VXLAN
VXLAN provides the same Ethernet Layer 2 network services as VLAN does today, but with greater
extensibility and flexibility. It is a Layer 2 overlay scheme over a Layer 3 network. It uses MAC
Address-in-User Datagram Protocol (MAC-in-UDP) encapsulation to provide a means to extend Layer 2
segments across the core network. VXLAN is a solution to support a flexible, large-scale multitenant
environment over a shared common physical infrastructure. The transport protocol over the core network is
IP plus UDP. Compared to VLAN, VXLAN offers the following benefits:
• Flexible placement of multitenant segments throughout the data center: It provides a solution to extend
Layer 2 segments over the underlying shared network infrastructure so that tenant workload can be placed
across physical pods in the data center.
• Higher scalability to address more Layer 2 segments: VLANs use a 12-bit VLAN ID to address Layer
2 segments, which results in limiting scalability of only 4094 VLANs. VXLAN uses a 24-bit segment
ID known as the VXLAN network identifier (VNID), which enables up to 16 million VXLAN segments
to co-exist in the same administrative domain.
• Better utilization of available network paths in the underlying infrastructure: VLAN uses the Spanning
Tree Protocol for loop prevention, which ends up not using half of the network links in a network by
blocking redundant paths. In contrast, VXLAN packets are transferred through the underlying network
based on its Layer 3 header and can take complete advantage of Layer 3 routing, equal-cost multipath
(ECMP) routing, and link aggregation protocols to use all available paths.
VXLAN Anycast Gateway
The VXLAN anycast gateway feature extends anycast functionality to VXLAN. It enables the use of anycast
routing on a network for underlay multicast load-balancing and redundancy.
The VXLAN anycast solution:
• Allows true active-active first hop gateways (active-active on a per flow basis).
• Does not involve any new control or management plane protocols or any form of external SDN controllers
or NMS to co-ordinate and synchronize gateways.
The anycast gateway feature follows these basic concepts:
• Creating a virtual Layer 3 gateway and a virtual VTEP across multiple VXLAN gateways. These gateways
use an identical configuration of an overlay IP address, overlay MAC address, and underlay VTEP IP
address.
• Creating a private multicast group between the gateways to use as a data plane mirror for certain types
of overlay control packets.
The VXLAN anycast gateway feature is supported on only Cisco ASR 9000 High Density 100GE Ethernet
line cards.
Note
Recommendations
These are the recommendations that users must consider before configuring VXLAN anycast gateway feature:
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
474
Implementing VXLAN
VXLAN
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