Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
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Caution
Fabric Extend in L2 mode does not support IEEE 802.1ad Q-in-Q; only IEEE 802.1Q-tags
are supported.
This has some implications in that we know that an SPB Ethernet Fabric will emit traffic with 802.1Q-tags
for any and all of the BVLANs it was provisioned with. The first problem is that the SPB BVLAN IDs are
globally configured and have to be the same across the entire SPB Fabric, which does not square with the
need to change that same Q-tag to differentiate between the various WAN circuits arriving on the same
port. This first problem is resolved by the Fabric Extend logical IS-IS interface capability to implement
VLAN translation when used in Fabric Extend L2 mode. In other words, for a given point-to-point WAN
circuit, the BVLAN Q-tags will be translated to a different pair of Q-tag values that will be unique to that
circuit and different from other Q-tag value pairs used for other WAN circuits terminating on the same
logical IS-IS Ethernet port.
The second problem is that use of an 802.1Q encapsulation means that the WAN provider is not able to
hide the various SPB BVLAN Q-tags behind a single outer Q-in-Q tag service. Instead a number of circuits
equal to the number of BVLANs will need to be provided in parallel between each pair of Fabric Extend
nodes. This is depicted in Figure 60 by the double colored bricks terminating each circuit. Configuration of
a Fabric Extend end-point on a logical IS-IS interface will thus require two VLAN-tags, one for the Primary
BVLAN and one for the Secondary BVLAN.
Note
Extreme’s Fabric Connect currently support a maximum of two BVLANs, but support of up
to 16 BVLANs will become available in future software versions. However, when 16 BVLAN
support is added, it is expected that this will be able to co-exist with other parts of the
same SPB Fabric where only two BVLANs are in use. Use of more than two BVLANs will
typically only provide benefits in the data center for spine-leaf architectures and will not
be used in the wider campus and branch fabric.
A further point of consideration has to do with the outer Ethernet Ethertype encoding used. The correct
SPB Mac-in-Mac encapsulation Ethertype value is hexadecimal 88:a8, which is the same Ethertype used
with IEEE 802.1ad Q-in-Q but is different from the 81:00 hexadecimal value that is typically expected on
IEEE 802.1Q interfaces. The WAN circuits may thus not accept SPB traffic arriving with an 88:a8 Ethertype
on an IEEE 802.1Q interface.
Tip
All Extreme Networks SPB capable platforms are able to process and receive Mac-in-Mac
traffic using either 88:a8 or 81:00 Ethertype.
All Extreme Networks SPB-capable platforms can be globally configured to use either
88:a8 or 81:00 Ethertype when (acting as a BEB) they generate Mac-in-Mac encapsulated
traffic. By default, 81:00 Ethertype is used. The Ethertype can be changed dynamically
without any operational impact.
Clearly Fabric Extend L2 mode is not as flexible as the Fabric Extend L3 modes where an IP encapsulation
(VXLAN or IPsec) is used. It does however present an advantage over the other Fabric Extend modes in
that the Extreme Networks VSP4450/4850 platforms could be deployed without the additional cost of an
Open Network Adapter (ONA).
VSN Extend with VXLAN Gateway
The VXLAN Gateway functionality brings the ability to interconnect virtualized L2 segments in a VXLAN
overlay with virtualized L2 segments in the Extreme Fabric Connect architecture.