Enterprise QoS Solution Reference Network Design Guide

QoS Design Overview
Access Edge Trust Models
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Enterprise QoS Solution Reference Network Design Guide
Chapter 2 Campus QoS Design
However, SCCP is by no means the only call signaling protocol used in IP telephony environments.
Cisco recommends including all relevant call signaling ports required for a given IPT environment in the
access lists that identify call signaling protocols. Firewalls protecting CallManagers should also allow
additional ports to provide the supplementary services that CallManagers provide or require.
This section includes the following topics:
Trusted Endpoints
Untrusted Endpoints
Conditionally-Trusted Endpoints
The primary function of access edge policies is to establish and enforce trust boundaries. A trust
boundary is the point within the network where markings such as CoS or DSCP begin to be accepted.
Previously-set markings are overridden as required at the trust boundary.
You should enforce trust boundaries as close to the endpoints as technically and administratively
possible as shown in Figure 2-3.
Figure 2-3 Establishing Trust Boundaries
1
2
3
Endpoints Access Distribution Core WAN Aggregators
Legend for Figure 2-3:
1. Optimal trust boundary: trusted endpoint
2. Optimal trust boundary: untrusted endpoint
3. Sub-optimal trust boundary
The definition of the trust boundary depends on the capabilities of the endpoints that are being connected
to the access edge of the LAN. The following are the three main categories of endpoints as they relate
to trust boundaries:
Trusted endpoints
Untrusted endpoints
Conditionally-trusted endpoints
Trust Boundary
1 Optimal Trust Boundary: 2 Optimal Trust Boundary: 3 Suboptimal Trust Boundary
Trusted Endpoint
Untrusted Endpoint
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