Cisco Meraki MX250 - IP Conflicts

[Shadius]

Hi all,

I am receiving IP conflict alerts from the MX250 about our Domain Controller using NIC Teaming. It seems like the NIC ports are taking turns coming online. One port loses connection, the other comes online.

Is there any explanation of why this may be happening and how it can be resolved?

[ww]

I guess you are not using link aggregation/LACP?

What mode is teaming configured?

The dc is connected to a switch?

How are the switch ports configured?

[Shadius]

Hi @ww 

Correct. Currently LACP is not configured. I'm not too familiar with LACP, so bare with me. No ports are aggregated on the switches from what I can see.

Yes, the DC is connected to our MS350 switch and each switch port is configured as an access port. We have a three switch switch stack and the connections are split between Switch 2 and Switch 3.

I will have to check with our System Administrators about the mode of NIC Teaming, but it might be set to Switch Independent.

[PhilipDAth]

If you are not using NIC teaming, the server is probably responding to some requests using one NIC and some with the other NIC.

So the MX will see two different NICs using the same IP address.

In this case, it is expected behaviour so you should ignore those warnings.

[Shadius]

Thanks@PhilipDAth 

Is there a best practice for setting this up?

I believe we are using NIC Teaming.

[PhilipDAth]

If it is just a domain controller (so it has low bandwidth requirements), I'd be tempted to configure it for simple active/standby NIC.  Then the standby NIC will only be used if the primary fails.  This will work no matter what kind of switch you have.

Meraki simple config.  Tolerant to all sorts of misconfigurations.

If you have a managed switch (such as any Meraki MS) you can use LACP (as suggested by @ww ).  LACP can also spread clients across the NICs, and both NICs are active at the same time.  You'll need to configure this on your MS:

https://documentation.meraki.com/MS/Port_and_VLAN_Configuration/Switch_Ports#SwitchPorts-LinkAggrega... 

And on the server:

https://docs.microsoft.com/en-us/windows-server/networking/technologies/nic-teaming/nic-teaming-sett... 

The above link also shows how to configure a standby NIC.

[Shadius]

I spoke with our System Administrators at our Data Center. We're using NIC Teaming, but it's configured through Dell's Broadcom Advanced Control Suite 4.

Found this link: https://www.dell.com/support/kbdoc/en-us/000105133/how-to-set-up-nic-teaming-on-windows-server-using...

All of our sites are configured this way. The decision to make would be whether it's better to set up LACP at all of our sites. I'm not sure if there's a pros and cons of using Dell's Broadcom Advanced Control Suite 4.