Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
© 2019 Extreme Networks, Inc. All rights reserved. 132
With today’s platforms, which can act both as L2 and L3 switches, when an ingress packet is received
carrying both DSCP and 802.1Q-Tag 802.1p-bit QoS markings, the default behavior is to QoS classify using
the markings that correspond to the way in which the packet will be forwarded. Hence a packet that is L2
switched (bridged) within the VLAN (or L2 VSN) will use the p-bits to derive the QoS PHB, while a packet
that is L3 switched (IP routed) will use the DSCP markings to derive the QoS PHB.
Tip
On Extreme Networks ERS, VSP and ExtremeXOS platforms, a port can be independently
configured as L2-Trusted or L2-Untrusted, and L3-Trusted or L3-Untrusted. An L2-
Untrusted + L3-Trusted configuration will ensure that DSCP is used to derive QoS even on
L2 switched traffic.
Table 12 illustrates the DiffServ DSCP & PHB defined in RFC 4594 as well as their corresponding mapping to
802.1p priority levels and how these service classes are normally handled in the Extreme Networks
switching platforms.
Table 12 – QoS Markings and Queuing Profiles
Class of Service
(CoS) and ERS and
VSP Naming
Classification
Description
PHB
DSCP
802.1p
CoS 7 Network/Critical
CS7, CS6
48, 56
7
Network Control – Strict Queue, 5-10%
shaped
CoS 6 Premium
EF, CS5
46, 40
6
Real Time Voice – Strict Queue, 50% shaped
CoS 5 Platinum
AF4x
1
, CS4
34,36,38,32
5
Real Time Video – WRR Queue
CoS 4 Gold
AF3x
1
, CS3
26,28,30,24
4
Non-Real Time Streaming – WRR Queue
CoS 3 Silver
AF2x
1
, CS2
18,20,22,16
3
Non-Real Time – WRR Queue
CoS 2 Bronze
AF1x
1
, CS1
10,12,14,8
2
Non-Real Time – WRR Queue
CoS 1 Standard (Default)
DF, CS0
0 - 4
0
Best Effort – WRR Queue
CoS 0 Custom
n/a
n/a
1
Scavenger – Low Priority Queue
1
where x can take value 1,2,3 depending on the Drop Precedence
It should be noted that not all QoS classes need be used. The DiffServ model is a template that defines as
many classes of traffic with unique QoS requirements as possible and the Extreme Networks VSP, ERS, and
ExtremeXOS series QoS product implementation allows up to an eight-class model. In this model, the
Network/Critical class is always present and reserved exclusively for network control protocols (for
instance, IS-IS with Fabric Connect), and in the absence of any QoS policies all application and user traffic
will use the default Best Effort queue.
The network design should take into consideration the applications, traffic types, and virtual networks to be
transported as well as how critical each one of those is for the business. Based on that analysis, the QoS
policy will define the class to use for each virtual network or application within.