MCP Best practices ?

[suneq]

Hi,

I'm checking the ACI design guide (https://www.cisco.com/c/en/us/td/docs/dcn/whitepapers/cisco-application-centric-infrastructure-design-guide.html) after a year not touching ACI and found that the MCP best practices changed a bit. I remembered that MCP per-VLAN was recommended on all types of interfaces - as indicated here : https://www.cisco.com/c/dam/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/aci-guide-using-mcp-mis-cabling-protocol.pdf but now the best practices in the design guide are:

- enable MCP selectively on the ports where MCP is most useful, such as the ports connecting to external switches or similar devices if there is a possibility that they may introduce loops >>> this is not really clear to me cause every misconfigured server could potentially introduce loops, right?

- enable per-VLAN MCP with caution

Could you please share your experience with MCP? Have you enabled it per-VLAN or not? on all interfaces or only on interfaces connecting to external switches? Many thanks.

[RedNectar · Accepted solution]

Hi @suneq ,

I'm checking the ACI design guide (https://www.cisco.com/c/en/us/td/docs/dcn/whitepapers/cisco-application-centric-infrastructure-design-guide.html) after a year not touching ACI and found that the MCP best practices changed a bit. I remembered that MCP per-VLAN was recommended on all types of interfaces - as indicated here : https://www.cisco.com/c/dam/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/aci-guide-using-mcp-mis-cabling-protocol.pdf 

Your interpretation of this guide is different to mine. I don't see ANY recommendation in that doc - it just tells you how it works

but now the best practices in the design guide are:

- enable MCP selectively on the ports where MCP is most useful, such as the ports connecting to external switches or similar devices if there is a possibility that they may introduce loops >>> this is not really clear to me cause every misconfigured server could potentially introduce loops, right?

No. Misconfigured servers will not introduce loops UNLESS that server is say running a simulated switch that is misconfigured - such as a GNS3 simulated switch.

- enable per-VLAN MCP with caution

The reason for this is explained here: https://www.cisco.com/c/en/us/td/docs/dcn/aci/apic/6x/verified-scalability/cisco-aci-verified-scalability-guide-601.html

 Per-leaf scale for MCP:

256 VLANs per interface

2000 logical ports (port x VLAN) per leaf

Could you please share your experience with MCP? Have you enabled it per-VLAN or not? on all interfaces or only on interfaces connecting to external switches? Many thanks.

---

My experience has been in the lab only, but the point of MCP is that it is only needed when something else is broken somewhere else!  So it should NEVER be needed. In theory!

[luizlalmeida]

Hi,

The statement "... but the point of MCP is that it is only needed when something else is broken somewhere else!  So it should NEVER be needed. In theory!" only works in, as you said, a perfect world where nobody makes mistakes and nothing breaks. Protocols like MCP exist exactly to protect against human mistakes and equipment failures such as backdoor "forgotten" cables, malfuncioning HW or SW, etc. It´s like configuring Port Fast in the belief that noboby will ever connect a switch to that port, but it may (and Murphy guarantees it will) happen one day and break your L2 network, so add a BPDU guard to that port too!!

That´s why the name is "Best" Practices. You´re not required to configure, but you´d better do it!! It may save you from a visit to the HR department.

Luiz

[suneq]

Hi @RedNectar , thanks for your reply. I learned a lot from your blogs, keep up the good work.