Nexus 9k vxlan to classic vlan domain question - what is the behaviour.

andgriffin · ‎05-18-2017

Guys

I have a question RE connecting a VXLAN fabric running eVPN to classical ethernet switches.

I have my fabric mapping vlan 123 to a vxlan - VTEPs are hosted on the 9ks – it is a network overlay only.

Hardware Nexus 93180 software - 7.0(3)I4(2)

I have a requirement to connect multiple classic vlan switches running STP via L2 trunks and to have connectivity to hosts in vlan 123.

The classic vlan switches are inter-connected.

The classic vlan switches are / will be up-linking to the same leaf switch.

I do not want to be running spanning tree on the fabric.

My fairly obvious concern therefore is that my fabric leaf switch becomes a broadcast bridge for my classic vlan to the other switches.

The 9k config guide helpfully tells me under the heading “Cisco Nexus 9000 as Hardware-Based VXLAN Gateway”

"This type of VXLAN-to-VLAN connectivity is enabled by using a VXLAN gateway.

A VXLAN gateway is a VTEP device that combines a VXLAN segment and a classic VLAN segment into one common Layer 2 domain".

BUT gives no indication as to how this is configured / tested / verified nor a description of forwarding behaviour.

Q1. How does a VXLAN configured switch treat bcast and L2 traffic from 802.1q trunks?

Q2. Are you mandated to run STP when connecting classic vlan domains to VXLANS?

Q3. How do you configure a VXLAN L2 domain to a classic vlan L2 domain as a (L2) VXLAN gateway.

Revelation78 · ‎05-20-2017

Let's see if I understand your questions correctly.

Q1) It will treat them as any originating port in terms of traffic.

Q2) STP should be run on no-VXLAN devices

Q3) There's nothing extra to configure. Your EVPN configuration exists on your 9K. You have a port or ports configured as a L2 trunk from your legacy network on your 9k. These will be configured as simply trunk ports.

When the traffic, VLAN tagged, from the legacy network comes across the trunk link; the 9K will automatically put that traffic into the VXLAN / EVPN fabric. This is no different if you had a server or UCS attached to your 9K.

What you will need to pay attention to is where the Default Gateway lives. If your DG lives in the legacy environment then you will not configure an SVI / Anycast gateway in the EVPN environment. That VXLAN will remain L2 only.

This is the process by which we "VLAN Stretched" a legacy environment into our new greenfield DC project. If you have any further questions, feel free to ask away; over the last year I have become intimately familiar with EVPN / VXLAN.