h to the grandmaster. This is especially helpful in ring to- pologies, and during failure events and network rearrangements. See section 6.3.1, "Alternate BMCA," and Annex B of G.8275.1 for further details. Remember that a T-GM only has ports in master state (they cannot be slave) and T-TSC ordinary clocks can only have PTP ports in slave state. Requires a physical form of frequency (normally SyncE) in combination with PTP. This is com- monly referred to as "hybrid mode" because it is a hybrid of packet and physical methods. One-step and two-step clocks are both allowed, with the master free to use whatever method it prefers, and the slave required to accept either. Required to use the two-way method, as this is needed to recover phase. Delay_Re and Delay_Resp messages are used, but the Pdelay message set is not used, SO there are no P2P TCs allowed in this profile. Quality (clockClass) values have specific values within the range of 6-255 (depending on the clock type). When operating normally, a value of 6 is expected across the network. Local priority can be configured on each PTP port of a clock to act as a tiebreaker in the case where multiple paths to a grandmaster are available. This is used where the operator wishes to define a preferred path. Fixes the value of priority1 at 128 but allows the value of priority2 to be configured in the range of 0-255 for T-GM and T-BC clocks (default of 128) and fixed at 255 in T-TSC clocks. The aB- MCA selects a port receiving the higher priority2 (lower value) to be the slave to a grandmaster if the clock quality is otherwise equal. Appendix IV of G.8275.1 describes possible use cases for the priority2 attribute. G.8275.1 is very easy to configure and deploy-do not let the reference to multicast put you off. For Cisco routers running IOS-XR, PTP and SyncE are enabled on the physical interface with a few lines of configuration and that is all that needs to be done. The PTP messages are sent out that inter- face to the multicast MAC address. When the interface at the other