One of the new topics on the revised Cisco Certified Network Associate 200-120 and Cisco Certified Entry Networking technician 100-101 exam is Rapid Spanning Tree Protocol. This is an enhancement to Spanning Tree Protocol as the world of networking technologies continue to evolve. So for most CCNA candidates STP was difficult and confusing enough. Now Cisco has made the exam that much harder in that you have to completely understand RSTP too. As I have been playing around with some of the Juniper routers and switches to possibly take the Junos JNCIA certification exam, one of the things that I noticed is how much easier the Juniper exams seems to be compared to the Cisco CCNA exam. The Junos certification track and especially the JNCIA exam compared to the Cisco CCNA exam seems to cover only about half the amount of material and it does not seem to be as scenario based (which means more difficult) as the Cisco exams.
But anyway, I got a little off track there. So back to our CCNA exam question on RSTP. We will start you off with a pretty easy question setting our foundation for Rapid Spanning Tree Protocol as it is purely theory based as you don’t have to dissect a switch topology. So this should be super easy!
Which three characteristics are associated with Rapid Spanning Tree Protocol? (Choose three)
A. RSTP uses the same timer-based process as STP on point-to-point links.
B. RSTP significantly reduces topology reconvening time after a link failure.
C. Forward delay and max age timers are unneeded
D. Lacks backward compatibility with IEEE 802.1D
E. Compatible with rapid PVST+
F. RSTP expands the STP port roles by adding the alternate and backup roles.
Topic & Question Explation: STP, RSTP, PVST+
RSTP provides faster spanning-tree convergence after a topology change which is answer B. RSTP implements the Cisco-proprietary STP extensions, BackboneFast, UplinkFast, and PortFast, into the public standard. As of 2004, the IEEE has incorporated RSTP into 802.1D which contradicts answer D.
C is right because RSTP is able to actively confirm that a port can safely transition to the forwarding state without having to rely on any timer configuration.
RSTP is not compatible with PVST+ since PVST+ is CISCO proprietary while RSTP is an IEEE standard, therefore E is wrong.
The RSTP port roles are designated, root, alternate and backup which means F is correct.
So the correct answers are B, C and F.
The best way to see this in real life is to have a CCNA home lab with three switches like a Cisco 2950, Cisco 2960, Cisco 3550 or Cisco 3560 switch. This way you can create your own topology and see how reconvergence and the port roles work.
I might suggest that you review the following protocols to fully understand how all the Spanning Trees work.
Now to put this into action, you can build your own CCNA switching lab.
If you do not have your own lab, you can look at some of our options here.