FEX to Nexus parent switch communication details

[ryanwalz]

I would like to know about FEX communication with the parent Nexus switch in a bit more detail.  I know the FEX is assigned an IP from 127.0.0.0/8 segment... but how is this actually used?  Is communication with the FEX itself encapsulated in the VN tag and the FEX determines somehow that the packet is destined for it instead of an interface?  Is there a way to see what IP the FEX has?  Is there a way to see ports the FEX is using on its IP address?

[Muthurajeshwaran Natesan]

Hi

The FEX IP address is 127.15.1.<fex-id>. In this example, FEX is 101:

Eg :Fex ip address will be:127.15.1.101

The Fabric Extender Operation

• HIF (Host Interface): Are the physical user/host interfaces on the FEX. These interfaces receive normal Ethernet traffic before it is encapsulated with the VN-Tag header. Each HIF interface is assigned a unique VN-Tag ID that is used with the encapsulation.
• NIF (Network Interface): Physical uplink interfaces on the FEX. These interfaces can only connect back to the parent switch and carries only VN-Tagged traffic.
• LIF (Logical Interface): Is the logical interface representation of the HIF and its configuration on the parent switch. Forwarding decisions are based on the LIF.
• VIF (Virtual Interface): Is a logical interface on the FEX. The parent switch assigns/pushes the config of a LIF to the VIF of an associated FEX which is mapped to a physical HIF. This is why replacing a FEX becomes trivial in that the broken FEX is unplugged and the replacement is plugged in.

Please let me know if your not able to understand.

Thanks,

Muthu.