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VPP Kernel Interfaces Configuration
VPP kernel interfaces provide a bridge between the high-performance VPP data plane and the Linux kernel networking stack. These interfaces appear as standard network interfaces in the kernel while being transparently connected to VPP interfaces, enabling seamless integration between VPP processing and kernel-based applications.
How Kernel Interfaces Work:
Traffic sent to the kernel interface by any application or kernel is forwarded to the connected VPP interface
Traffic processed within VPP is sent to the kernel interface only if VPP cannot handle it (e.g., no matching route)
Standard Linux networking tools and daemons can interact with VPP interfaces
Use Cases:
Integrating VPP interfaces with routing daemons (FRR, BIRD)
Providing management access to VPP-processed networks
Running standard network services on VPP interfaces
Interface Types: TUN vs TAP
VPP kernel interfaces support two types of virtual network interfaces that differ in how they handle network traffic.
TAP Interfaces (vpptapN)
TAP interfaces operate at Layer 2 (Data Link Layer) and work with complete Ethernet frames. They process full Ethernet packets including MAC addresses and headers, making them suitable for scenarios where you need complete Layer 2 functionality. TAP interfaces can participate in bridging and switching operations, and they provide native support for VLAN tagging and sub-interfaces. This makes them ideal for Layer 2 connectivity, bridging setups, and VLAN segmentation.
TUN Interfaces (vpptunN)
TUN interfaces operate at Layer 3 (Network Layer) and handle raw IP packets without Ethernet headers. They are optimized for Layer 3 routing operations and have lower processing overhead due to their simpler packet structure. TUN interfaces are typically used for VPN tunnels, point-to-point links, and routing applications where Layer 2 functionality is not required.
Choosing the Right Interface Type
The choice between TUN and TAP depends on your specific networking requirements. Use TAP interfaces when you need Layer 2 functionality such as bridging, VLANs, or full Ethernet compatibility. Choose TUN interfaces when you only need Layer 3 functionality for routing or VPN scenarios. While TAP interfaces are more versatile, they have slightly higher overhead compared to TUN interfaces, which are more efficient for pure routing scenarios.
Note
The interface type is determined by the naming convention: vpptapN creates TAP interfaces, while vpptunN creates TUN interfaces. Both support the same configuration commands but behave differently at the packet processing level.
Basic Configuration
Creating a Kernel Interface
Create a kernel interface. The interface name follows the convention vpptapN or vpptunN.
Example:
set vpp kernel-interfaces vpptap1
Interface Description
Set a descriptive name for the kernel interface.
Example:
set vpp kernel-interfaces vpptap1 description "Management interface for VPP bond"
Administrative Control
IP Address Configuration
Configure IPv4 or IPv6 addresses on the kernel interface. Multiple addresses can be assigned.
Examples:
# IPv4 address
set vpp kernel-interfaces vpptap1 address 192.168.1.10/24
# IPv6 address
set vpp kernel-interfaces vpptap1 address 2001:db8::10/64
# Multiple addresses
set vpp kernel-interfaces vpptap1 address 192.168.1.10/24
set vpp kernel-interfaces vpptap1 address 10.0.0.10/8
MTU Configuration
Set the Maximum Transmission Unit (MTU) for the kernel interface. The MTU must be compatible with the connected VPP interface.
Example:
set vpp kernel-interfaces vpptap1 mtu 9000
Note
Ensure the MTU setting matches or is smaller than the MTU supported by the associated VPP interface to avoid issues.
Receive Processing Mode
Configure how the interface processes received packets:
polling: Constantly check for new data (highest performance, higher CPU usage)
interrupt: Interrupt-driven processing (balanced performance and CPU usage)
adaptive: Automatically switch between polling and interrupt based on traffic load
Examples:
# High-performance mode (default)
set vpp kernel-interfaces vpptap1 rx-mode polling
# Balanced mode
set vpp kernel-interfaces vpptap1 rx-mode interrupt
# Adaptive mode
set vpp kernel-interfaces vpptap1 rx-mode adaptive
VLAN Configuration
VPP kernel interfaces support VLAN (Virtual LAN) sub-interfaces for network segmentation.
Creating VLAN Sub-interfaces
Create a VLAN sub-interface with the specified VLAN ID (0-4094).
Example:
set vpp kernel-interfaces vpptap1 vif 100
VLAN Sub-interface Configuration
VLAN sub-interfaces support the same configuration options as the parent interface:
Examples:
# Configure VLAN 100
set vpp kernel-interfaces vpptap1 vif 100 address 192.168.100.1/24
set vpp kernel-interfaces vpptap1 vif 100 description "Management VLAN"
set vpp kernel-interfaces vpptap1 vif 100 mtu 1500
# Configure VLAN 200
set vpp kernel-interfaces vpptap1 vif 200 address 192.168.200.1/24
set vpp kernel-interfaces vpptap1 vif 200 description "Guest VLAN"
Configuration Examples
Basic Kernel Interface
# Create basic kernel interface
set vpp kernel-interfaces vpptap1
set vpp kernel-interfaces vpptap1 description "VPP-Kernel bridge"
set vpp kernel-interfaces vpptap1 address 192.168.1.10/24
set vpp kernel-interfaces vpptap1 mtu 1500
set vpp kernel-interfaces vpptap1 rx-mode adaptive
High-Performance Interface
# High-throughput configuration
set vpp kernel-interfaces vpptap2
set vpp kernel-interfaces vpptap2 description "High-performance bridge"
set vpp kernel-interfaces vpptap2 address 10.0.0.10/8
set vpp kernel-interfaces vpptap2 mtu 9000
set vpp kernel-interfaces vpptap2 rx-mode polling
Multi-VLAN Setup
# Parent interface
set vpp kernel-interfaces vpptap3
set vpp kernel-interfaces vpptap3 description "Multi-VLAN trunk"
# Management VLAN
set vpp kernel-interfaces vpptap3 vif 10
set vpp kernel-interfaces vpptap3 vif 10 address 192.168.10.1/24
set vpp kernel-interfaces vpptap3 vif 10 description "Management network"
# Production VLAN
set vpp kernel-interfaces vpptap3 vif 20
set vpp kernel-interfaces vpptap3 vif 20 address 192.168.20.1/24
set vpp kernel-interfaces vpptap3 vif 20 description "Production network"
# Guest VLAN
set vpp kernel-interfaces vpptap3 vif 30
set vpp kernel-interfaces vpptap3 vif 30 address 192.168.30.1/24
set vpp kernel-interfaces vpptap3 vif 30 description "Guest network"
Bonding Integration
# Create VPP bonding interface
set vpp interfaces bonding bond0
set vpp interfaces bonding bond0 member interface eth0
set vpp interfaces bonding bond0 member interface eth1
set vpp interfaces bonding bond0 kernel-interface vpptap1
# Configure the kernel interface for the bond
set vpp kernel-interfaces vpptap1 address 192.168.1.10/24
set vpp kernel-interfaces vpptap1 description "Bond management interface"
Best Practices
Use kernel interfaces selectively - not every VPP interface needs kernel exposure and also not all VPP interface types support kernel interfaces
Consider the performance impact of copying traffic between VPP and kernel