RSTP needs backwards compatibility with STP switches. Thus Discarding state merges Disabled, Blocking, Listening into one. Ideally if running a complete RSTP topology then discarding becomes practically unneeded due to the explanation below.
In STP BPDU will only be sent from root bridge > down, therefore non-root bridges would only forward on BPDUs that are received from the root-bridge via their root port. Therefore topology change will mean a longer convergence time as the TCN has to be propagated to the root bridge first then from the root bridge out to all remaining bridges in the switching domain.
For STP Hello(2 secs), max age timer (10 x hello time, by default 20s), then 15s each for Listening and Learning. If no timers are touched for STP and you haven't enabled any add-on features like backbonefast or uplinkfast then you can be looking at ~50s for convergence time.
In RSTP all switches can send BPDUs every hello time period not just the root bridge, the BPDUs carry up to date information. This enables faster convergence as the switch that determines the failure can advise the rest of the switching domain(bridge) of the TCN(Topology Change Notification) immediately. As the failure detection time becomes 3 x hello timer. Therefore if the hello timers are left at the default of 2 secs, detection of a failure can happen within ~6 secs.
RSTP also has two additional port states:
Alternate port : Technically in discarding state but is allocated as a alternate best path to the root-bridge. If the current root port fails the alternate port will take over.
Backup port : This port is allocated as a redundant designated port. If there is already a designated port forwarding for that segment then this port will remain backup until it is needed. Technically this port is in discard state until needed.
One more point RSTP marks edge ports as ports connected to end devices (No BPDUs expected on this port). This enables STP 'portfast' features to ensure the host port comes up as quickly as possible to avoid dropping DHCP packets etc.
These are the main differences - Hope this helps.
Found the answer:
show spanning-tree interface INT detail
This command goes deeper than the regular "show spanning-tree" and displays the designated bridge as well as root bridge.
Best Answer
Trunk port is Cisco terminology and Cisco is one of the few vendors implementing Per VLAN Spanning Tree + (PVST+) which is the equivalent to 802.1D but with one spanning tree instance per VLAN. There is also Rapid Per VLAN Spanning Tree + (RPVST+) which is the equivalent of 802.1w but per VLAN. The plus means that STP is running over 802.1Q trunks as opposed to ISL.
On an access port, only one VLAN is allowed, hence only one instance of spanning tree will be running on the port and the Bridge Protocol Data Units (BPDUs) will be sent untagged. Normally access ports will connect to end devices and the port would be configured as an edge port to bypass listening and learning state and to not generate any Topology Change Notification (TCN) on link up/down. You could run an access port between switches as well but that is generally a waste because you will want to have several VLANs between the switches. So far everything is the same but Cisco runs PVST+/RPVST+ and other vendors run STP/RSTP.
On a trunk port (Cisco terminology) several VLANs will generally be allowed to traverse the trunk. On Cisco devices, every VLAN will in its own instance and different VLANs can be forwarding on blocking on the same physical port. On other vendors there will only be one instance running, even though several VLANs are traversing the trunk. This means that all VLANs most follow the same topology. It's not possible to any form of load sharing/traffic engineering.
Cisco devices will allow a different number of instances depending on what platform it is. Some will allow 32 instances, some 64 and some 128 and so on.
There is also the option of running Multiple Spanning Treee (MST) which does not do per VLAN Spanning Tree. Instead it groups VLANs together into instances which is more effective.
The advantage of PVST+/RPVST+ is that you can send VLANs on different paths and do traffic engineering. Also a change in one VLAN will not affect the others. The drawback is that it's less scalable if you have a lot of VLANs.
The reverse is true for STP/RSTP, it scales better but it does not offer load sharing and changes sourcing from one VLAN can affect the others.