Solved: Understanding VXLAN packet flow

Thiyagarajan K · ‎11-28-2016

Hello All,

I'm trying to get a better picture of VXLAN packet flow and could you please help me with the following questions on Nexus 9K platform switches:

How are VXLAN ID's allocated? If it is dynamic and what would be the formula for a new VXLAN?
How VXLAN identifies the host on other VXLAN?
In the VxLAN to VXLAN traffic when will the broadcast, multicast and unicast are used?

Regards,

Thiyagu

micgarc2 · ‎11-30-2016

1) The VXLAN IDs are allocated dynamically.

2) VXLAN does not identify the host on another VXLAN. VXLAN is just an encapsulation. When traffic comes into the fabric from the user space (which can be 802.1Q, VXLAN, or NVGRE) it is received by the leaf and then translated into VXLAN. The traffic is then transported to the leaf it needs to exit on. Once it gets to the egress leaf, we then re-encapsulate into the required frame format. A device is identified by its IP address and the VNID (or leaf that it is on). L2 and L3 flow use different VNIDs to help the destination leaf understand how to forward.

3) End point behavior does not change. There are still ARP requests coming into the leaf. By default, inside the fabric, ACI does not typically broadcast or multicast. Instead, we translate the broadcast traffic from the end point into a unicast packet to send to the destination leaf and to the desired endpoint.

These resources might help you understand VXLAN more clearly.

https://www.youtube.com/watch?v=ZvITtE-gQYg

http://www.cisco.com/c/en/us/support/docs/switches/nexus-9336pq-aci-spine-switch/118930-technote-aci-00.html

http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/white-paper-c11-729383.html

View solution in original post

micgarc2 · ‎11-30-2016

1) The VXLAN IDs are allocated dynamically.

2) VXLAN does not identify the host on another VXLAN. VXLAN is just an encapsulation. When traffic comes into the fabric from the user space (which can be 802.1Q, VXLAN, or NVGRE) it is received by the leaf and then translated into VXLAN. The traffic is then transported to the leaf it needs to exit on. Once it gets to the egress leaf, we then re-encapsulate into the required frame format. A device is identified by its IP address and the VNID (or leaf that it is on). L2 and L3 flow use different VNIDs to help the destination leaf understand how to forward.

3) End point behavior does not change. There are still ARP requests coming into the leaf. By default, inside the fabric, ACI does not typically broadcast or multicast. Instead, we translate the broadcast traffic from the end point into a unicast packet to send to the destination leaf and to the desired endpoint.

These resources might help you understand VXLAN more clearly.

https://www.youtube.com/watch?v=ZvITtE-gQYg

http://www.cisco.com/c/en/us/support/docs/switches/nexus-9336pq-aci-spine-switch/118930-technote-aci-00.html

http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/white-paper-c11-729383.html