Chapter 4 Network Layer Computer Networking: A Top Down Approach 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:  If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!)  If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright J.F Kurose and K.W. Ross, All Rights Reserved Network Layer 4-1

Lecture 11 (Contd.) University of Nevada – Reno Computer Science & Engineering Department Fall 2015 CPE 400 / 600 Computer Communication Networks Prof. Shamik Sengupta Office SEM 204

Network Layer 4-3 Network Layer

4-4 The Internet network layer forwarding table host, router network layer functions: routing protocols path selection RIP, OSPF, BGP IP protocol addressing conventions datagram format packet handling conventions ICMP protocol error reporting router “signaling” transport layer: TCP, UDP link layer physical layer network layer

Network Layer 4-5 ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier header checksum time to live 32 bit source IP address head. len type of service flgs fragment offset upper layer 32 bit destination IP address options (if any) IP datagram format IP protocol version number header length (bytes) upper layer protocol to deliver payload to total datagram length (bytes) for fragmentation/ reassembly max number remaining hops (decremented at each router) e.g. timestamp, record route taken, specify list of routers to visit. how much overhead?  20+ bytes of TCP  8 bytes for UDP  20 bytes of IP  = 40 bytes + app layer overhead

Network Layer 4-6 IP fragmentation, reassembly  network links have MTU (max. transfer size) - largest possible link-level frame  different link types, different MTUs  large IP datagram divided (“fragmented”) within net  one datagram becomes several datagrams  “reassembled” only at final destination  IP header bits used to identify, order related fragments fragmentation: in: one large datagram out: 3 smaller datagrams reassembly … …

Network Layer 4-7 ID =x offset =0 fragflag =0 length =4000 ID =x offset =0 fragflag =1 length =1500 ID =x offset =185 fragflag =1 length =1500 ID =x offset =370 fragflag =0 length =1040 one large datagram becomes several smaller datagrams example:  4000 byte datagram  MTU = 1500 bytes 1480 bytes in data field offset = 1480/8 IP fragmentation, reassembly Why divide by 8?

Network Layer 4-8 IP addressing: introduction  IP address: 32-bit identifier for host, router interface  interface: connection between host/router and physical link  router’s typically have multiple interfaces  host typically has one or two interfaces (e.g., wired Ethernet, wireless )  IP addresses associated with each interface =

Network Layer 4-9 Subnets  IP address:  subnet part high order bits  host part low order bits  what’s a subnet ?  device interfaces with same subnet part of IP address  can physically reach each other without intervening router network consisting of 3 subnets subnet

Network Layer 4-10 recipe  to determine the subnets, detach each interface from its host or router, creating islands of isolated networks  each isolated network is called a subnet subnet mask: /24 Subnets / / / subnet

Network Layer 4-11 how many? Subnets

Lecture 12 University of Nevada – Reno Computer Science & Engineering Department Fall 2015 CPE 400 / 600 Computer Communication Networks Prof. Shamik Sengupta Office SEM 204

Announcements  Assignment 2 uploaded, Due by Wednesday, Oct 13 th  Quiz 2 on Wednesday, Oct 7th Introduction 1-13

IP Address classes Address ClassRange of IP addresses Class A Class B Class C Class D

Some special IP addresses  – lowest IP address  Not used for a host connected to the Internet  Used for hosts when they start (boot)  – highest IP address  Not used for a host  Used for broadcasting

“Classful” IP addressing problem  Suppose you have a company with 200 hosts. Which IP address class would you choose and why?  Suppose you have a company with 300 hosts. Which IP address class would you choose and why?

Network Layer 4-17 IP addressing: CIDR CIDR: Classless InterDomain Routing  subnet portion of address of arbitrary length  address format: a.b.c.d/x, where x is # bits in subnet portion of address subnet part host part /23

Network Layer 4-18 IP addresses: how to get one? Q: How does a host get IP address?  hard-coded by system admin in a file  DHCP: Dynamic Host Configuration Protocol: dynamically get address from a server  “plug-and-play ”

Network Layer 4-19 DHCP: Dynamic Host Configuration Protocol goal: allow host to dynamically obtain its IP address from network server when it joins network  can renew its lease on address in use  allows reuse of addresses only hold address while connected  support for mobile users who want to join network DHCP overview:  host broadcasts “DHCP discover” msg  DHCP server responds with “DHCP offer” msg  host requests IP address: “DHCP request” msg  DHCP server sends address: “DHCP ack” msg

Network Layer 4-20 DHCP client-server scenario / / / DHCP server arriving DHCP client needs address in this network

Network Layer 4-21 DHCP server: arriving client DHCP discover src : , 68 dest.: , 67 yiaddr: transaction ID: 654 DHCP offer src: , 67 dest: , 68 yiaddrr: transaction ID: 654 lifetime: 3600 secs DHCP request src: , 68 dest:: , 67 yiaddrr: transaction ID: 655 lifetime: 3600 secs DHCP ACK src: , 67 dest: , 68 yiaddrr: transaction ID: 655 lifetime: 3600 secs DHCP client-server scenario

Network Layer 4-22 DHCP: more than IP addresses DHCP can return more than just allocated IP address on subnet:  address of first-hop router for client  name and IP address of DNS sever  network mask  indicating network versus host portion of address

4-23  connecting laptop needs  its IP address,  addr of first-hop router,  addr of DNS server  use DHCP router with DHCP server built into router  DHCP request  encapsulated in UDP,  encapsulated in IP,  encapsulated in Ethernet  Ethernet frame broadcast on LAN,  received at router running DHCP server  Ethernet  to IP  to UDP  to DHCP DHCP UDP IP Eth Phy DHCP UDP IP Eth Phy DHCP DHCP: example

Network Layer 4-24  DCP server formulates DHCP ACK containing  client’s IP address,  IP address of first-hop router for client,  name & IP address of DNS server  encapsulation of DHCP server,  frame forwarded to client,  up to DHCP at client DHCP: example router with DHCP server built into router DHCP UDP IP Eth Phy DHCP UDP IP Eth Phy DHCP  client now knows  its IP address,  name and IP address of DNS server,  IP address of its first- hop router

Network Layer 4-25 DHCP not enough! NAT

Network Layer 4-26 NAT: network address translation local network (e.g., home network) /24 rest of Internet datagrams with source or destination in this network have /24 address for source, destination (as usual) all datagrams leaving local network have same single source NAT IP address: ,different source port numbers

Network Layer 4-27 motivation: local network uses just one IP address as far as outside world is concerned:  range of addresses not needed from ISP:  just one IP address for all devices  can change addresses of devices in local network without notifying outside world  can change ISP without changing addresses of devices in local network  devices inside local net not explicitly addressable, visible by outside world  a security plus NAT: network address translation

Network Layer 4-28 implementation: NAT router must:  outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #)... remote clients/servers will respond using (NAT IP address, new port #) as destination addr  remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair  incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table NAT: network address translation

Network Layer S: , 3345 D: , : host sends datagram to , 80 NAT translation table WAN side addr LAN side addr , , 3345 …… S: , 80 D: , S: , 5001 D: , : NAT router changes datagram source addr from , 3345 to , 5001, updates table S: , 80 D: , : reply arrives dest. address: , : NAT router changes datagram dest addr from , 5001 to , 3345 NAT: network address translation

Network Layer 4-30  NAT is controversial:  routers should only process up to layer 3  violates end-to-end argument  address shortage should instead be solved by IPv6 NAT: network address translation

Network Layer 4-31 NAT traversal problem  client wants to connect to server with address  server address local to LAN client can’t use it as destination addr  only one externally visible NATed address:  solution: Port forwarding: statically configure NAT to forward incoming connection requests at given port to server  e.g., ( , port 2500) always forwarded to port NAT router client ?

Network Layer 4-32 NAT traversal problem  Solution 2: relaying (used in Skype)  NATed client establishes connection to relay  external client connects to relay  relay bridges packets between two connections client 1. connection to relay initiated by NATed host 2. connection to relay initiated by client 3. relaying established NAT router

Sample Project Topics CPE 400  Simulation  WiFi Medium access control  ARP and ARP spoofing  Statistical multiplexing in flow control of routers in a network  Optimized Link State Routing (OLSR) Protocol  Better Approach To Mobile Adhoc Networking (B.A.T.M.A.N.)  Routing in VANET/FANET  Multicasting and group management CPE 600  Research Survey Topics  D2D Communication for future 5G networks  Platoon-Based Vehicular Cyber- Physical Systems Architecture and Challenges  Internet-of-Things (IoT) Self-organization Security and privacy issues  Software Defined Networks  Interference mitigation in Femtocells  Crowdsourcing in Heterogeneous Networked Environments Introduction 2-33

Some more sample project topics CPE 400  Simulation  Transmission power/sleep control in sensor networks for extended lifetime  Data aggregation at routers/sensors for bandwidth conservation  Performance of existing routing protocols under error prone networks  Experimenting with positioning technologies for mobile networks  Any kind of system development based on networking Introduction 2-34

CPE 400 Requirements  Basic requirement  The program is running, compiling and giving output  The program is able to simulate the protocol/application scenario well as explained in the documentation  You are able to capture the basic functionalities of the protocol/application  There are results (performance results)  Some explanations of the results  Advanced requirement  You are able to handle ALL the format / functionalities of the protocol/ application  You are able to handle the error use case scenarios  You are able to tweak the existing platform/mechanism to come up with something else that are focused on something extra  Able to compare with another similar protocol  Able to get some results on your proposed idea  And explanations… Introduction 2-35