Category: Fabrics

Cisco Nexus 2000/7000 vPC Design Options

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

Cisco Nexus 2000/7000 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

 

Cisco Nexus 2000/7000 vPC Design

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 vPC32 with Sup1/2; 48 with Sup2E
Straight-through64 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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Ultra-low-latency ToR Switches For Building Scalable Leaf-Spine Fabrics

When building scalable Leaf-Spine fabrics, network architects look for low-latency, high-density switches to use at the leaf layer. There are many fixed switches that can be used for Top-0f-rack (ToR) at the leaf layer to provide connectivity upstream to the spine layer. What I’m about to compare are 3 ultra-low-latency ToR switches based on merchant silicon available in the market today for that purpose.

Cisco Nexus 3064 

The 3064 is 1 RU heigh and has a low latency and low power consumption per port. It has (48) 1/10GbE ports and (4) 40 GbE uplinks which can be each used in native 40 GbE or split into four 10GbE ports. It runs the same Nx-OS as the Nexus 7000 and 5000 series.

The Nexus 3064 is Cisco’s first switch in the Nexus family to use merchant silicon (Broadcom Trident+ chip). I’m curious to see whether Cisco will continue to use merchant silicon in future products or stick to their propreitery Nuova ASIC of the 7000 and 5000 series.

 

Arista 7050S-64

Arista 7050S-64 is very similar to the Cisco Nexus 3064 in terms of latency, interface types, and switching capacity. Its power consumption is less than the Nexus 3064 though. Arista’s fixed switches are known for their low power consumption and the 7050S-64 is no exception. Its power consumption is under 2W per port. You really cannot beat that!

 

Dell Force10 S4810

The Dell Force10 S4810 is another great ToR switch that can be used to build leaf-spine fabrics. It offers the same interface types as the Nexus 3064 and Arista 7050s-64; and similar form factor. It does however have slightly higher power consumption per port.

 

Ultra-low-latency 10/40 GbE Top-of-Rack Switches

Cisco Nexus 3064Arista 7050S-64Dell Force10 S4810
Ports48 x 1/10GbE SPF+ and 4 x 40GbE QSFP+48 x 1/10GbE SPF+ and 4 x 40GbE QSFP+48 x 1/10GbE SPF+ and 4 x 40GbE QSFP+
Packet Latency (64 bytes)824ns800ns700ns
OSNx-OSArista EOSFTOS
Form Factor1 RU1 RU1 RU
Switching Capacity1.28 Tbps1.28 Tbps1.28 Tbps
Power Supply2 Redundant & Hot swappable power supplies2 Redundant & Hot swappable power supplies2 Redundant & Hot swappable power supplies
Typical Operating Power177W103W220W
Full Data SheetData SheetData SheetData Sheet


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Cisco Nexus 2000/5000 vPC Design Options

Virtual PortChannel (vPC) allows two links that are connected to two different physical Cisco Nexus 5000 or 7000 switches to appear to the downstream device as a single PortChannel link.  That downstream device could be a server, Nexus 2000, or any Classical Ethernet switch.

vPC is useful to prevent spanning tree from blocking redundant links in the topology. After all you  have spent fortune and bought those expensive 10G ports and the last thing you want is for spanning tree to block them.

Having said that they are several ways to connect the Cisco Nexus Fabric Extender (FEX) to its parent the Nexus 5000 or 7000 switch. In this post I’m going to discuss supported vPC topologies for the Nexus series. I’m going to start with the Nexus 2000/5000 now and will add a separate post for the Nexus 2000/7000 options later.

 

Without vPC

Cisco Nexus 2000/5000 Without VPC

The picture above shows the supported non-vPC topologies. Topology A on the left shows a straight forward connectivity between Nexus 2000 and 5000 with a server connected to a server port on the Nexus 2000. There is no redundancy in this topology and failure of the Nexus 5000 or 2000 would cause the server to lose connectivity to the fabric. In this design you can have up to 24 FEX’s per Nexus 5500 in L2 mode and 16 FEX’s in L3.

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 24 FEX’s per Nexus 5500 in L2 mode and 16 FEX’s in L3.

 

With vPC

Cisco Nexus 2000/5000 VPC

The picture above hows the supported vPC topologies for the Nexus 5000. Topology C is called straight-through vPC in which each Nexus 2000 (FEX) is connected to one parent Nexus 5000 while server is dual-homed. 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 48 FEX’s (24 per Nexus 5500) in L2 mode and 32 FEX’s (16 per Nexus 5500) in L3 mode.

In topology D on the other hand each FEX is dual-homed and so is the server. So the NIC on the server must support LACP as in C. In this topology you can have up to 24 FEX’s in L2 mode and 16 FEX’s in L3.

Topology E is similar to D where each FEX is dual-homed but the server is single-homed. In this topology you can have up to 24 FEX’s in L2 mode and 16 FEX’s in L3.

 

Maximum Supported Cisco FEX As of Today:

Nexus 5000Nexus 5500
Without vPC (L2 Mode)1224
Without vPC (L3 Mode)X16
Straight-through (L2 Mode)24 (12 per Nexus 5000)48 (24 per Nexus 5500)
Straight-through (L3 Mode)X32 (16 per Nexus 5500)
Dual-homed FEX (L2 Mode)1224
Dual-homed FEX (L3 Mode)x16

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