Stage 2 · Lesson 5 of 8
Spanning tree
Redundant links between are good for resilience but create loops, and frames have no hop limit, so a loop floods the network with copies of until it stops working, a . prevents this.
The switches elect a root bridge (lowest bridge ID), every other switch picks its best path towards it (the root port), and redundant ports are put into a blocking or alternate role. If a link fails, a blocked port takes over. Cisco runs Rapid PVST+, which builds one fast-converging tree per VLAN.
Always choose the root yourself with spanning-tree vlan X root primary, on a core or distribution switch.
Common trapletting the election happen by chance, so an old switch in a cupboard becomes root and carries all the traffic.
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Resources for this stage
Start with· follow one of these
- VideoFreeJeremy's IT Lab: CCNA 200-301 Complete Course
Jeremy's IT Lab · Beginner
The VLAN, spanning tree and EtherChannel days, each with a Packet Tracer lab to do straight after
- PlatformFreeCisco Networking Academy
Cisco · Beginner
The switching and VLAN modules of the CCNA courses, if your university or institute runs them