Brocade Fabric OS FCIP Administrator's Guide v7.1.0 (53-1002748-01, March 2013)

26 Fabric OS FCIP Administrator’s Guide
53-1002748-01
QoS, DSCP, and VLANs
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DSCP settings are useful only if IP routers are configured to enforce QoS policies uniformly within
the network. IP routers use the DSCP value as an index into a Per Hop Behavior (PHB) table. Control
connections and data connections can be configured with different DSCP values. Before
configuring DSCP settings, determine if the IP network you are using implements PHB, and consult
with the WAN administrator to determine the appropriate DSCP values.
VLANs and Layer 2 Quality of Service
Devices in physical LANs are constrained by LAN boundaries. They are usually in close proximity to
each other, and share the same broadcast and multicast domains. Physical LANs often contain
devices and applications that have no logical relationship. Also, when logically related devices and
applications reside in separate LAN domains, they must be routed from one domain to the other.
A VLAN is a virtual local area network. A VLAN can reside within a single physical network, or it can
span several physical networks. Related devices and applications that are separated by physical
LAN boundaries can reside in the same VLAN. Also, a large physical network can be broken into
smaller VLANs. VLAN traffic is routed using 802.1Q-compliant tags within an Ethernet frame. The
tag includes a unique VLAN ID, and Class of Service (CoS) priority bits. The CoS priority scheme
(also called Layer 2 Class of Service or L2CoS) uses three Class of Service (CoS or 802.1P) priority
bits, allowing eight priorities. Consult with your WAN administrator to determine usage.
When both DSCP and L2CoS are used
If an FCIP tunnel or circuit is VLAN tagged, both DSCP and L2CoS are relevant, unless the VLAN is
end-to-end, with no intermediate hops in the IP network. Table 4 shows the default mapping of
DSCP priorities to L2CoS priorities. This may be helpful when consulting with the network
administrator. These values are modified on a per-FCIP circuit basis for the 7800 switch and
FX8-24 blade.
TABLE 4 Default mapping of DSCP priorities to L2CoS priorities
DSCP priority/bits L2CoS priority/bits Assigned to:
46 / 101110 7 / 111 Class F
7 / 000111 1 / 001 Medium QoS
11 / 001011 3 / 011 Medium QoS
15 / 001111 3 / 011 Medium QoS
19 / 010011 3 / 011 Medium QoS
23 / 010111 3 / 011 Medium QoS
27 / 011011 0 / 000 Class 3 Multicast
31 / 011111 0 / 000 Broadcast/Multicast
35 / 100011 0 / 000 Low Qos
39 / 100111 0 / 000 Low Qos
43 / 101011 4 / 100 High QoS
47 / 101111 4 / 100 High QoS
51 / 110011 4 / 100 High QoS
55 / 110111 4 / 100 High QoS