linux-sg2042/Documentation/networking/vxlan.rst

.. SPDX-License-Identifier: GPL-2.0

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Virtual eXtensible Local Area Networking documentation
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The VXLAN protocol is a tunnelling protocol designed to solve the
problem of limited VLAN IDs (4096) in IEEE 802.1q.  With VXLAN the
size of the identifier is expanded to 24 bits (16777216).

VXLAN is described by IETF RFC 7348, and has been implemented by a
number of vendors.  The protocol runs over UDP using a single
destination port.  This document describes the Linux kernel tunnel
device, there is also a separate implementation of VXLAN for
Openvswitch.

Unlike most tunnels, a VXLAN is a 1 to N network, not just point to
point. A VXLAN device can learn the IP address of the other endpoint
either dynamically in a manner similar to a learning bridge, or make
use of statically-configured forwarding entries.

The management of vxlan is done in a manner similar to its two closest
neighbors GRE and VLAN. Configuring VXLAN requires the version of
iproute2 that matches the kernel release where VXLAN was first merged
upstream.

1. Create vxlan device::

    # ip link add vxlan0 type vxlan id 42 group 239.1.1.1 dev eth1 dstport 4789

This creates a new device named vxlan0.  The device uses the multicast
group 239.1.1.1 over eth1 to handle traffic for which there is no
entry in the forwarding table.  The destination port number is set to
the IANA-assigned value of 4789.  The Linux implementation of VXLAN
pre-dates the IANA's selection of a standard destination port number
and uses the Linux-selected value by default to maintain backwards
compatibility.

2. Delete vxlan device::

    # ip link delete vxlan0

3. Show vxlan info::

    # ip -d link show vxlan0

It is possible to create, destroy and display the vxlan
forwarding table using the new bridge command.

1. Create forwarding table entry::

    # bridge fdb add to 00:17:42:8a:b4:05 dst 192.19.0.2 dev vxlan0

2. Delete forwarding table entry::

    # bridge fdb delete 00:17:42:8a:b4:05 dev vxlan0

3. Show forwarding table::

    # bridge fdb show dev vxlan0

The following NIC features may indicate support for UDP tunnel-related
offloads (most commonly VXLAN features, but support for a particular
encapsulation protocol is NIC specific):

 - `tx-udp_tnl-segmentation`
 - `tx-udp_tnl-csum-segmentation`
    ability to perform TCP segmentation offload of UDP encapsulated frames

 - `rx-udp_tunnel-port-offload`
    receive side parsing of UDP encapsulated frames which allows NICs to
    perform protocol-aware offloads, like checksum validation offload of
    inner frames (only needed by NICs without protocol-agnostic offloads)

For devices supporting `rx-udp_tunnel-port-offload` the list of currently
offloaded ports can be interrogated with `ethtool`::

  $ ethtool --show-tunnels eth0
  Tunnel information for eth0:
    UDP port table 0:
      Size: 4
      Types: vxlan
      No entries
    UDP port table 1:
      Size: 4
      Types: geneve, vxlan-gpe
      Entries (1):
          port 1230, vxlan-gpe