunnel with another NVE device. For details about how to configure an NVE interface, see S7700 V200R019C10 Configuration Guide - VXLAN Configuration.

• VBDIF interface

  A VBDIF interface is a virtual interface based on a bridge domain and supporting Layer 3 features. VBDIF interfaces implement communication between BDs, between BD and non-BD networks, and between BD and Layer 3 networks. For details about how to configure a VBDIF interface, see S7700 V200R019C10 Configuration Guide - VXLAN Configuration.

• VE interface

  A VE interface is used when other data link layer protocols need to be carried by the Ethernet protocol.