Now in networking devices specifically with quality of service we have the concept of trust and a trust
boundary.
Who are you going to trust.
So as an example if a switch receives a data packet from a P.C. is it going to trust the markings.
If the piece is telling the switch that its traffic is very important.
Typically a switch will not trust a P.C. but a switch made trust to the markings from a phone an IP
phone as an example will tell a switch by using a marking that its traffic is very important.
A switch needs to be configured to trust that marking from the phone.
So we have this concept of a trust boundary an untrusted domain is the part of the network that you
are not managing.
So it could be a P.C. it could be a printer.
You're not going to trust the marking sent by a user's P.C. from a quality of service point of view.
The trusted domain is the part of the network that only administrators can manage.
So they are trusted devices such as routers and switches and in some cases IP phones.
A broad is going to trust the markings that it receives from a switch and a switch is going to trust
the markings that it receives from an IP phone.
Now the trust boundary is where packets are classified and marked.
So as an example the IP phones are a trust boundary.
We don't trust the markings to the left of the IP phones but we do trust the marking centre between
phones switches and routers so in an enterprise any markings received by any of these devices will be
trusted.
A service provider or ISP however may not trust the mocking sent on packets from customers.
So this would be a separate trust boundary.
The ISP will trust any markings of packets in its own domain or in its own network that may not trust
the markings sent to it by a enterprise customer in an enterprise network.
The trust boundaries typically the edge of the network for an ISP the trust boundaries typically found
at the Lost device that it manages.
So as an example if the ISP provide you a router that it manages the trust boundary is set there and
it will trust any markings of devices that it controls but not markings received from devices that it
doesn't control.
Trust boundaries are important because by default Cisco riders will override any quality of service
markings that they receive on an untrusted boundary.
So foist traffic and video traffic and data traffic will be treated to the same.
If you don't remark that traffic in other words if a rider receives traffic on an untrusted interface
it will treat it the same which can have a negative effect on quality of service.