PXE boot not working on a new site.

- While checking a pcap, we see the client replying with error TFTP packets:

- On the WDS server, the TFTP maximum block size was reduced to 512 and the variable window extension disabled:

- Then restarted the WDS service to apply the changes and the TFTP negotiation errors stopped and PXE boot progressed further. 

- Once TFTP was stable, PXE requests started appearing in the SCCM PXE logs. However, logs showed messages like “Not serviced” and “No advertisements found”, thus, SCCM was not offering a boot image. This was due to customer's incorrect deployment configuration.

- SCCM configuration was corrected by ensuring the end host handling was correct and the client subnet was associated with the correct boundary group and PXE‑enabled distribution point.

- After fixing both the WDS TFTP settings and the SCCM configuration, PXE is now working as expected.

- TFTP maximum block size was reduced to 512 and the variable window extension disabled.

- A secondary issue was SCCM not servicing the client, which resolved by ensuring the client subnet was associated with the correct boundary group and PXE‑enabled distribution point.

- Adjusting both settings above allowed PXE boot to work correctly.