DCII: Configuring Fabric Extenders

Cisco Nexus 2000 FEX Overview:
• FEX = fabric extender (aka port extender)
• extends ports by acting as a remote line card for a Nexus switch
• physical: host➖FEX➖Nexus
• logical: host➖Nexus
• all management on parent switch; no console/vty access on FEX

Traffic flow steps:
1️⃣ FEX finds the parent switch (through the upstream port).
2️⃣ FEX informs parent switch of the number of ports it has.
3️⃣ The switch creates logical interfaces for each FEX port.
4️⃣ FEX tags packets with a VNTag that the controlling switch assigns.

FEX Deployment Models:
• straight-through FEX using static pinning
• straight-through FEX using dynamic pinning (uses port channels)
• active/active FEX using vPC
• different Cisco Nexus platforms do not support all deployment models

FEX with Static Pinning:
• pin the server ports on FEX to one of the uplink ports
• example: if there are 48 FEX server ports and 4 uplinks, 12 server ports need to pin to each uplink
• when an uplink port fails, all downlink ports pinned to it are disabled

FEX with Dynamic Pinning:
• all server ports share the combined bandwidth of the uplink ports ➡️ configure a port channel between FEX and Nexus
• traffic is distributed based on the load balancing hashing algorithm
• server downlinks are not disabled if an uplink fails

Active/Active FEX:
• FEX dual-homed to two Nexus switches
• highest availability in FEX-based solutions
• vPC as a FEX uplink connection (dynamic pinning)
• identical FEX configuration on both parent switches (automatic configuration synchronization also available)

Enhanced vPC Overview:
• enhanced vPC = two-layer vPC
• all paths from hosts to FEXs and then to switches are active
• combination of two supported vPC topologies: dual-homed connection of a host to FEXs and dual-homed connection of a FEX to two switches