VCP Interface Class of Service

Depending on the traffic patterns in the network, it’s possible to cause congestion on the VCP interfaces. Recall that the VCP interfaces should be sized to roughly 50% of the total aggregate transit traffic flowing through the member. Even with properly sized VCP interfaces, it’s just a fact of life that there are microbursts of traffic that will cause an interface to become congested. It’s important to remember that in addition to inter-member transit traffic, the VCP interfaces also transmit the VCCP control traffic. If and when the VCP interfaces become congested due to microbursts of traffic, there needs to be a guarantee in place that gives control traffic priority so that the virtual chassis isn’t negatively impacted.

VCP Traffic Encapsulation

All traffic that’s transmitted across the VCP interfaces is encapsulated in an IEEE 802.1Q header that allows VCP to set the proper IEEE 802.1p code points for traffic differentiation. There are various types of traffic that use the VCP interfaces, as shown in Table 6-5.

Table 6-5. VCP Interface Traffic to IEEE 802.1p Mapping.

Traffic

Forwarding Class

Packet Loss Priority

IEEE 802.1p Code Point

PFE ↔ PFE

best-effort

Low

000

PFE ↔ PFE

best-effort

High

001

PFE ↔ PFE

assured-forwarding

Low

010

PFE ↔ PFE

assured-forwarding

High

011

PFE ↔ PFE

expedited-forwarding

Low

100

PFE ↔ PFE

expedited-forwarding

High

101

RE ↔ RE and RE ↔ PFE

network-control

Low

110

VCCP

network-control

High

111

As transit traffic flows across VCP interfaces, there could be ...

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