Traffic path selection when the edge is connected to multiple Hubs.
Article ID: 375430
Updated On:
Products
Issue/Introduction
When the edge is connected to two hubs and is forwarding traffic via backhaul , if one of those hubs has fewer link count than the other hub, the edge will forward the traffic depending on the hub order rather than the available links on both hubs.
Cause
The edge will always prefer the Hub according to the configured hub order, even if the hub 1 has fewer links/lower bandwidth than hub 2 as long as there's a path towards the 1st hub and has reachable routes, the edges will forward the traffic to that hub.
Only when hub 1 links are down/no VCMP tunnels built towards that hub or if no routes are reachable via that hub will the edge pick hub 2 to forward the traffic to.
Resolution
This is per design, the hub order is the factor that the edge uses to determine how to forward the traffic but not the number of links nor the amount of bandwidth available for each hub.
Additional Information
This is also the case for Hub clustering https://docs.vmware.com/en/VMware-SD-WAN/6.0/VMware-SD-WAN-Administration-Guide/GUID-3684E293-67B8-48DF-BC46-95A65594816B.html
When a Spoke is connected to primary and secondary Hub Cluster and learns same route from both of them, the route order is based on BGP attributes. If the routing attributes are same, then route sorting happens based on VPN Hub order configuration. On the other hand, the Spoke's subnets are redistributed by primary and secondary Hub or Hub Cluster to their neighbor with metric (MED) 33 and 34 respectively. You must configure "bgp always-compare-med" in the neighbor router for symmetric routing."
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