SCCM and PXE Boot via the WAN - Very slow speed

Hello fellow adventurists,

we recently decided to move the DPs out of the branch offices and utilize our Datacenter DPs for OSD purposes.

Our WAN links are quite fast and -with the use of a local cache in the manner of PeerCache- should suffice.

So, after doing the proper IP Helper configuration, the client properly gets a DHCP and then the information needed to boot from our Datacenter DP, but it only reaches up to 200-300Kbyte per second on a 300Mbps WAN link,. Apparently this would make this effort without any point.

I have already modified the TFTPBlockSize to 1024 (from 16K which it was set for Local LAN traffic) in an effort to see if the WAN MTU size is more friendly with it. No change to speed.

Is there any case where someone has gone through this setup?