It common especially, some of the newer featured to not be configured no the switch. Use of IEEE 802.1D and not Rapid-STP is one such common examples which greatly affects the SNAC Implementations.
This article is the second steps in identifying/fixing performance/throughput issues on a switch after a SNAC deployment. The first step ofcouse is to configure the legacy STP (which is the fall-back/legacy support). For more details on/pertaining to STP, refer to another article below:
https://www.symantec.com/connect/articles/snac-lan-enforcement-switch-performancethroughput-dropped-after-enabling-8021x
The classic IEEE 802.1D protocol has the following default timers: 15 seconds for listening, 15 seconds for learning, 20 second max-age timeout. All switches in the spanning tree should agree on these timers and you are discouraged from modifying these timers. These older timers may have been adequate for networks 10 to 20 years ago, but today this 30 to 50 seconds of convergence time is far too slow especially for SNAC implementations
Today, many switches are capable of Rapid Spanning Tree Protocol (IEEE 802.1w), but few network administrators have enabled it. RSTP vastly improves convergence times by using port roles, using a method of sending messages between bridges on designated ports, calculating alternate paths, and using faster timers. Therefore, organizations should use RSTP when they can. If your organization still has switches that cannot run RSTP, don't worry, the RSTP switches will fall back to traditional 802.1D operation for those interfaces that lead to legacy STP switches.
The 802.1D Spanning Tree Protocol (STP) standard was designed at a time when the recovery of connectivity after an outage within a minute or so was considered adequate performance. With the advent of Layer 3 switching in LAN environments, bridging now competes with routed solutions where protocols, such as Open Shortest Path First (OSPF) and Enhanced Interior Gateway Routing Protocol (EIGRP), are able to provide an alternate path in less time.
Cisco enhanced the original 802.1D specification with features such as Uplink Fast, Backbone Fast, and Port Fast to speed up the convergence time of a bridged network. The drawback is that these mechanisms are proprietary and need additional configuration.
Rapid Spanning Tree Protocol (RSTP; IEEE 802.1w) can be seen as an evolution of the 802.1D standard more than a revolution. The 802.1D terminology remains primarily the same. Most parameters have been left unchanged so users familiar with 802.1D can rapidly configure the new protocol comfortably. In most cases, RSTP performs better than proprietary extensions of Cisco without any additional configuration. 802.1w can also revert back to 802.1D in order to interoperate with legacy bridges on a per-port basis. This drops the benefits it introduces.
Ref:http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24062-146.html