Network Layer Functions Key Layer in Internet Architecture End-to-end Packets Adapt to lower layers

Network Layer Design Goals –‘Independent’ of layer 1 & 2 implementations –Hide layer 1 & 2 details from upper layers Architecture –Connection oriented –Connectionless –(where should reliability be done?) Services –Routing (Path selection) –Adaptation to different lower layers

Routing Algorithms Goals –Optimality –Fairness –Stablility –Robustness –Correctness –Simplicity Adaptive vs Static Congestion Control

Adaptive Routing Centralized Isolated Distributed

Distributed Routing Metric - Vector Algorithms –sometimes called shortest path –Bellman-Ford most famous –Knowledge of immediate neighbors –Result is “first step” in path to ultimate destination Link State Algorithms –OSPF {Open Shortest Path First} –Knowledge of network layer map (connectivity)

Congestion Control RESEARCH ISSUE! Resource Reservation Packet Discarding Flow Control

Routing Information Protocol (RIP) Known as a routing table update protocol Developed by Xerox and gained widespread acceptance by the proliferation of TCP/IP’s implementation of it in UNIX. Other protocols (AppleTalk, NetWare) adopted RIP as their standard routing update protocol. Known as a distance vector protocol. –Vector is an adjacent router and the distance is how far away (hops) the network is. –One hop is considered one router traversed. Devised for relatively stable, small-to-medium size networks (less than 16 routers in diameter).

Calculating the Cost Network 1 Network 2 Network 3 Network 4 Network Hops Network Hops Network Hops Transmitted routing table Transmitted routing table Internal routing table Router A Router B Router C

IP Routing Making Decisions Gathering Information ICMP

Routing Table NetworkMaskRouterHopsAgePort ID C C B B

Example: TCP/IP Not the only way to do things... But well tested in the field Brief History TCP/IP vs ISO protocols

References TCP/IP Overall -- Douglas Comer –Internetworking with TCP/IP, Vol I, 3d ed. –Internetworking with TCP/IP, Vol II –Internetworking with TCP/IP, Vol III (Sockets) –Internetworking with TCP/IP, Vol III (TLI) Unix Programming -- W. Richard Stevens –Unix Network Programming –Advanced Unix Network Programming Stevens & Wright –TCP/IP Illustrated Vol I –TCP/IP Illustrated Vol II –TCP/IP Illustrated Vol III

TCP/IP Stack OSI DIX Ethernet or... ARP ICMP IP TCP UDP DNSTELNET FTP

Notes on TCP/IP Suite TCP/IP preceded the OSI Reference Model Layers 1 & 2 are not part of the standard Functions above the Transport Layer are consolidated

Brief Definitions ARP -- Address Resolution Protocol IP -- Internet Protocol ICMP -- Internet Control Message Protocol UDP -- User Datagram Protocol TCP -- Transmission Control Protocol DNS -- Domain Name System FTP -- File Transfer Protocol TELNET -- remote terminal

Other TCP/IP Protocols Routing Protocols -- RIP, OSPF, EGP, GGP BOOTP - Bootstrap Protocol RARP - Reverse ARP TFTP - Trivial FTP HTTP - Hyper Text Transfer Protocol SMTP - Simple Mail Transfer Protocol SNMP - Simple Network Management Protocol

Layer Protocols DNS Query DNS Reply SYN SYN/ACK ACK CallerCallee {TCP Establishment} ARP Request ARP Reply

IP Functionality Presents single, virtual network to user Connectionless Delivery Packet Routing Interface to Lower Layers

IP Addresses “Dotted Decimal” 32 bit (4 byte) address, written by taking each byte as an unsigned number Address Classes [first octet] –A –B –C –D - special subset of C multicast –E - reserved Netmask –a 32 bit value which, when ANDed with an address, selects only the network part

Netmask Usage “Do a bitwise AND then compare for equality of results” & netmask =?= & netmask if comparison is equal, then both src & dst are on same (sub)net. Same netmask

Netmask Examples S= M= result D= M= result Not Equal S= M= result S= M= result D= M= result D= M= result ? ?

Special Address Conventions This host Host on this net Limited broadcast Directed broadcast Loopback all 0’s 127anything (usually 1) net hostall 0’s all 1’s

IP Header VERSHLENSERVICE TYPETOTAL LENGTH FLAGSFRAGMENT OFFSETIDENTIFICATION TIME TO LIVEPROTOCOLHEADER CHECKSUM SOURCE IP ADDRESS DESTINATION IP ADDRESS 1984 IP OPTIONS (IF ANY)PADDING DATA... 24

IP Packet Handling (rcv) receiving Transport Layer (TCP or UDP) Sockets IP Link {DIX Type or DSAP} Other Physical

IP Packet Handling (xmit) sending Local or Non-Local ? ARP Search Routing Table Found!Missing! ICMP Error Send locally...

A Bridges or Routers B C D Address & Netmask 1: : : : :

ICMP ping –ECHO Request/Reply traceroute traceroute to falcon.ece.utexas.edu ( ), 30 hops max, 40 byte packets 1 exit_133 ( ) 2 ms 2 ms 2 ms 2 exit_128 ( ) 2 ms 3 ms 2 ms 3 FDDI-T3.TAMU.EDU ( ) 3 ms 3 ms 3 ms 4 FDDI-WAN.TAMU.EDU ( ) 5 ms 4 ms 6 ms 5 sprint-gw-h1-0.the.net ( ) 20 ms 5 ms 5 ms 6 ut8-h1-0.the.net ( ) 8 ms 9 ms 21 ms ( ) 7 ms 11 ms 7 ms 8 ens.gw.utexas.edu ( ) 16 ms 23 ms 21 ms 9 ece-e0.gw.utexas.edu ( ) 12 ms 9 ms 9 ms 10 * * *