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 S2720, S5700, and S6700 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.

• 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 S2720, S5700, and S6700 V200R019C10 Configuration Guide - Ethernet Switching.

• 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 IP addresses are 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 S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support Ethernet sub-interfaces.

  • Only hybrid and trunk interfaces on the preceding switches support Ethernet 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 Ethernet 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 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.

• 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 S2720, S5700, and S6700 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 S2720, S5700, and S6700 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. A VE sub-interface can be created to allow an L2VPN to access to an L3VPN.