Ethernet (or at least TCP) packet debugging with the ability to set breakpoints and modify packets

Fiddler is an HTTP proxy that, among other things, allows one to pause outgoing and incoming HTTP packets, modify their conte开发者_如何转开发nts and continue.

Is there anything similar to this working in lower layers of the OSI model? In particular, I want to be able to pause a TCP ACK packet and later let it continue through the pipeline. *nix or Windows suggestions are appreciated.

These two tools might be of interest to you.

From the Wireshark Tools Wiki:

Nemesis is a command-line network packet crafting and injection utility. Nemesis can natively craft and inject ARP, DNS, ETHERNET, ICMP, IGMP, IP, OSPF, RIP, TCP and UDP packets. (GPL, BSD/Linux/Solaris/Mac OSX/Win32)

You might also want to check out Winsock Packet Editor:

WPE Pro 0.9a (Windows XP, 2003, Vista, 7), 1.3 (Windows 95, 98, ME, 2000) Winsock Packet Editor (WPE) Pro is a packet sniffing/editing tool which is generally used to hack multiplayer games. WPE Pro allows modification of data at TCP level. Using WPE Pro one can select a running process from the memory and modify the data sent by it before it reaches the destination. It can record packets from specific processes, then analyze the information. You can setup filters to modify the packets or even send them when you want in different intervals. WPE Pro could also be a useful tool for testing thick client applications or web applications which use applets to establish socket connections on non http ports.