DualHoming 2248TP-E to N7K's?

[pmajumder]

Hi,

What are the pros and cons of Dual-Homing Fex's to N7K ruunning in vPC mode. Will dual-homing allow vPC connectivity for hosts such as servers?

Thanks,

Pradeep                

[Leo Laohoo · Accepted solution]

What are the pros and cons of Dual-Homing Fex's to N7K running in vPC mode.

Is this dual-/multi-homing a Nexus 2K to a single N7K or a dual N7K in a vPC?

If this is to a single N7K, it's OK but, in my opinion, as a last resort.  If it's to a pair of N7K in a vPC, then I don't recommend it. 

Why not?  Because if you dual-/multi-home a Nexus 2K to a pair of vPC N7K, and you ran into a rare event of Split Brain then you'll risk getting turmoil with your downstream clients.  I know that this design is a favorite among architects and designers but in the wild, it's currently not recommended.   The proven "best practice" is to dual-/multi-home the Nexus 2K to a single chassis.

In regards about my first statement as being a "last resort".  The reason why I'm saying that is because of the cost of a single Nexus 7.  What if you have hit the limit of the number of N2K the N7K can support?  If you want very high speed (10- or 40 Gbps) uplinks, then consider terminating your N2248PQ to N6K and your N6K can go up to the N7K via 40 Gbps (using N7K-M206FQ-23L).

.

[pmajumder]

Thank you!

[Steve Fuller · Accepted solution]

Hi Pradeep,

I can't find any links to documents that specifically state this, but dual-homed FEX on the Nexus 7000 is not supported at this time.

The supported topologies for FEX connectivity to the Nexus 7000 can be seen in the forum document Nexus 7000 Fex Supported/Not Supported Topologies although to be clear this only shows for releases up to NX-OS 6.0.

Additionally there have been a number of discussions with recent responses stating this.

Nexus 7000 & Fex - Port-Channel problem

01-Feb-2013 03:36 (in response to vldmegafondv)

Nexus 7000 & Fex - Port-Channel problem

1 FEX to 2 parent 7Ks is not supported at this time with the current software releases

Nexus 7000 NX-OS 6.1 Fex active active

03-Oct-2012 01:54 (in response to prasad.gsmc)

Nexus 7000 NX-OS 6.1 Fex active active

Dual homed FEX is not supported with Nexus 7000 at this time.

The view is that when connecting FEX to the Nexus 7000, dual-homing does not add any level of resilience to the design. A server with dual NIC can attach to two FEX  so there is no need to connect the FEX to two parent switches. A server with only a single NIC can only attach to a single FEX, but given that FEX is supported by a fully redundant Nexus 7000 i.e., SE, fabrics, power, I/O modules etc., the availability is limited by the single FEX and so dual-homing does not increase availability.

Regards

[Leo Laohoo]

Nah, you're right, Steve.  Dual home to a N7K is not supported.  I'm just getting mixed up with N5K.

[pmajumder]

Thank you also!