VLANS have been around ever since I have
been in networking, providing a network segregation function at Layer 2.
802.1q is the IEEE standard that defines VLAN
tagging. In summary a 32 bit field is added between
source MAC and Ether Type field in an Ethernet Frame. 12 bits of this field were set aside for the
VLAN id, so enabling 4094 vlans.
In hindsight only setting aside 12 bits to
the VLAN id could now be viewed as an oversight. Today especially in the Cloud Infrastructure
space, single physical topologies, have now become multi tenanted spaces each
requiring their own isolated network. 4094
vlans has become a constraint.
Additionally when the VLAN concept was
derived it was designed to run in a ‘localised’ environment. Today there are
requirements for multiple physical environments to be logically connected at
L2.
VXLAN or Virtual eXtensible LANs aim to
build upon the existing VLAN concept but solve some of the problems described.
Firstly the VXLAN id is 24 bits, doubling the old VLAN id field size, and
enabling over 16 million VLAN ids.
Secondly VXLAN extends the reach of VLAN by enabling VLANs to be
transported or encapsulation over an IP, Layer 3 routed domain.
VXLAN does not represent the only solution
to the VLAN limitations of 802.1Q. I
hope to post on some of the other solutions available.
