CCNA 200-301 v1.1 reference — Network Access

Rapid PVST+

Root bridge election, port roles and states, path cost and tie-breaking, and how Rapid PVST+ converges faster than classic STP.

Objective 2.5v1.1 exam target

Quick Reference Handbook

Root election and roles

Spanning Tree prevents Layer 2 loops by blocking redundant paths while keeping one active tree. Rapid PVST+ is Cisco's per-VLAN implementation of 802.1w RSTP: each VLAN computes its own topology and reconverges in sub-second to a few seconds instead of classic STP's ~50 seconds.

Election sequence

Every switch advertises its Bridge ID: priority (lower wins; default 32768) + system ID extension (VLAN) + MAC (tiebreak).
The lowest BID becomes the root bridge for that VLAN.
Each non-root switch picks its root port — the port with the lowest cost path to the root.
Each segment picks one designated port (the port advertising the best path); everything else becomes alternate/backup and discards.

RSTP port roles and states

Role	State	Meaning
Root port	Forwarding	Best path to the root on each non-root switch
Designated port	Forwarding	Best port for a segment — forwards for that link
Alternate port	Discarding	Backup path to the root (blocked)
Backup port	Discarding	Backup for a designated port on a shared segment

Pick the root and root ports

SW1: BID 24586 + VLAN10, MAC aaaa.bbbb.0001
SW2: BID 32778 (default 32768+VLAN10), MAC bbbb

Compare priority: SW1 24586 vs SW2 32778 → SW1 lower → SW1 is root.
On SW2 the port with the lowest root path cost to SW1 becomes the root port.
On the shared segment, SW1's side advertises the better path → SW1's port is designated and forwards; SW2's redundant port goes alternate/blocking.

Lower BID wins the root; closer-to-root wins the forwarding roles.

Port states and timers

STP/RSTP timers and parameters

Defaults are per standard and Cisco implementation; verify platform docs for exact values.
Parameter	Classic STP (802.1D)	Rapid PVST+ (802.1w)
Hello interval	2 s	2 s
Max age	20 s	3 missed hellos (~6 s) triggers reconvergence
Learning states	Listening 15 s + Learning 15 s	Discarding → learning → forwarding, often sub-second with edge ports
Convergence	~30–50 s	Sub-second on point-to-point links via proposal/agreement
Port cost (default)	Bandwidth-derived (e.g., 1G = 4)	Same cost model

Defaults are per standard and Cisco implementation; verify platform docs for exact values.

$ show spanning-tree vlan 10 (interpreted)

VLAN0010 Root ID Priority 32778 Address 00aa.bb01.0201Root's BID — priority 32768+VLAN10.

Root port Fa0/1Non-root switch: its best path to the root leaves Fa0/1.

Gi1/0/1 Desg FWD 4 128.1 P2pDesignated port forwarding, cost 4, point-to-point link.

Gi1/0/2 Root FWD 4 128.2 P2pRoot port — best path toward the root.

Gi1/0/3 Altn BLK 4 128.3 P2pAlternate port blocked — your redundant path.

Verification and control

Verify and influence STP

Confirm topology and optionally set a primary root — Privileged EXEC (+ global config for priority)

Cisco IOS / IOS XE

configure terminal
spanning-tree vlan 10 root primary
 end

Verify

show spanning-tree
show spanning-tree vlan 10
show spanning-tree root

The intended root shows no root port; non-root switches each show one root port.
Blocked ports sit on the side you expect — redundancy exists but doesn't loop.

root primary lowers priority toward 24576 — don't leave elections to chance with default priorities.

Changes device configuration.

Common mistakes

Assuming blocking means a failed link — blocking IS the healthy redundant state.
Believing RSTP changes the election — the algorithm is the same, only convergence is faster.
Expecting STP to preempt at root-election rate — a superior BID triggers re-election, but convergence timing depends on timers and topology, not a fixed deadline.
Forgetting STP runs per-VLAN — different VLANs can legitimately have different roots and topologies.
Tuning priority without planning — root placement determines which links forward.

Unplanned topology after adding a switch

Observation: A new switch becomes root and half the uplinks now block on the wrong side.

Hypotheses

New switch has lower default BID than the intended root
Path costs differ from the design (slower links preferred or faster blocked)
PortFast incorrectly applied to an uplink

Check	Indicates
`show spanning-tree root` per VLAN	Identifies the actual root vs the intended root.
Port costs and link speeds on the new paths	Confirms cost-based role choices.
`show spanning-tree interface` detail for PortFast	PortFast on a switch link bypasses safety.

Correction: Set explicit primary/secondary root priorities and remove PortFast from uplinks.

Root placement matches the design and blocked ports sit on intended redundant links.

On this page

Root election and roles
Port states and timers
Verification and control

Related resources

Practise this topic Source topic 20: Spanning Tree Protocol (Part 1)Practise topic 20 deck Source topic 22: Rapid Spanning Tree Protocol (RSTP)Practise topic 22 deck

Sources

Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
IEEE 802.1 Working Group (802.1Q/802.1w) — reviewed 2026-11-02
Cisco — LAN Switching Command Reference — reviewed 2026-11-02

Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.