Final conclusion for Internet local breakout with two Internet WAN links
When link steering is “Auto”:
For Internet local breakout new flow, the SD-WAN Edge selects the GREEN WAN link over YELLOW/RED link. In the situation where multiple GREEN WAN links are available, SD-WAN Edge selects the WAN link with the highest remaining downstream bandwidth. The “remaining downstream bandwidth” is calculated by:
Remaining downstream bandwidth = configure/discovered downstream bandwidth – consumed downstream bandwidth
In addition, when picking the WAN link with the highest remaining downstream bandwidth, the SD-WAN Edge does not care if the WAN link is very GREEN (such as 0ms latency) or the WAN link is barely GREEN (such as 22ms latency). As long as the WAN link is GREEN, that link is entitled to be selected based on the remaining downstream bandwidth.
Upstream bandwidth consumption is not in the link selection consideration. There is no source IP address persistence (for link steering “Auto”).
When link steering is “Preferred”:
For Internet local breakout new flow, SD-WAN Edge will select the configured preferred WAN link, regardless what is that WAN link downstream bandwidth utilization. However, the configured preferred WAN link still needs to meet the link quality (packet loss, jitter, latency) SLA. If the link quality SLA is not met and there is other GREEN link available, the SD-WAN Edge will select other GREEN link for new flow. In addition, if the configured preferred WAN link is down, the SD-WAN Edge will select other available link for new flow.
Note: What exactly conditions for meeting link quality (packet loss, jitter, latency) SLA is not covered in this post.
When link steering is “Mandatory”:
For Internet local breakout new flow, SD-WAN Edge always select the configured mandatory WAN link for traffic flow. In the situation the configured mandatory WAN link is down, the traffic flow will get dropped. There is no failover to other WAN link when the link steering is Mandatory.
NOTE: When the Internet WAN link is having multiple tunnels to different SD-WAN Gateway (VCG):
Only the best quality overlay tunnel is used to determine that particular WAN link is GREEN/YELLOW/RED.
End of post “Local Internet Breakout with two Internet Links – VMware SD-WAN by Velocloud”