Why can't I just route my AMPRNet allocation directly myself ?
Reason #1: Because of Ingress Filtering
In order to combat these attacks, most Internet Service Providers have adopted practices defined by the Internet Standards BCP38 and BCP84. Two of these practices are ingress filtering and Unicast Reverse Path Forwarding.
These practices prevent IP address spoofing by blocking packets whose IP source address is not the in the IP subnet range where the packet originated.
If your ISP implements these practices (and they should), you will be unable to transmit packets using your AMPRNet allocation as the source address directly from your home network.
Reason #2: Restrictions on who can announce routes
In order to prevent chaos on the Internet only ISP's and other authorized networks can announce routes globally. Your ISP will block any attempts by you to advertise your AMPRNet allocation without their permission. In addition, announcing your AMPRNet allocation directly, without the permission of the AMPRNet network administrator is a violation of AMPRNet's Terms of Service and Acceptable Use Policy.
The two ways around these restrictions are: