DSCP Preserve
Layer 3 VPN services use the DSCP field in the IP header to convey QoS information, determining packet priority and treatment (e.g., DSCP 46 for high-priority voice traffic). When L3 VPN traffic enters the MPLS domain, QoS is managed by the EXP field in the MPLS label, typically derived from the DSCP value. In Qumran-based systems, the EXP field is updated based on the remarked DSCP value. By default, remarking the DSCP at the access interface affects both the IP header DSCP field and the MPLS EXP field. Service managers need control over whether to remark the DSCP or not while configuring EXP field updates.
Network operator can control preserving DSCP in the edge routers at gobal level or per VRF level or combination of both. To provide more control, the following DSCP preservation settings are available:
| • | DSCP Preserve Global - When DSCP preserve is enabled globally, it applies to all VRFs, preserving the DSCP value even if remarking is configured. |
| • | DSCP Preserve Per-VRF - Per-VRF configuration allows DSCP preservation only for specific VPN services, offering more granular control for network administrators. |
DSCP Preserve Behavior: Below table shows the way DSCP preserve global and per VRF configuration impact the DSCP value of the traffic received on the VRF of interest when dscp-to-queue profile is updated with remark DSCP option.
|
DSCP-preserve |
per-vrf not configured |
per-vrf enabled |
per-vrf disabled |
|
Global enable |
preserved |
preserved |
not preserved |
|
Global disable |
not preserved |
preserved |
not preserved |
Network administrators can further refine control using global or custom DSCP-to-queue profiles and policy-map configurations to remark DSCP values based on specific match criteria. This provides flexible and tailored QoS management across different VPN services.
DSCP Preserve Characteristics
| • | QoS information mapping ensures that the QoS information carried in the DSCP field of the IP header is correctly mapped to the MPLS EXP field. |
| • | DSCP remarking controls whether the DSCP value in the IP header is remarked at the access interface, affecting both customer traffic and the MPLS domain. |
| • | In hardware like Qumran, the EXP field update is based on the remarked DSCP value, requiring configuration to manage how and if DSCP values are modified. |
| • | Ingress configuration requirement introduces the need for ingress-side configuration to properly align the DSCP and EXP field values, ensuring correct QoS handling. |
| • | DSCP preserve provides service managers with control over whether DSCP values are modified or preserved during the process of mapping to MPLS headers. |