Is it possible to either drop a packet or alter a response using SharpPcap? I've been looking online and I've seen older posts that make it seem like it is not possible to drop a packet. I can't tell if it is possible to alter one though.
If not, can someone point me in the direction of some resources on how to do this?
Nope. libpcap/winpcap/airpcap provide observation of packets in the system but are not at the level of firewalls in that they aren't given access to the packet stream as it is coming in/out of the network adapter.
There are other pieces of software that are likely to provide support for doing just what you want, and you could still use Packet.Net with them (the packet analysis library used by SharpPcap).
