Cisco ASR 9000 Series Routing Configuration Guide

Aggregator: 304 34.3.3.3
Atomic Aggregator
Community: 1:60042 2:41661 3:47008 4:9280 5:39778 6:1069 7:15918 8:8994 9:52701
10:10268 11:26276 12:8506 13:7131 14:65464 15:14304 16:33615 17:54991 18:40149 19:19401
Extended community: RT:100:1 RT:1.1.1.1:1]
Flow-tag propagation
The flow-tag propagation feature enables you to establish a co-relation between route-policies and user-policies.
Flow-tag propagation using BGP allows user-side traffic-steering based on routing attributes such as, AS
number, prefix lists, community strings and extended communities. Flow-tag is a logical numeric identifier
that is distributed through RIB as one of the routing attribute of FIB entry in the FIB lookup table. A flow-tag
is instantiated using the 'set' operation from RPL and is referenced in the C3PL PBR policy, where it is
associated with actions (policy-rules) against the flow-tag value.
You can use flow-tag propagation to:
•
Classify traffic based on destination IP addresses (using the Community number) or based on prefixes
(using Community number or AS number).
•
Select a TE-group that matches the cost of the path to reach a service-edge based on customer site service
level agreements (SLA).
•
Apply traffic policy (TE-group selection) for specific customers based on SLA with its clients.
•
Divert traffic to application or cache server.
For more information on the commands for flow-tag propagation see the BGP Commands module in the
Cisco ASR 9000 Series Aggregation Services Router Routing Command Reference.
Restrictions for flow-tag propagation
Some restrictions are placed with regard to using Quality-of-service Policy Propagation Using Border Gateway
Protocol (QPPB) and flow-tag feature together in a ASR9K platform. These include:
•
A route-policy can have either 'set qos-group' or 'set flow-tag,' but not both for a prefix-set.
•
Route policy for qos-group and route policy flow-tag cannot have overlapping routes. The QPPB and
flow tag features can coexist (on same as well as on different interfaces) as long as the route policy used
by them do not have any overlapping route.
•
Mixing usage of qos-group and flow-tag in route-policy and policy-map is not recommended.
Source and destination-based flow tag
The source-based flow tag feature allows you to match packets based on the flow-tag assigned to the source
address of the incoming packets. Once matched, you can then apply any supported PBR action on this policy.
Configure Source and Destination-based Flow Tag
This task applies flow-tag to a specified interface. The packets are matched based on the flow-tag assigned
to the source address of the incoming packets.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
135
Implementing BGP
Flow-tag propagation

Cisco ASR 9000 Series Specifications

General

Brand	Cisco
Model	ASR 9000 Series
Category	Network Router
Language	English