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Extreme Certified Professional - Extreme Switching study materials
Extreme Certified Professional - Extreme Switching study resources

Extreme Certified Professional - Extreme Switching: VLANs, Spanning Tree, and Layer 2 Redundancy

Extreme Certified Professional - Extreme Switching · Work through your exam, one topic at a time.

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VLANs, Spanning Tree, and Layer 2 Redundancy

Domain 3 - VLANs, Spanning Tree, and Layer 2 Redundancy. This domain tests VLAN membership rules (tagged versus untagged), how to configure STP/RSTP/MSTP on ExtremeXOS, and when a ring or multi-chassis technology is the better answer than spanning tree.

VLAN rules

  • create vlan Sales tag 100 creates a named VLAN with an 802.1Q tag; the default VLAN is Default with tag 1.
  • configure vlan Sales add ports 1:1-1:8 untagged and configure vlan Sales add ports 2:1 tagged.
  • A port can be untagged in exactly one VLAN but tagged in many. A tagged/untagged mismatch between two switches is the classic "link up, no traffic" fault.
  • Verify with show vlan, show vlan <name>, and show fdb for learned MACs per VLAN.

Spanning tree

  • ExtremeXOS groups STP configuration into STPDs; the default is s0. Modes are set with configure stpd s0 mode dot1w for RSTP, dot1d for 802.1D, or mstp for 802.1s.
  • Bind VLANs with configure vlan Sales add stpd s0, then enable stpd s0 and enable stpd s0 ports 1:1-1:8. Enabling the STPD does not enable it on ports.
  • Root election uses the lowest bridge ID (priority, then MAC); lower priority wins, so core switches should be set below the 32768 default.
  • Edge protection: configure stpd s0 ports 1:5 edge-safeguard bpdu-restrict disables an access port that receives a BPDU instead of letting it become a root path.
  • MSTP maps VLANs to instances; region name, revision and VLAN-to-instance mapping must match on every member or separate regions form.

Alternatives to STP

EAPS and ERPS converge faster than STP and scale across many VLANs; a master node blocks one ring port for protected VLANs while still forwarding control traffic. MLAG dual-homes a server or switch to two peers without a blocked link.

Worked example

Two access switches uplink to a core pair. VLAN 10 should prefer core A and VLAN 20 should prefer core B. A single spanning tree instance cannot do this: both VLANs follow one topology. Put all switches in one MSTP region with VLAN 10 mapped to instance 1 and VLAN 20 to instance 2, then make core A the instance 1 root and core B the instance 2 root. Verify with show stpd and confirm region name and revision match on all three switches.

Traps

  • Forgetting enable stpd ports, or applying edge-safeguard/bpdu-restrict to an uplink and cutting the topology.
  • Mismatched MSTP region parameters, producing two regions and an unexpected root.
  • Expecting a ring to converge without enabling EAPS/ERPS on every node.