DCNM VxLAN: What Does "L2 VNI Route-Target Both Enable" Option Do?

[AJ Cruz]

When you create a VxLAN network in DCNM on the Advanced tab "L2 VNI Route-Target Both Enable" is available as a check box.

At first I thought this had to do with Asymmetric vs Symmetric IRB modes, but playing around with it I noticed with both options the L3 VNI SVI remains intact and to confirm I see this on a Cisco Live breakout session (LTRDCT-1224): "Cisco follows Symmetric IRB"

Furthermore, when I toggle this option on and off the only difference I see in the config is:

  evpn
    vni 30001 l2
      rd auto
      route-target import auto
      route-target export auto

vs

  evpn
    vni 30001 l2
      rd auto
      route-target both auto

Isn't the net effect of the two the same? Does anyone know what that flag does (or is supposed to do)?

Thanks!

[Ray D]

I have only ever seen route-target both auto not route-target import both auto as you have used here below.  

  evpn
    vni 30001 l2
      rd auto
      route-target import both auto

 Regardless route-target both auto is just an alias for enabling both commands via one method,

 that is route-target both auto just generates this config to auto export and import route-targets.

      route-target import auto
      route-target export auto

Under EVPN, this is for the import and export of Mac Prefixes, its a per mac-vrf prefix import/export policy,   specifying the auto option is only valid for iBGP , Manual RT's are required for EBGP and asymmetric VNI's.

Ray.

[AJ Cruz]

ya sorry that was a typo, fixed in the original post.

I guess my question is why does DCNM have that option, what's the intent because as you said, it's just a shortcut for enabling both as far as I'm aware?

[Ray D · Accepted solution]

Yes, You have to remember those values are based off of templates essentially in DCNM, When you go to deploy fabrics and networks it is primarily based off underlying template values that are preset. 

For example if you check the template library under the Control tab and search for network and edit the "Default_Network_Universal" one which is most likely the template you are using when you go to add networks then that template is based on pre-defined values for several components including evpn, In that template(at the very end) you will see there is an if, else statement based on whether you select the auto both or not for evpn, either way it just derives to the same result - as this is what the template defines that you are using. If someone cloned that template and build their own you could modify the route-targets to be manual or other if you wish. 

So to answer you question, in this instance it is just that DCNM is doing that based on pre-defined values in the templates. 

If you search for evpn_vni in the templates and edit either of those values you will also see why it is setting those - again based off of templates, 

Attached screenshots for your reference.

Hope that helps

Ray.