Question: My nodes appear to be getting DHCP from my CSN, so why won't they boot a CSN image?
Answer: It is very likely that you do not have portfast configured on the switchports leading to the Swarm nodes. Assuming Spanning Tree Protocol is enabled on the switch (and it should always be), then any newly connected host must pass through several Spanning Tree states (listening, learning, and only then forwarding) before the node becomes available via the network. Because of this, the node is not available when netboot needs to deliver the Swarm image/ configuration. Please ensure that any port leading to any Swarm product is configured with portfast.
It is easy to figure out if portfast is configured. Simply look at the switchport configuration. If you do not see it configured, it is not enabled. That is not a feature that would be enabled by default.
You also may have Netboot Protect configured on the CSN- especially with Single Network CSNs, this is the default.