CCNP DC · vPC

Nexus: vPC peer-switch, one spanning-tree root

The vPC pair works, but each peer is still its own spanning-tree bridge: whichever wins is the root, and if it fails SW3 has to elect a new one. With peer-switch both peers send the same bridge ID, so the pair itself is the root and losing a peer changes nothing for spanning tree.

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.

Give N1 and N2 the same priority for VLAN 10: spanning-tree vlan 10 priority 4096.
Enable peer-switch in vpc domain 10 on both peers.
On SW3, show spanning-tree vlan 10: the root address is the vPC system MAC 0023.04ee.be0a (peer-switch operational on both peers).
Ping PC2 (192.168.10.20) from PC1.

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Before you start

peer-switch makes both peers send BPDUs with the vPC system MAC (0023.04ee.be + the domain ID in hex) as their bridge ID. Both must use the same spanning-tree priority; with different priorities RouteCraft keeps peer-switch non-operational, as show spanning-tree summary tells you.

Concept

vPC pairing rules: keepalive VRF, type-1 checks, peer-switch, peer-gateway

Two Nexus switches become vPC peers only when they agree: the same domain ID, a trunk peer-link that is up, and a peer-keepalive they have both heard. The keepalive runs in VRF management (mgmt0) unless told otherwise. Once paired, global and per-vPC type-1 parameters must match, or vPCs are suspended. peer-switch and peer-gateway make the pair behave as one switch for spanning tree and for routing.

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.