IP Router Configuration
Router Configuration Guide 19
Traffic Differentiation Based on Route Characteristics
There may be times when a network operator wants to provide differentiated service to
certain traffic flows within its network, and these traffic flows can be identified with known
routes. For example, the operator of an ISP network may want to give priority to traffic
originating in a particular ASN (the ASN of a content provider offering over-the-top services
to the ISP’s customers), following a certain AS_PATH, or destined for a particular next-hop
(remaining on-net vs. off-net).
Figure 1 shows an example of an ISP that has an agreement with the content provider
managing AS300 to provide traffic sourced and terminating within AS300 with differentiated
service appropriate to the content being transported. In this example we presume that ASBR1
and ASBR2 mark the DSCP of packets terminating and sourced, respectively, in AS300 so
that other nodes within the ISP’s network do not need to rely on QPPB to determine the
correct forwarding-class to use for the traffic. The DSCP or other COS markings could be left
unchanged in the ISP’s network and QPPB used on every node.
Figure 1: Use of QPPB to Differentiate Traffic in an ISP Network
QPPB
There are two main aspects of the QPPB feature:
• The ability to associate a forwarding-class and priority with certain routes in the
routing table.
• The ability to classify an IP packet arriving on a particular IP interface to the
forwarding-class and priority associated with the route that best matches the packet.
OSSG639
P
PE 1 ASBR 1
ASBR 2
Peer
AS 200
Provider
Content Provider
AS 300
Route Policy:
Accept all routes with AS_PATH
ending with ASN 300 and set fcto
high-1
QoSPolicy:
Lookup the destination IP address
of all packets arriving on this
interface to determine fc
Route Policy:
Accept all routes with AS_PATH
ending with ASN 300 and set fcto
high-1
QoSPolicy:
Lookup the source IP address of all
packets arriving on this interface to
determine fc
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