vPC Design Variations

Virtual Port Channel Series: 

Today we are going to discuss different design types in which vPC can be implemented:

1. Host vPC
2. Fabric vPC
3. Enhanced vPC
4. Back to Back vPC
5. vPC+
6. Anycast vPC

• Host vPC: Host vPC is a simplest design where Nexus vPC switches are directly connected to host device.

• Fabric vPC: In this vPC design, the Nexus switches are connected to host via Fabric Extenders (FEX).

       

• Enhanced vPC: This is the enhancement to Fabric vPC where vPC is extended till hosts connected to FEX so both the FEX are behaving as Active/Active. With Enhance we have two options:

• Single-homed FEX topology where hosts are multihomed to FEX but FEX are in turn single homed to Parent Nexus switches.

• Dual-home FEX topology where both the FEX and hosts are dual homed.

• Back to Back vPC: A back-to-back vPC is a way of connecting two pairs of Nexus switches with vPC. Depending on the documentation, it is also known as Multi-Layer vPC or Double-Sided vPC. With this design, both ends think they have a connection to single switch. So logically, it’s a port channel between two switches. We will demonstrate Back to Back vPC in next Section.

• vPC+ : vPC when configured alongwith Fabricpath is known as vPC+. It enables both vPC switches to be represented as a single unique virtual switch to the rest of the Fabricpath enabled network. This is done by assigning a same switch id to both switches.

• Anycast vPC: vPC with VXLAN is referred to as Anycast vPC. The term anycast comes from the fact that same secondary loopback IP address is used on both switches to identify them as a single switch to the VXLAN network. We will discuss more about this in VXLAN configuration post.

Back to Back vPC Configuration and Verification:

1. Configured Peer link on the Port channel12 between Spine-1 and Spine-2.
2. Before configuring member ports, lets verify some features.

• Under normal conditions , one link between Spines and Leaf will be in Forwarding and all the other three links will be in blocking as per traditional STP.

• Lets ping SVI (10.0.0.13) on Spine-1 and SVI (10.0.0.14) on Spine-2.

• Verify the mac address table on Leaf. It is learned via only one designated port E1/3.

3. Configure Member ports on Spine towards Leaf and on Leaf towards Spine.

4. Now the Spine’s MAC will be learned over vPC Member port Po57.

5. All the 4 links will now be used for forwarding.

6. The twist here is that Secondary vPC Spine will have two Root ports
   1. One Root port towards Primary vPC over Peer link.
   2. Second Root port towards Leaf vPC Member Port.

With this, we have covered all the topics under vPC series. In case you want any other topic to be covered as well, please do write to us or comment below