Planning guidelines

1. Our design relies heavily on the loopback, which uniquely identifies each SD-WAN node within the overlay network. It is used for BGP termination, ADVPN 2.0 operation, ADVPN shortcut monitoring and more.

   • During the design stage, we must allocate a single subnet summarizing all the loopbacks (the loopback summary).

   • Additionally, in multi-regional deployments with Inter-Regional ADVPN support, the loopbacks must be split between the regions in such a way that they can be summarized also per-region (the regional loopback summary). As you have seen previously, this summary will be advertised between the Hubs.

   • Finally, in a mixed deployment, each regional loopback summary must be further split between the Spokes using the RR-based design and those using the RR-less Dynamic BGP design. This is needed to simplify the configuration of the BGP peering on the Hubs.

     For example, the loopback summary might be 10.200.0.0/14, which is further split into multiple regional loopback summaries 10.200.1.0/24, 10.200.2.0/24, and so on. Then, assuming that the existing (RR-based) sites are using the lower loopback IPs, we can allocate the 10.200.1.128/25 range to the new sites that will use the RR-less design.

   Note that the loopbacks discussed here have significance only within the SD-WAN overlay network. They will never be advertised outside of the overlay network and will not interfere with the rest of the environment.

   The size of the loopback subnet is determined by the size of the SD-WAN network: it must accommodate all the SD-WAN nodes (Hubs and Spokes). Be careful when splitting it into regional loopback subnets! Each regional subnet must be large enough to accommodate all the SD-WAN nodes in that region!

2. It is also highly recommended to plan the LAN subnets, especially in a multi-regional deployment. With the Dynamic BGP design, summarization is always allowed on the Hubs. If the regional LAN networks can be summarized, this will greatly improve the overall scaling of the SD-WAN overlay network.

   Unfortunately, it is understood that in many real-world networks this will not be possible. Unlike the loopback addressing (which resides only within the SD-WAN overlay network), the LAN addressing can be directly dictated by the network environment beyond our control.

Make sure you consult the SD-WAN Deployment for MSSPs Guide for more details and follow the recommended configuration approach!