Alcatel-Lucent 7750 SR-OS, Руководство по настройке

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IP Router Configuration
7750 SR OS Router Configuration Guide Page 25
QoS Policy Propagation Using BGP (QPPB)
This section discusses QPPB as it applies to VPRN, IES, and router interfaces. Refer to the
Internet Enhanced Service section in the Services Guide and the IP Router Configuration section
in the 7x50 SR OS Router Configuration Guide.
QoS policy propagation using BGP (QPPB) is a feature that allows a route to be installed in the
routing table with a forwarding-class and priority so that packets matching the route can receive
the associated QoS. The forwarding-class and priority associated with a BGP route are set using
BGP import route policies. In the industry this feature is called QPPB, and even though the feature
name refers to BGP specifically. On SR routers, QPPB is supported for BGP (IPv4, IPv6, VPN-
IPv4, VPN-IPv6), RIP and static routes.
While SAP ingress and network QoS policies can achieve the same end result as QPPB, assigning
a packet arriving on a particular IP interface to a specific forwarding-class and priority/profile
based on the source IP address or destination IP address of the packet ?the effort involved in
creating the QoS policies, keeping them up-to-date, and applying them across many nodes is much
greater than with QPPB. In a typical application of QPPB, a BGP route is advertised with a BGP
community attribute that conveys a particular QoS. Routers that receive the advertisement accept
the route into their routing table and set the forwarding-class and priority of the route from the
community attribute.
QPPB Applications
There are two typical applications of QPPB:
1. Coordination of QoS policies between different administrative domains.
2. Traffic differentiation within a single domain, based on route characteristics.
Inter-AS Coordination of QoS Policies
The operator of an administrative domain A can use QPPB to signal to a peer administrative
domain B that traffic sent to certain prefixes advertised by domain A should receive a particular
QoS treatment in domain B. More specifically, an ASBR of domain A can advertise a prefix XYZ
to domain B and include a BGP community attribute with the route. The community value implies
a particular QoS treatment, as agreed by the two domains (in their peering agreement or service
level agreement, for example). When the ASBR and other routers in domain B accept and install
the route for XYZ into their routing table, they apply a QoS policy on selected interfaces that
classifies traffic towards network XYZ into the QoS class implied by the BGP community value.
QPPB may also be used to request that traffic sourced from certain networks receive appropriate
QoS handling in downstream nodes that may span different administrative domains. This can be