ACI Loop Prevention scenario

[nexus13213]

Hi,

I will move server farm from legacy network to ACI,  

I have concern about the loop, when migrating blade servers that have switches.

here the scenario:

1. I've moved vlan 10 (EPG A) to ACI, but there are still some servers that are on the N7K.

2. then plans to move vlan 20 (EPG B) to ACI, but the blade server has a brocade switch that also has connections to the N7K

3. will there be loops with topology like this?

please advise,

if anyone has good document about loop scenario and prevention in ACI, please share it to me.

Thanks

[Manuel Velasco]

First of all note that ACI doesn't run STP as it only forwards the BPDUs (see link below)

https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c07-732033.html#_Toc395143572

Now regarding your question, one scenario where this topology can cause endpoint flapping is if a single enpoint (MAC address) behind the brocade switch utilizes both links to send traffic towards the ACI leaf on the same vlan. In this scenario you will see the enpoint MAC moving between the two interfaces and if the movement is to fast it can disable BD learning. To prevent this, you need to make sure that every endpoint only send traffic using one uplink all the time.

Another scenario is if all 3 EPGs are using the same BD which mean that all 3 vlans would be allow on the same BD and a single endpoint MAC is used to send traffic on multiple vlans.  To prevent this scenenario you would want to separate each vlan to its own BD.

hope this helps.

[nexus13213]

Hi manuel,

thank u for your response,

I have checked the switch brocade configuration, both uplink send traffic vlan differently, and each EPG using different BD. so, is this scenario loops free ?

and other question, should I enable MCP on that link ?

[Manuel Velasco]

Yes, that configuration will prevent the endpoint flapping.  If you want to enable MCP, I would recommend to just enable it on the ports that you are interested. I would also recommend reading the information about loops in the link below.

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-x/aci-fundamentals/b_ACI-Fundamentals/b_ACI-Fundamentals_chapter_010010.html#concept_706016DC62404574B77A5A4B3AD3C905