1. Review the key networking concepts –TCP/IP reference model –Ethernet –Switched Ethernet –IP, ARP –TCP –DNS

3. FTP data can be infinitely large, when do we chop it into smaller Units?

4. Internetworking devices –Repeaters: PHY device that restores data and collision signals –Hub: Multiport repeater –Bridge: Datalink layer device connecting two or more collision domains (extended LAN). MAC multicasts are propagated throughout the extended LAN –Switch: Multiport bridge with parallel paths –Router: Network layer device. –Network address translator (NAT): Transport layer device. –Gateways: Transport layer or application layer devices

6. Ethernet –Shared medium LAN technology –Need medium access control CSMA/CD + binary exponential backoff –Frame format: |Preamble|Start|Dst Addr|Src Addr|length| Data | Pad |Checksum 7 1 6 6 2 0-1500 0-46 4 Minimum data + pad length: 46 bytes Maximum data length: 1500 bytes

8. Fast Ethernet (100Mbps) –Reduce cable length and keep everything else –Duplex mode Gigabit Ethernet (1000Mbps) –Reduce cable length and increase minimum frame size –Duplex mode

9. Switched Ethernet –Get dedicated link in Ethernet in a transparent manner. –Issue: the switch needs to know where to forward a packet –How is it accomplished? Self-learning algorithm to obtain the location of each machine Forwarding algorithm –Can switched Ethernet take advantage of the dense connectivity in the network topology? Spanning tree algorithm

10. IP –Addressing (type, network number, host number) Class A, Class B, Class C –Classless inter-domain routing IP address + prefix length e.g. 192.168.0.3/22

13. IP header format: –Version (4 bits): IPv4, IPv6 –Header length (4 bits): in 32-bit words, min header is 5 words or 20 bytes –Type of service (8 bits): reliability, precedence, delay, and throughput. Used in DiffServ (IP QoS support) –Total length (16 bits): header + data in bytes, total must less than 64 KB. –Identifier (16 bits): uniquely identify the datagram during its life for a given source and destination addess.

14. IP header format: –Flags (3 bits): more flag, no-fragmentation –Fragment offset (13 bits): in units of 8 bytes –Time to live (TTL): specified in router hops –Protocol: next level protocol to receive the data –Header checksum: 1’s complement sum of all 16 bit words in the header –Source/destination address: original source/destination –Options (variable): Security, source route, record route, timestamp recording –Padding (variable): makes header length a multiple of 4 –Data (variable): data + header <= 65535 bytes.

15. IP functionality: –Framentation –Addressing –Routing is done by other protocols IP router –Routing: computes the next hop for each destination. –Forwarding: based on the destination address in an IP packet, forward the packet to the right next hop Longest prefix matching

16. Internet Routing protocols –RIP: distance vector algorithm –OSPF: link state algorithm –BGP: path vector algorithm that supports policy based routing

18. TCP segment structure source port # dest port # 32 bits application data (variable length) sequence number acknowledgement number Receive window Urg data pnter checksum F SR PAU head len not used Options (variable length) URG: urgent data (generally not used) ACK: ACK # valid PSH: push data now (generally not used) RST, SYN, FIN: connection estab (setup, teardown commands) # bytes rcvr willing to accept counting by bytes of data (not segments!) Internet checksum (as in UDP)

19. TCP header –Source port (16 bits): identifies the source process. 20=FTP, 23=Telnet, 80=HTTP. –Destination port (16 bits) –Sequence Number (32 bits): Sequence number of the first byte in the segment. If SYN is present, this is the initial sequence number (ISN) and the first data byte is ISN+1 –ACK number (32 bits): Next byte expected –Data offset (4 bits): number of 32-bit words in header –Reserved (6 bits)

20. TCP header –Control (6 bits): URG urgent pointer field significant ACK: ACK field significant PSH: push function RST: reset the connection SYN: synchronize the sequence number FIN: no more data from sender –Window (16 bits): wil accept [ack] to [ack+window] –Checksum (16 bits): cover the header plus a pseudo header.

21. TCP header –Urgent pointer (16 bits): points to the byte following urgent data. –Options (variable): max segment size, window scale factor, etc.

23. Each computer has a name resolver routine (gethostbyname in UNIX) Each resolver knows the name of a local DNS server Resolver sends a DNS request to the server DNS server either gives the answer, forwards the request to another server, or gives a referral –Recursive query / iterative query Referral = next server to whom the request should be sent