VXLAN

Virtual Extensible LAN (VXLAN) as defined in RFC 7348 is an overlay technology designed to provide Layer 2 and Layer 3 connectivity services over a generic IP network. IP networks provide increased scalability, balanced performance and predictable failure recovery. VXLAN achieves this by tunneling Layer 2 frames inside of IP packets. VXLAN requires only IP reachability between the VXLAN edge devices, provided by an IP routing protocol.

VXLAN uses an 8-byte header that consists of a 24-bit identifier (VNID) and multiple reserved bits. The VXLAN header, along with the original Ethernet frame, is placed in the UDP payload. The 24-bit VNID is used to identify Layer 2 segments and to maintain. Layer 2 isolation between the segments. With 24 bits allocated for the VNID, VXLAN can support up to 16 million logical segments.

The terminology used when describing the key components of a VXLAN Fabric include:

VTEP — Virtual Tunnel Endpoint The hardware or software element at the edge of the network responsible for instantiating the VXLAN tunnel and performing VXLAN encapsulation and decapsulation

VNI — Virtual Network Instance a logical network instance providing Layer 2 or Layer 3 services and defining a Layer 2 broadcast domain

VNID — Virtual Network Identifier a 24-bit segment ID that allows the addressing of up to 16 million logical networks to be present in the same administrative domain

Bridge Domain A set of logical or physical ports that share the same flooding or broadcast characteristics

The VXLAN tunnel endpoint function can be performed by a hardware device or by a software entity such as a hypervisor. The main advantage of using a hardware-based tunnel endpoint is the enhanced performance offered through the capabilities of the switch ASICs.

VXLAN control plane

• Static VXLAN tunnel simple mapping and doployment for small data center
• VXLAN EVPN tunnel using BGP as control plane bgp will advertise information about VTEP

Virtual Extensible LAN Virtual Extensible LAN (VXLAN) is widely deployed in many L3 data centers to provide L2 connectivity between hosts for specific applications. This is done by encapsulating L2 frames in L3 packets. VXLAN is an Overlay Technology as it allows you to stretch L2 connections over an intervening L3 network by encapsulating (tunneling) Ethernet frames in an IP-UDP packet with a VXLAN header.

VTEP while sending traffic takes end host traffic in vlan maps to vxlan vni then encapsulates it in vxlan. When receiving traffic from remote vxlan vtep decapsulates the vxlan packet and send it to attached host

VXLAN Flood and learn

client arp request is flooded to vlan and vni to another remote VTEP

EVPN as a contol plane

commonly bgp evpn RFC 7432

EVPN routes

Type-2 Mac / ip route

type-3 inclusive multicast ethernet tag route

Type-5 ip prefix route

VXLAN id is global significant must same between VTEP

vlan id is local significant

VXLAN BGP EVPN Architecture

Configuration FLOW static vxlan tunnel

1. Create vlan
2. mapping vlan on leaf switch
3. Create vxlan interface
4. Create vxlan local & remote IPv4
5. mapping vlan to VXLAN

BUM (broadcast unknown unicast)

VXLAN, or Virtual eXtensible LAN, is an overlay network that runs on top of an existing IP network. VXLAN has a number of different use cases, including creating a massively scalable network (up to 16.7 million possible networks) and connecting data centers at layer 2 across a layer 3 network. VXLAN encapsulates frames with layer 3/4 (IP/UDP), sending them over both layer 2 and layer 3 networks. The benefits of VXLAN on layer 2 (IP) networks are global addressing, better scale, more resiliency, and better use of available bandwidth.

The connections between endpoints are called VXLAN tunnels. These VXLAN tunnels are encapsulating traffic as it flows across the network between the VXLAN tunnel endpoints (also called VTEPs, or VXLAN Tunnel EndPoints). The VXLAN encapsulation allows for the transport of traffic over networks that end hosts do not need knowledge of. This means a host could send an ARP request to another host, across the network, through a VxLAN tunnel, and never know about the VxLAN tunnel or the underlay network it travels through.

VTEPs can be implemented in hardware or software. The configuration of VTEPs and creation of the overlay networks is typically implemented using a commercial controller, such as VMware NSX or Midokura MidoNet, or using a protocol such as BGP EVPN over VXLAN (explained in the next chapter). However, some people build their own special purpose controllers. Regardless of which of these techniques you use, Linux provides the underlying VTEP building block.