Juniper MX Series

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 ...