Network Layer 4-1 IP addresses: how to get one? Q: How does a host get IP address?  hard-coded by system admin in a file  Windows: control-panel->network->configuration- >tcp/ip->properties  UNIX: /etc/rc.config  DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server  “plug-and-play ”

Network Layer 4-2 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/“on”)  support for mobile users who want to join network DHCP overview:  host broadcasts “DHCP discover” msg [optional]  DHCP server responds with “DHCP offer” msg [optional]  host requests IP address: “DHCP request” msg  DHCP server sends address: “DHCP ack” msg

Network Layer 4-3 DHCP client-server scenario / / / DHCP server arriving DHCP client needs address in this network

Network Layer 4-4 DHCP server: arriving client DHCP discover src : , 68 dest.: ,67 yiaddr: transaction ID: 654 DHCP offer src: , 67 dest: , 68 yiaddr: transaction ID: 654 lifetime: 3600 secs DHCP request src: , 68 dest:: , 67 yiaddr: transaction ID: 655 lifetime: 3600 secs DHCP ACK src: , 67 dest: , 68 yiaddr: transaction ID: 655 lifetime: 3600 secs DHCP client-server scenario yiaddr = Your IP Address DHCP UDP IP Eth Phy

Network Layer 4-5 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 portion” versus host portion of address)

Network Layer 4-6 IP addresses: how to get one? Q: how does (sub)network get subnet part of IP addr? A: a (sub)network is allocated “portion of its provider ISP’s address space”  Subnetting Most ISP use “subnetting”  Allocate its address block into each sub group (organization)

Network Layer 4-7 Subnetting IP addresses are designed with two levels of hierarchy: A netid and a host id. This network ( /16) can have 2^16 hosts. There is only 1 network with so many hosts! /16

Network Layer 4-8 Subnetting

Network Layer 4-9 What if we break the network into 4 subnets? Subnetting /16  subnet 1: /18 subnet 2: /18 subnet 3: /18 subnet 4: /18

Network Layer 4-10 ISP's block /20 Organization /23 Organization /23 Organization /23... ….. …. …. Organization /23 Subnetting [Another Subnetting Example]

Network Layer 4-11 KoreaTech Subnetting KoreaTech is allocated the network address “ /19”  Each of 2 13 (=8192) hosts can have its IP address  Allocate its address block into each subnet! ISP's block /19 Organization /24 Organization /24 Organization /24... ….. …. …. Organization /

Network Layer 4-12 Subnetting - netmask (= )

Network Layer 4-13 r What is the subnetwork address if the address is and the subnet mask is ? m We apply the AND operation on the address and the subnet mask. Address ➡ Subnet Mask ➡ Subnetwork Address ➡ Or, Subnetting - netmask

Network Layer 4-14 Hierarchical addressing: route aggregation “Send me anything with addresses beginning /20” / / /23 Fly-By-Night-ISP Organization 0 Organization 7 Internet Organization 1 ISPs-R-Us “Send me anything with addresses beginning /16” /23 Organization hierarchical addressing allows efficient advertisement of routing information:

Network Layer 4-15 ISPs-R-Us has a more specific route to Organization 1 “Send me anything with addresses beginning /20” / / /23 Fly-By-Night-ISP Organization 0 Organization 7 Internet Organization 1 ISPs-R-Us “Send me anything with addresses beginning /16 or /23” /23 Organization Hierarchical addressing: more specific routes Remind: Longest Prefix Matching!

Network Layer 4-16 IP addressing: the last word... Q: how does an ISP get block of addresses? A: ICANN: Internet Corporation for Assigned Names and Numbers (  allocates addresses  manages (top-level) DNS  assigns domain names, resolves disputes

Network Layer 4-17 IP addressing: the last word...  ICANN 산하 IANA (Internet Assigned Numbers Authority)  인터넷 할당 번호 관리기관  RIR (Regional Internet Registry)  대륙별 인터넷 레지스트리  APNIC (Asia Pacific Network Information Center) 아시아 · 태평양 지역  RIPE-NCC (Réseaux IP Européens Network Co-ordination Centre) 유럽  ARIN (American Registry for Internet Number) 북남미 외 기타 지역  국가별 NIC (Network Information Center)  한국은 KISA( 한국인터넷진흥원 ) 안에 KRNIC( 한국인터넷정보센터 ) 에서 담당 

Network Layer 4-18 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 4-19 NAT: network address translation Addresses for private networks

Network Layer 4-20 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 network not explicitly addressable, visible by outside world (a security plus) NAT: network address translation

Network Layer 4-21 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 4-23  16-bit port-number field:  60,000 simultaneous connections with a single LAN-side address!  NAT is controversial:  routers should only process up to layer 3  violates end-to-end argument NAT possibility must be taken into account by app designers, e.g., P2P applications  address shortage should instead be solved by IPv6 NAT: network address translation

Network Layer 4-24 NAT traversal problem

Network Layer 4-25 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:  solution1: statically configure NAT to forward incoming connection requests at given port to server  e.g., ( , port 21) always forwarded to port NAT router client ?

Network Layer 4-26 NAT traversal problem  solution 2: Universal Plug and Play (UPnP)-Internet Gateway Device (IGD) Protocol. Allows NATed host to:  learn public IP address ( )  add/remove port mappings (with lease times) i.e., automate static NAT port map configuration NAT router IGD NAT translation table WAN side addr LAN side addr , , 80 ……

Network Layer 4-27 NAT traversal problem  solution 3: relaying (used in Skype, Kakao VoiceTalk)  NATed client establishes connection to relay  external client connects to relay  relay bridges packets between to connections client 1. connection to relay initiated by NATed host 2. connection to relay initiated by client 3. relaying established NAT router

Network Layer introduction 4.2 virtual circuit and datagram networks 4.3 what’s inside a router 4.4 IP: Internet Protocol  datagram format  IPv4 addressing  ICMP  IPv6 4.5 routing algorithms  link state  distance vector  hierarchical routing 4.6 routing in the Internet  RIP  OSPF  BGP 4.7 broadcast and multicast routing Chapter 4: outline

Network Layer 4-29 ICMP: internet control message protocol  ICMP Header format ICMP IP Eth Phy

Network Layer 4-30 ICMP: internet control message protocol  used by hosts & routers to communicate network- level information  error reporting: unreachable host, network, port, protocol  echo request/reply (used by ping)  network-layer “above” IP:  ICMP msgs carried in IP datagrams Type Code description 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest. host unreachable 3 2 dest. protocol unreachable 3 3 dest. port unreachable 3 6 dest. network unknown 3 7 dest. host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 router advertisement 10 0 router discovery 11 0 TTL expired 12 0 bad IP header

Network Layer 4-31 ICMP Ping

Network Layer 4-32 ICMP Ping - Request

Network Layer 4-33 ICMP Ping - Response

Network Layer 4-34 Traceroute and ICMP  source sends series of UDP segments to dest.  first set has TTL =1  second set has TTL=2, etc.  unlikely port number  when nth datagram arrives to nth router:  router discards datagrams  and sends source ICMP messages (type 11, code 0)  ICMP messages includes name of router & IP address  when ICMP messages arrives, source records RTTs  “Traceroute” does this 3 times stopping criteria:  UDP segment eventually arrives at destination host  destination returns ICMP “port unreachable” message (type 3, code 3)  source stops 3 probes

Network Layer 4-35 Dead Server Daemon and ICMP If Server process is down…  UDP segment eventually arrives at destination host  Destination returns ICMP “dest port unreachable” packet (type 3, code 3)  When source gets this ICMP, stops. application transport network link physical P1 application transport network link physical application transport network link physical P2 P3 P4 P1 host 1 host 2 host 3 Dead ICMP (Type=3, Code=3)

Network Layer introduction 4.2 virtual circuit and datagram networks 4.3 what’s inside a router 4.4 IP: Internet Protocol  datagram format  IPv4 addressing  ICMP  IPv6 4.5 routing algorithms  link state  distance vector  hierarchical routing 4.6 routing in the Internet  RIP  OSPF  BGP 4.7 broadcast and multicast routing Chapter 4: outline

What is IPv6? A next-generation version of IP (Internet Protocol), a basic Internet protocol, in which the number of IP addresses (numbers to identify terminals) is greatly increased. The current version of IP is version IP addresses (=approximately 4.3 billion) Number corresponding to one bucket full of sand. The next-generation of IP is version IP addresses Number corresponding to a mass of sand covering the whole world. 665,570,793,348,866,943,898,599 (or 6.65 x ) addresses for each square meter of the Earth's surface. Network Layer 4-37 IPv6: motivation

Network Layer 4-38 IPv6: motivation

Network Layer 4-39 IPv6: motivation  initial motivation: 32-bit address space soon to be completely allocated.  additional motivation:  header format helps speed processing/forwarding  header changes to facilitate QoS IPv6 datagram format:  fixed-length 40 byte header  no fragmentation allowed

0 bits31 VerIHLTotal Length IdentifierFlagsFragment Offset 32 bit Source Address 32 bit Destination Address Type of Service Options and Padding Time to LiveHeader ChecksumProtocol Removed 20 Octets + options : 13 fields, including 3 flag bits Changed IPv4 Header Format 한국기술교육대학교 40 IPv6 datagram format

40 Octets, 8 fields 031 Version Traffic Class Flow Label Payload LengthNext HeaderHop Limit 128 bit Source Address 128 bit Destination Address Changed 한국기술교육대학교 41 IPv6 Header Format IPv6 datagram format

Network Layer 4-42 IPv6 datagram format Priority (traffic class): identify priority among datagrams in a flow flow Label: identify datagrams in same “flow.” (concept of“flow” not well defined). next header: identify upper layer protocol for data data destination address (128 bits) source address (128 bits) payload len next hdr hop limit flow label pri ver 32 bits

Network Layer 4-43 Other changes from IPv4  checksum: removed entirely to reduce processing time at each hop  options: allowed, but outside of header, indicated by “Next Header” field  ICMPv6: new version of ICMP  additional message types, e.g. “Packet Too Big”  multicast group management functions

Network Layer 4-44 Transition from IPv4 to IPv6  not all routers can be upgraded simultaneously  no “flag days”  how will network operate with mixed IPv4 and IPv6 routers?  tunneling: IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers IPv4 source, dest addr IPv4 header fields IPv4 datagram IPv6 datagram IPv4 payload UDP/TCP payload IPv6 source dest addr IPv6 header fields

Network Layer 4-45 Tunneling physical view: IPv4 A B IPv6 E F C D logical view: IPv4 tunnel connecting IPv6 routers E IPv6 F A B

Network Layer 4-46 flow: X src: A dest: F data A-to-B: IPv6 Flow: X Src: A Dest: F data src:B dest: E B-to-C: IPv6 inside IPv4 E-to-F: IPv6 flow: X src: A dest: F data B-to-C: IPv6 inside IPv4 Flow: X Src: A Dest: F data src:B dest: E physical view: A B IPv6 E F C D logical view: IPv4 tunnel connecting IPv6 routers E IPv6 F A B Tunneling IPv4