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
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
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
Attribute of a Link Resource Class Afﬁnity of a TE Tunnel
Excluding the Link
in a Possible TE
Mask Resource Afﬁnity
1 1 1 Explicit inclusion
0 1 0 Explicit exclusion
1 or 0 0 0 Don’t care