Route Propagation
Automatically inserting routes learned from a VPN or dedicated connection into a route table, rather than maintaining them by hand.
In a hybrid network, the cloud side must know which ranges live on-premises and the on-premises side must know the cloud ranges. Static routes work and drift; propagation learns them dynamically via BGP.
Two failure modes worth knowing. Propagation disabled on a route table means traffic to on-premises follows the default route instead — usually to a NAT gateway and out to the internet, where it is dropped. The symptom is a connection that fails only from certain subnets.
Route limits: route tables have a maximum entry count, and an on-premises network advertising many specific prefixes can exceed it, causing routes to be silently dropped. The remedy is summarising advertisements on the on-premises side rather than raising the limit.
Asymmetric routing — traffic leaving by one path and returning by another — is the third recurring problem, and it breaks stateful firewalls.