2.1.i Describe spanning-tree concepts

2.1.i [i] Compatibility between MST and RSTP

Both RSTP and MSTP improve the operation of the spanning tree while maintaining backward compatibility with equipment that is based on the (original) 802.1D spanning tree, with existing Cisco per-VLAN spanning tree (PVST), and with the existing Cisco-proprietary Multiple Instance STP (MISTP). By default, RSTP uses topology change TC flag. It also doesn’t use separate TCN BPDU when interoperating with another switching running 802.1D.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1915-1918).  . Kindle Edition.

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3550/software/release/12-1_13_ea1/configuration/guide/3550scg/swmstp.pdf