CPSC Network Layer4-1 IP addresses: how to get one? Q: How does a host get IP address? r hard-coded by system admin in a file m Windows: control-panel->network->configuration- >tcp/ip->properties m UNIX: /etc/rc.config r DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server m “plug-and-play”

CPSC Network Layer4-2 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 an “on”) Support for mobile users who want to join network (more shortly) DHCP overview: m host broadcasts “DHCP discover” msg m DHCP server responds with “DHCP offer” msg m host requests IP address: “DHCP request” msg m DHCP server sends address: “DHCP ack” msg

CPSC Network Layer4-3 DHCP client-server scenario A B E DHCP server arriving DHCP client needs address in this network

CPSC Network Layer4-4 DHCP client-server scenario DHCP server: arriving client time 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

CPSC Network Layer4-5 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

CPSC Network Layer4-6 NAT: Network Address Translation r Motivation: local network uses just one IP address as far as outside world is concerned: m range of addresses not needed from ISP: just one IP address for all devices m can change addresses of devices in local network without notifying outside world m can change ISP without changing addresses of devices in local network m devices inside local net not explicitly addressable, visible by outside world (a security plus).

CPSC Network Layer4-7 NAT: Network Address Translation Implementation: NAT router must: m 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. m remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair m 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

CPSC Network Layer4-8 NAT: Network Address Translation 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

CPSC Network Layer4-9 NAT: Network Address Translation r 16-bit port-number field: m 60,000 simultaneous connections with a single LAN-side address! r NAT is controversial: m routers should only process up to layer 3 m violates end-to-end argument NAT possibility must be taken into account by app designers, eg, P2P applications m address shortage should instead be solved by IPv6

CPSC Network Layer4-10 NAT traversal problem r client wants to connect to server with address m server address local to LAN (client can’t use it as destination addr) m only one externally visible NATted address: r solution 1: statically configure NAT to forward incoming connection requests at given port to server m e.g., ( , port 2500) always forwarded to port NAT router Client ?

CPSC Network Layer4-11 NAT traversal problem r solution 2: Universal Plug and Play (UPnP) Internet Gateway Device (IGD) Protocol. Allows NATted host to:  learn public IP address ( )  add/remove port mappings (with lease times) i.e., automate static NAT port map configuration NAT router IGD

CPSC Network Layer4-12 NAT traversal problem r solution 3: relaying (used in Skype) m NATed client establishes connection to relay m External client connects to relay m relay bridges packets between to connections Client NAT router 1. connection to relay initiated by NATted host 2. connection to relay initiated by client 3. relaying established

CPSC Network Layer4-13 Chapter 4: Network Layer r 4. 1 Introduction r 4.2 Virtual circuit and datagram networks r 4.3 What’s inside a router r 4.4 IP: Internet Protocol m Datagram format m IPv4 addressing m ICMP m IPv6 r 4.5 Routing algorithms m Link state m Distance Vector m Hierarchical routing r 4.6 Routing in the Internet m RIP m OSPF m BGP r 4.7 Broadcast and multicast routing

CPSC Network Layer4-14 IPv6 r Initial motivation: 32-bit address space soon to be completely allocated. r Additional motivation: m header format helps speed processing/forwarding m header changes to facilitate QoS IPv6 datagram format: m fixed-length 40 byte header m no fragmentation allowed

CPSC Network Layer4-15 IPv6 Header (Cont) Priority: identify priority among datagrams in flow Flow Label: identify datagrams in same “flow.” (concept of“flow” not well defined). Next header: identify upper layer protocol for data

CPSC Network Layer4-16 Other Changes from IPv4 r Checksum: removed entirely to reduce processing time at each hop r Options: allowed, but outside of header, indicated by “Next Header” field r ICMPv6: new version of ICMP m additional message types, e.g. “Packet Too Big” m multicast group management functions

CPSC Network Layer4-17 Transition From IPv4 To IPv6 r Not all routers can be upgraded simultaneous m no “flag days” m How will the network operate with mixed IPv4 and IPv6 routers? r Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers

CPSC Network Layer4-18 Tunneling A B E F IPv6 tunnel Logical view: Physical view: A B E F IPv6 IPv4

CPSC Network Layer4-19 Tunneling A B E F IPv6 tunnel Logical view: Physical view: A B E F IPv6 C D IPv4 Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data Src:B Dest: E Flow: X Src: A Dest: F data Src:B Dest: E A-to-B: IPv6 E-to-F: IPv6 B-to-C: IPv6 inside IPv4 B-to-C: IPv6 inside IPv4