tcp

Transmission Control Protocol. Originated along with ipv4 and hence the entire system is called TC/IP. It’s IP Protocol Number is 6.

• IP packets may be lost, duplicated or out of order due to network congestion. TCP’s job is to rectify these errors.

• Since it focuses on reliable connection rather than fast connection it may take a lot of time to deliver the addresses.

• The sender keeps a timer and the receiver returns an acknowledgement on receiving the packet. If the timer expires before the acknowledgement is received, the packet is dropped immediately.

• Contains checksum verifications and sequence numbers to maintain data integrity.

• Can also selectively receive packets in broken sequences, say 1000-2000 and then 3000-3089. In this case, a flag called SACK (Selective Acknowledgement) can be set to 1, that allows the receiver to receive discontinuous blocks like these.

• Usually TCP waits for the full packet to be created before it it sent. However, PSH flag can be used for sending data immediately without waiting for the buffer to get full.

Vulns

• TCP Veto: Add a malicious packet in between with a sequence number same as the one going to arrive next. The next one is silently dropped a duplicate one. This isn’t highly controllable but very resistant to detection.

• Sequence prediction attacks: Create an entire sequence of packets and hijack the network to pretend you are the host.