What‘s the purpose of using BGP in VXLAN?

[JaySu]

As I know, VXLAN uses OSPF for its underlay. However, it seems BGP is involved in the underlay, but I cannot figure out the purpose.

A VTEP encapsulates a packet, and if OSPF is deployed, every device should be able to route the packet to another VTEP via the outer-MAC and outer-IP. What BGP actually does in the VXLAN?

[Reza Sharifi]

Apparently you have to have BGP.

Routing at the VTEP - A high level view

Mandatory configurations

1. A VLAN is configured for each segment - sending segment, VRF segment and receiving segment.

2. BGP and EVPN configurations ensure redistribution of this information across the VXLAN setup.https://www.cisco.com/c/en/us/td/docs/switches/datacenter/pf/configuration/guide/b-pf-configuration/Introducing-Cisco-Programmable-Fabric-VXLAN-EVPN.htmlHTH

[JaySu]

Thanks for your information. I just finished it. There are another questions:

1.) If VTEPs advertises every end host’s information while they attach, in what circumstance ARP request is needed? Will the information timeout?

2.) As I know, EVPN seems to be related to MPLS. I would like to ask how SPINEs route the packets? Do they parse the outer-IP and look up their routing table?

[canero]

1.) If VTEPs advertises every end host’s information while they attach, in what circumstance ARP request is needed? Will the information timeout?
VTEP as knowing the MAC, IP Addresses of the remote Host, it may reply to an ARP Request from a locally attached host. This is also known as ARP Suppression because the ARP Request broadcast packet does not go (doesn't need to go) across the Fabric links to the Remote host to reply as it is already known by the VTEP.
For this reason Data Plane Learning mechanisms as Multicast replication and Ingress replication are not needed reducing traffic and provides more scalable solution with MP-BGP.



2.) As I know, EVPN seems to be related to MPLS. I would like to ask how SPINEs route the packets? Do they parse the outer-IP and look up their routing table?
EVPN Vxlan looks similar to MPLS (VPLS) as both provide L2 reachability across a L3 domain with Tunneling technologies.
If a Vxlan traffic arrives from a VTEP to the SPINE going out, Vxlan needs to be changed to Vlan so that non Vxlan device may understand how to classify the traffic since it does not understand from Vxlan VNID.

[canero]

If there are 10 vteps(switches), how could VTEP1 know to send packet through Vxlan to VTEP8, and not VTEP6? It looks to BGP table where the table of Mac, VTEP pairings exist