Building Next-Generation Data Center

Starting on April 25th

Register now!

BGP in EVPN-Based Data Center Fabrics

ipSpace.net » Documents » Using BGP in a Data Center Leaf-and-Spine Fabric » BGP in EVPN-Based Data Center Fabrics

In this section, we’ll focus on running EVPN with VXLAN or MPLS encapsulation within a single data center fabric and not consider the implications of running EVPN between data center fabrics, where a robust implementation would need at least for some minimal broadcast domain isolation on fabric edge.

EVPN is implemented as a BGP address family that can be run over IBGP or EBGP connections. You can therefore use either IBGP or EBGP to build EVPN infrastructure within a single data center fabric.

However, as the spine switches should not be involved in intra-fabric customer traffic forwarding regardless of whether your implementation uses MPLS or VXLAN encapsulation, the BGP next hop in an EVPN update must not be changed on the path between ingress and egress switch – the BGP next hop should always point to the egress fabric edge switch.

Running EVPN over EBGP: BGP next hop must be preserved

Conclusion: if you want to exchange EVPN updates across EBGP sessions within a data center fabric, the EVPN implementation must support functionality equivalent to MPLS/VPN Inter-AS Option C: BGP next hop must not be changed on EBGP updates.

Not all vendors have seamlessly integrated EVPN with EBGP, so you might encounter interesting vendor limitations like:

  • EVPN is supported only on IBGP;
  • EVPN is supported on EBGP but the vendor does not support next-hop-unchanged on EBGP sessions;
  • Configuring EVPN over EBGP involves many more configuration tweaks than configuring EVPN with IBGP.

In these cases, run EVPN over IBGP sessions assuming you can use an IGP as your routing protocol. Run away from vendors that try to sell you the idea of running EBGP between leaf and spine switches, and IBGP between leaf switches on top of intra-fabric EBGP.

Running IBGP/EVPN over EBGP/IPv4 is a broken design that shall not be used

More information

  • Leaf-and-Spine Fabric Architectures webinar gives you plenty of Data Center BGP design guidelines, including introduction to EVPN. The upcoming EVPN Technical Deep Dive webinar will cover EVPN in more details.
  • If you need a deeper understanding of data center fabric designs, check out the Designing and Building Data Center Fabrics online course.
  • A good data center networking engineer or architect understands the networking technologies and design guidelines. A great networking engineer or architect understands the needs and limitations of the whole stack of technologies and architectures, including compute, storage, and network services. You'll get that in the Building Next-Generation Data Center online course.

Table of Contents

Upcoming

  • Impact of MPLS/VPN