TE Tunnel Attributes 251
NOTE Prior to deploying TE in a network, it is important to profile the traffic flow patterns and
statistics at various points in the network. You can do this using offline tools and techniques
that are beyond the scope of this book. The goal is to come up with a traffic model that best
optimizes the network resources.
TE Trunk Definition
The TE trunk defines the class of packets carried on a TE tunnel. This policy is local to the
head-end router originating the TE tunnel setup.
As discussed in Chapter 3, “Network Boundary Traffic Conditioners: Packet Classifier,
Marker, and Traffic Rate Management,” a traffic class is defined flexibly based on the
Transmission Control Protocol/Internet Protocol (TCP/IP) traffic headers. A traffic class
can be based on a single parameter, such as the IP destination or the MPLS Class of Service
(CoS) field, or on a number of parameters, such as all File Transfer Protocol (FTP) traffic
going from a certain sender to a specific destination. In RRR, all packets of a traffic class
take a specified defined or dynamically determined common path across a network. For this
reason, RRR traffic classes are also termed traffic trunks.
TE Tunnel Attributes
A TE tunnel is given attributes to describe the traffic trunk’s requirements and to specify
various administrative policies. This section discusses the various tunnel attributes.
The bandwidth attribute shows the end-to-end bandwidth required by a TE tunnel. You can
define it based on the requirements of the traffic class being carried within the TE tunnel.
Setup and Holding Priorities
The setup and holding priorities are used for admission control. Holding priority
determines priority for holding a resource, whereas setup priority determines priority for
taking a resource.
When resources are in contention, a new tunnel with a high setup priority can preempt all
established tunnels in the path with a holding priority less than the new tunnel’s setup
priority. An established TE tunnel with the highest holding priority cannot be preempted.
252 Chapter 10: MPLS Traffic Engineering
Table 10-1 shows the implications of the low and high values for TE tunnel setup and
holding priorities.
Resource Class Affinity
The resource class affinity attribute provides a means to apply path selection policy by
administratively including or excluding specific links in the network. This resource class
affinity attribute consists of a 32-bit resource affinity attribute and a 32-bit resource class
mask. The resource affinity attribute indicates whether to include or exclude a specific link
in the path computation process. Each link carries a resource class attribute, which defaults
to 0x00000000 unless it is explicitly specified. The resource class mask shows the
interesting bits of the resource class link attribute. The resource class, the resource class
mask, and the resource class affinity attributes are related to each other as follows:
Resource Class & Resource Class Mask == Resource Class Affinity
& indicates a bit-wise logical AND operation and
== indicates a bit-wise logical equality.
Table 10-2 tabulates the link inclusion or exclusion policy in a TE tunnel path selection
based on the resource attributes.
Table 10-1 Implications of the Low and High Values for the TE Tunnel Setup and Holding Priorities
High Value Low Value
Setup Priority Likely to preempt established TE
tunnels (preemptor).
Less likely to preempt established
TE tunnels (nonpreemptor).
Holding Priority Less likely to be preempted by a
newly established TE tunnel (non-
Likely to be preempted by a
newly established TE tunnel
Table 10-2 Policy on Including or Excluding a Link in a TE Tunnel Path Selection
Resource Class
Attribute of a Link Resource Class Affinity of a TE Tunnel
Policy on
Including or
Excluding the Link
in a Possible TE
Tunnel Path
Resource Class
Mask Resource Affinity
1 1 1 Explicit inclusion
0 1 0 Explicit exclusion
1 or 0 0 0 Don’t care

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