When building data center networks using Cisco Nexus switches you can choose to attach the Nexus 2000 Fabric Extender (FEX) to a Nexus 5000 or 7000 depending on your design requirements and budget. In a previous post I briefly described the benefits of Virtual PortChannel (vPC) and discussed design options for the Nexus 2000/5500/5000. In this post I will go over the vPC design options for the Nexus 2000/7000 and important things to consider while creating the design.
Without vPC
The picture above shows how you can connect a Nexus 2000 to its parent switch Nexus 7000 without using vPC. Topology A on the left shows a single attached Nexus 2000 to a 7000 and a server connected to a server port on the Nexus 2000. There is no redundancy in this topology and failure of the Nexus 7000 or 2000 would cause the server to lose connectivity to the fabric. In this design you can have up to 32 FEX’s per Nexus 7000 with Sup1/2 or 48 FEX’s with Sup2E.
Topology B on the right has also no vPC and NIC teaming in this case is used for failover. The solid blue link is the primary connection and the dotted link is the backup. It’s up to the OS on the server to detect any failure upstream and fail over to the backup link. Similar to A in this design you can have up to 32 FEX’s per Nexus 7000 with Sup1/2 or 48 FEX’s with Sup2E.
With vPC
The picture above hows the supported vPC topology for the Nexus 7000. Topology C is called straight-through vPC in which each Nexus 2000 (FEX) is connected to one parent Nexus 7000 while the server is dual attached to a pair of Nexus 2000. In this case NIC on server must support LACP so that the two FEX’s appear as a single switch. Most modern Intel and HP NIC’s support LACP today. This topology supports up to 64 FEX’s (32 per Nexus 7000) with Sup1/2 or 96 FEX’s (48 per Nexus 7000) with Sup 2E.
Maximum Supported Nexus FEX As of Today:
| Nexus 7000 | |
|---|---|
| Without vPC | 32 with Sup1/2; 48 with Sup2E |
| Straight-through | 64 with Sup1/2 (32 per Nexus 7000); 96 with Sup2E (48 per Nexus 7000) |
Notes:
- The Nexus 7000 modules that support FEX are: N7K-M132XP-12L (32 x 10GbE SFP+), N7K-F248XP-25 (48 x 10GbE SFP/SPF+), and all M2 modules. The F1, F2 copper, and 1GbE M1 modules don’t support FEX
- All FEX uplinks must be placed in the same VDC on the Nexus 7000
- Dual attaching the FEX to pair of Nexus 7000 is not supported as of today on the Nexus 7000 which means in the event of I/O module failure all FEX’s hanging off of that module will be knocked out. For this reason it’s recommended to have at least two IO modules in the chassis that support FEX and distribute the uplinks across those two modules for redundancy
- If the FEX is going to be within 100 meters from the Nexus 7000, you can use Cisco Fabric Extended Transceiver (FET) on the uplinks which offers cost-effective way to connect the FEX to its parent switch. The FET is much cheaper than the 10G SFP+ optic
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