The QoS Policy Propagation through BGP (QPPB) is a feature that allows a QoS treatment (forwarding class and optionally priority) to be associated with a BGP IPv4, label-IPv4, IPv6, or label-IPv6 route that is installed in the routing table. This is done so that when traffic arrives on a QPPB-enabled IP interface and its source or destination IP address matches a BGP route with QoS information, the packet is handled according to the QoS of the matching route. SR OS supports QPPB on the following types of interfaces:
base router network interfaces
IES and VPRN SAP interfaces
IES and VPRN spoke SDP interfaces
IES and VPRN subscriber interfaces
QPPB is enabled on an interface using the qos-route-lookup command. There are separate commands for IPv4 and IPv6 so QPPB can be enabled in one mode, source, destination, or none, for IPv4 packets arriving on the interface, and a different mode source, destination, or none, for IPv6 packets arriving on the interface.
Different BGP routes for the same IP prefix can be associated with different QPPB information. If these BGP routes are combined in support of ECMP or BGP fast reroute then the QPPB information becomes next-hop specific. If these LOC-RIB routes are combined in support of ECMP or BGP fast reroute then the QPPB information becomes next-hop specific. This means that in destination QPPB mode the QoS assigned to a packet depends on the BGP next-hop that is selected for that particular packet by the ECMP hash or fast reroute algorithm. In source QPPB mode the QoS assigned to a packet comes from the first BGP next-hop of the IP route matching the source address.