CCNP DC · FABRICPATH EDGE

Nexus: FabricPath edge toward classic Ethernet

SW3 is a classic Ethernet switch with one uplink to each leaf. The FabricPath edge switches act as one spanning-tree bridge (c84c.75fa.6000) toward it, but SW3 currently has the better bridge ID, so the leaves block their edge ports and PC3 is cut off. Make the fabric the root.

CCNP Data Center track · Cisco Nexus (NX-OS-style) + Cisco · 4 objectives

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Objectives

The simulator ticks each one as soon as the network meets it.

On L1, show spanning-tree vlan 10: the edge port is blocked as L2 Gateway (Backbone) Inconsistent.
On L1 and L2 set spanning-tree pseudo-information, vlan 10 root priority 4096.
On SW3, show spanning-tree vlan 10: the root is c84c.75fa.6000 and exactly one uplink is blocked, because the fabric is one bridge.
Ping PC1 (192.168.10.10) from PC3.

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Before you start

Every FabricPath edge switch sends the same bridge ID, so a classic switch dual-homed to two leaves sees one root and blocks one uplink, like a loop to a single switch. The fabric must win the root election: a superior BPDU from classic Ethernet blocks the edge port instead.

Concept

FabricPath: routing Layer 2 frames between switch-ids

FabricPath replaces spanning tree inside the data-center core. Every switch has a switch-id, and FabricPath IS-IS computes shortest paths between switch-ids over all FabricPath links, so no core link is blocked and equal-cost paths are all used. Frames from classic Ethernet are encapsulated with the source and destination switch-id at the edge.

Concept

Spanning tree: one loop-free path

Redundant links between switches form a loop, and Ethernet frames have no TTL, so a broadcast would circle forever. Spanning tree elects a root bridge and blocks just enough ports to break every loop, while keeping the blocked link as a standby.