After a vPC peer device reloads and comes back up, the routing protocol needs time to reconverge. The recovering vPCs leg may black-hole routed traffic from access to core until Layer 3 connectivity is reestablished. vPC Delay Restore feature delays vPCs leg bringup on the recovering vPC peer device. vPC Delay Restore allows for Layer 3 routing protocols to converge before allowing any traffic on vPC leg. Result is a more graceful restoration and zero packet loss during the recovery phase (traffic still get diverted on the alive vPC peer device). This feature is enabled by default with a vPC restoration default timer of 30 seconds. The timer can be tuned according to a specific Layer 3 convergence baseline from 1 to 3600 seconds. Reference: https://www.cisco.com/c/dam/en/us/td/docs/switches/datacenter/sw/design/vpc_design/vpc_best_ practices_design_guide.pdf