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Now in networking devices specifically with quality of service we have the concept of trust and a trust

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boundary.

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Who are you going to trust.

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So as an example if a switch receives a data packet from a P.C. is it going to trust the markings.

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If the piece is telling the switch that its traffic is very important.

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Typically a switch will not trust a P.C. but a switch made trust to the markings from a phone an IP

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phone as an example will tell a switch by using a marking that its traffic is very important.

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A switch needs to be configured to trust that marking from the phone.

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So we have this concept of a trust boundary an untrusted domain is the part of the network that you

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are not managing.

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So it could be a P.C. it could be a printer.

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You're not going to trust the marking sent by a user's P.C. from a quality of service point of view.

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The trusted domain is the part of the network that only administrators can manage.

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So they are trusted devices such as routers and switches and in some cases IP phones.

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A broad is going to trust the markings that it receives from a switch and a switch is going to trust

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the markings that it receives from an IP phone.

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Now the trust boundary is where packets are classified and marked.

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So as an example the IP phones are a trust boundary.

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We don't trust the markings to the left of the IP phones but we do trust the marking centre between

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phones switches and routers so in an enterprise any markings received by any of these devices will be

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trusted.

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A service provider or ISP however may not trust the mocking sent on packets from customers.

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So this would be a separate trust boundary.

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The ISP will trust any markings of packets in its own domain or in its own network that may not trust

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the markings sent to it by a enterprise customer in an enterprise network.

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The trust boundaries typically the edge of the network for an ISP the trust boundaries typically found

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at the Lost device that it manages.

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So as an example if the ISP provide you a router that it manages the trust boundary is set there and

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it will trust any markings of devices that it controls but not markings received from devices that it

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doesn't control.

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Trust boundaries are important because by default Cisco riders will override any quality of service

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markings that they receive on an untrusted boundary.

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So foist traffic and video traffic and data traffic will be treated to the same.

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If you don't remark that traffic in other words if a rider receives traffic on an untrusted interface

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it will treat it the same which can have a negative effect on quality of service.