Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
© 2019 Extreme Networks, Inc. All rights reserved. 135
class marking, so that subsequent transport (BCB) hops along the SPB path will be able to derive the
correct PHB by only looking at those Backbone p-bits. This will include the egress BEB node, which will
remove the Mac-in-Mac encapsulation, and at which point the DSCP markings will continue to be relevant
to any subsequent IP routing hops (either external or internal to the SPB Fabric) encountered.
Figure 79 SPB QoS Uniform Model
Note
The Uniform model takes its name from the same model described for MPLS in RFC 3270.
Both models can be combined on the same SPB backbone for different VSN services. However, in an
Enterprise environment, the Uniform model is the most applicable and is therefore the model we will look at
in more detail.
In the Extreme Networks Fabric Connect solution, the SPB fabric can also be extended to non-Mac-in-Mac
capable devices using Fabric Attach, as illustrated in Figure 79. With Fabric Attach, both the FA-
Client/Proxy and FA-Server will automatically Trust DSCP (and native VLAN tag p-bits) QoS markings on
their FA/UNI interconnect and the FA-Server will automatically map those markings into the corresponding
Backbone p-bit marking for the PHB class. There is, in fact, nothing to configure to make this happen and
the only QoS configuration required will be on the access ports where users connect (typically located on
an FA Proxy switch access ports) or where servers connect in the data center (typically on an SPB DVR
BEB node) or where firewalls connect (either in the DMZ or in the data center). The QoS policy will
determine whether the traffic received from these end devices can be trusted (in which case the access
ports are configured as Trusted ports) or not (in which case the access ports are configured as Untrusted
ports with access policies to selectively assign the appropriate QoS service class based on ACL filter hits).
In the case of an ExtremeXOS access layer, advanced policies can be used to automatically assign the
correct QoS markings to traffic profiles defined in Extreme Management Center and either statically
assigned to ports or assigned via LLDP with CEP (Convergence End-Point Detection), or via ExtremeCloud
with dynamic assignment.
Tip
Benefits of SPB’s QoS model over MPLS QoS based on the Experimental QoS bits:
With MPLS QoS there is a lot of complexity, and additional configuration required on the
egress PE to accommodate the use of Penultimate Hop Popping (PHP), whereby the
penultimate hop in the MPLS backbone removes the MPLS labels from the packets before
these reach the last LSP hop (i.e., the PE node.) This is done to avoid packet recycling
(double lookup) on the egress PE node, which would otherwise have a forwarding
performance impact on the PE. The problem is that the MPLS QoS Experimental bits are
contained in the label and are thus thrown away by PHP. Much of RFC 3270 discusses how
to resolve this problem as this applies to both the Pipe and Uniform models. With SPB,
there is no such inconvenience as PHP.