Subject: [spring] comments and suggestions to draft-dukes-sr-for-sdwan-01

From: Linda Dunbar <[email-masked]>
Date: Mon, 30 Apr 2018 21:19:14 +0000

Darren, et al,

Most of your document is focused on SD-WAN end points directly attached to SR PE nodes.
SD-WAN, as described by ONUG (Open Network User Group), is about pooling WAN bandwidth from n service providers to get better WAN bandwidth management, visibility & control. Classic SD-WAN between two end points E1 <-> E2 may have one (or two) SP managed path (e.g. MPLS path) and one 3rd party (e.g. public internet) path. [Let's call it Classic SD-WAN]
Is your document mainly about how using SR to make the SP managed path between E1<->E2 provide the needed SLA?

Your document is not about how to use SR (or the principle of SR as SD-WAN head nodes may not support SR) to steer as much portion of SD-WAN path to SP managed VPN to maximize performance? As I have explained to you during IETF 101?
In this case, the SD-WAN end nodes are not directly attached to SP VPN (e.g. workloads in Cloud DCs).  Simple SD-WAN path can traverse public internet, but can have unpredictable performance if the end points are far apart (across states, or across countries. Therefore, it is highly desirable to have bigger portion of the SD-WAN over provider VPN to maximize E2E performance, as shown in the diagram below.

Under this circumstance, SD-WAN end-points usually can reach multiple PEs. In the diagram above, E1 <-> E2 SD-WAN (most likely IPsec tunnel) path can traverse C1 <-> C4, C1<->C6, C3<->C6, or C3<->C4 within the VPN. There are many flows (by different Apps) between E1 <-> E2. Some flows may need to traverse C1<->C4, others may need to traverse C3<->C6 or other segments within the VPN, which are determined by the SD-WAN controller based on the characteristics & need of the Apps, such as cost, available bandwidth, latency, or special functions only available at specific locations, etc.
Even with the same ingress/egress, some flows may need different segments across the provider VPN. It is not practical, or even possible, for PEs (e.g. C1, C2, C3 in this example) to differentiate which flows should egress C4 or C6 where both C4&C6 can reach E2.
Segment Routing can easily force the path to traverse the explicit egress node (C4 or C6), or explicit segments through the provider VPNs based on the SLA requested by the SD-WAN head end nodes.

Linda Dunbar