established. A trust boundary is the point at which classification of traffic is either applied by the device
allowing traffic into the network or the device allowing traffic into the network trusts classification that
has been applied by the end station.
or IP Precedence in an environment where more granularity is required or where 802.1Q/p is not
available. It is desirable to have traffic classified by the signaling device itself and use trust as the traffic
enters the network, as is the case with Cisco IP phones and voice gateways. However, there are places
in the network where due to the need for administrative control or the lack of end station capabilities
classification or marking at the edge is required.
traffic. This section provides information about the following components:
(DSCP). The recommended configuration is to trust the L2 (CoS) classification applied by the phone on
the access port servicing the phone. This is accomplished through the application of the trust cos port
configuration option. Additionally, the IP phone must be configured to set the trust state of the "PC" port
on the IP phone. This is accomplished with the trust-ext interface/port level command. In most cases,
the IP phone's PC port should be set to an untrusted state where no classification of traffic by the PC is
allowed. Detailed examples are available in
CallManager can act as a conference bridge, in which case it generates VoIP Bearer traffic classified
with a DSCP value of EF. CallManager acting as a Music on Hold server also generates voice bearer
traffic marked with a DSCP value of EF. Additionally, a CallManager acting as a call setup agent in an
IP telephony network generates VoIP call control traffic (H.323, skinny station, and MGCP) all marked
with a DSCP value of AF31.
requirement of the network is that the trusted edge be configured to accept this classification. This is
accomplished through the use of the trust dscp or trust ip-precedence interface/port level configuration
command. Detailed examples by platform can be found in