Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 491)

Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide 467
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Configuring VPLS instances
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• Use the COS value assigned to the VPLS.
The VPLS COS is a configurable option. Show commands will display the COS if it is configured.
If the COS value it is not configured, the show commands will not display any COS value.
When a COS value is set for the VPLS, the device selects a tunnel LSP that also has this COS
value, when one is available. When no tunnel LSP with this COS value is available, the device
selects a tunnel LSP with the highest configured COS value (although never higher than the
COS setting for the VPLS).
When the selected tunnel LSP does not have a COS value, the VPLS configured COS value is
used to provide QoS. The VPLS COS value is mapped to a value in the EXP field. This allows
traffic multiple VPLS using a single tunnel LSP, traffic from each VPLS can receive different
QoS treatment.
• Use the priority in the packet’s 802.1q tag.
When neither the tunnel LSP nor the VPLS has a configured COS value, the device examines
the priority in the Layer 2 packet's 802.1q tag, when the packet has one. Consequently, Layer 2
packets with the same 802.1q priority receive the same QoS in the VPLS.
• Use the configured priority of the port.
When neither the tunnel LSP nor the VPLS has a configured COS value, and the Layer 2 packet
does not have an 802.1q priority, QoS can be provided based on the priority of the incoming
port. A port can be assigned a priority from zero (0) (lowest priority) to seven (7) (highest
priority). The default port priority is zero (0).
By assigning different priorities to the ports where customer edge (CE) devices are connected
(that is, the VPLS endpoints), the user can provide QoS to untagged Layer 2 traffic received
from different customer locations.
When a packet enters a VPLS, the PE router that serves as both the VPLS endpoint and the ingress
of a tunnel LSP pushes two labels onto the packet the inner VC label and the outer tunnel label.
The packet’s priority resides in the EXP field of the MPLS label header. The VC label and the tunnel
label carry the same value in the EXP field.
The following table lists how a Layer 2 packet’s priority is mapped to a value in the EXP field and
how the EXP value is mapped to a priority queue.
Tunnel LSP configured COS or
VPLS configured COS or
802.1q priority or
Configured port priority Value placed in the tunnel and VC
label EXP field Priority queue
7 7 qosp7 (highest priority)
6 6 qosp6
5 5 qosp5
4 4 qosp4
3 3 qosp3
2 2 qosp2
1 1 qosp1
0 0 qosp0 (best effort)