IP Quality of Service

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.

Bandwidth

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

where

& 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-

preemptable).

Likely to be preempted by a

newly established TE tunnel

(preemptable).

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