Cisco Nexus Fabric Extender: FEX 2000
FEX work like remote card for the parent Nexus switch. With FEX
we get logical ToR and physical EoR network topology. ToR provide better cable management
and EoR provide ease of device management.
There are three model of FEX
2100 series - 1st generation FEX
2200 series – 2nd generation FEx
2300 series – latest series.
Parent switch model ( Nexus 5K, 7K or 9K) will define the
FEX mode.
FEX deployment:
There are three method to deploy 2K FEX
- Straight – through FEX using static pinning ( server connected to FEX get dedicated uplink port from FEX to parent switch, if uplink fails server connection fails)
- Straight- through FEX using dynamic pinning (all uplink are bundled using ether channel, so end server connected to FEX will not be isolated until ether channels goes down.
- Active – Active FEX using vPC.
In straight – though connection there is direct connection from
FEX to Parent switch.
FEX is a dump device and is depended on parent switch for forwarding
traffic. VNTag is used between FEX and
parent switch.
Following are limitation of FEX
- No east / west switching, FEX require North / South traffic
- FEX cannot have downstream switches connected, it is intended for edge devices like Server / End nodes.
- As of now ( year 2016) PoE ports are not available on FEX.
- Dual homed FEX is supported only with Nexus 5K.
When frame passes via FEX, VNTag is added or removed from
the Frame. When FEX receives frame from edge devices connected to it, FEX added
VNTag (IEEE 802which helps parent switch
to make necessary forwarding decision or instruct FEX to forward frame to
appropriate device.
D : director bit ( d
= 0 if traffic is flow from host to
network; d = 1 if traffic flow is from network to host)
P: pointer bit ( set for multicast frame and requires egress
replication
L : Loop filter ( if frame is sent back to source FEX)
V : virtual interface ( interface or port on 2K FEX)
