PJC CCNA Semester 2 Ver. 3.0 by William Kelly Intermediate TCP/IP PJC CCNA Semester 2 Ver. 3.0 by William Kelly

The TCP/IP Protocol Suite Standard for Internetwork Communications TCP/IP closely maps to the OSI model and is helpful in understanding other protocols TCP/IP includes layer 3 and 4 protocols as well as upper layer protocols

OSI vs. TCP

Common TCP Protocols DNS – Domain Name Server WINS – Windows Naming Service HOSTS – Static IP mapping file POP3 – Post Office Protocol SMTP – Simple Mail Transfer Protocol FTP – File Transfer Protocol TFTP – Trivial File Transfer Protocol HTTP – Hypertext Transfer Protocol

Troubleshooting Protocols Telnet - used for testing the application layer Packet Internet Groper (ping) – used for lower layer testing traceroute – used to find a break in the internetwork path between the source and the destination networks

Windows Troubleshooting Protocols NBSTAT- used to troubleshoot NETBIOS name resolution NETSTAT – useful to summarize TCP/IP connections ipconfig/winipcfg – displays the current network settings (IP address of host, mask, gateway, and DNS information)

Transport Layer key points Protocols (TCP and UDP) Flow Control/Windowing Data Reliability 3-way handshakes Denial of Service Ports

Layer 4: Transport Layer TCP vs. UDP Connection-oriented Reliable Messages divided into segments Reassembles at destination Resends data that is not acknowledged Connectionless Unreliable Messages are called datagrams Software checking of message delivery No reassembly of messages No acknowledgements No Flow Control

Transport Layer Protocols: TCP Segment Format

Transport Layer Protocols: UDP Segment Format Notice port numbers are used in the formation of both UDP and TCP segments

Flow Control and Windowing Flow control is the regulation of how much data is sent during a transmission period and windowing is the process of flow control TCP breaks down large pieces of data into segments suitable for transmission Windows size determines how many segments can be sent before acknowledgement A sliding window adjusts the number of segments sent to cope with congestion or slow processing by the destination host

Data Reliability Reliability is provided in 3 ways: Sliding windows Controls the amount of information transferred Congestion avoidance and control Allows more than one segment to be sent before acknowledgement Positive acknowledgement with retransmission Synchronization Sequence numbers Sequencing of segments at source before transmission

3 Way Handshakes TCP allows a synchronization process prior to data transmission that forms a virtual circuit Sequence numbers included in the handshake assure that positive acknowledgements can be made to the connection request and to transmitted segments (Remember IP provides no verification that data was transmitted successfully)

3 Way Handshakes (cont.)

Denial of Service Attacks During Synchronization Syn Flooding is one type of DOS that uses a false source IP address during a 3 way handshake causing a reply to a non-existent address. This fills up the connection queue and exhausts system resources. Possible defenses include: Decreasing the connection timeout Increasing the size of the connection queue

Ports Ports are represented by a 16 bit number ( 0 -65,535 possible) Three types of ports are: Well Known – 0 – 1023 Registered – 1024 – 49,151 Dynamic or Private – 49,152 – 65,535 A port number and an IP address for a socket Usually clients randomly assign source port numbers Note: Numbers below 255 are for public applications, numbers between 255 and 1023 are assigned to companies for marketable applications, and numbers above 1023 are unregulated

Important Port Numbers!!

Internet Layer Protocols IP – connectionless best-effort system to move datagrams to a destination ICMP – Provides control and messaging ARP – Address Resolution Protocol determines a MAC address for a known IP address RARP – Reverse Address Resolution Protocol determines an IP address for a known MAC address (diskless workstations)