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What we will cover…

What we will cover…. Home Networking: Network Address Translation (NAT) Mobile Routing. Home network. rest of Internet. local network (e.g., home network). NAT: Network Address Translation. rest of Internet. local network (e.g., home network) 10.0.0/24. 10.0.0.1. 10.0.0.4. 10.0.0.2.

dustin-allen
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What we will cover…

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  1. What we will cover… Home Networking: Network Address Translation (NAT)Mobile Routing

  2. Home network rest of Internet local network (e.g., home network)

  3. NAT: Network Address Translation rest of Internet local network (e.g., home network) 10.0.0/24 10.0.0.1 10.0.0.4 10.0.0.2 138.76.29.7 10.0.0.3 Datagrams with source or destination in this network have 10.0.0/24 address for source, destination (as usual) All datagrams leaving local network have same single source NAT IP address: 138.76.29.7, different source port numbers

  4. NAT: Network Address Translation • Advantages: • local network uses just one IP address as far as outside world is concerned: min. IP address wastage • can change addresses of devices in local network without notifying outside world: flexibility • devices inside local net not explicitly addressable, visible by outside world (a security plus).

  5. NAT: Network Address Translation 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

  6. 3 1 2 4 S: 10.0.0.1, 3345 D: 128.119.40.186, 80 S: 138.76.29.7, 5001 D: 128.119.40.186, 80 1: host 10.0.0.1 sends datagram to 128.119.40.186, 80 2: NAT router changes datagram source addr from 10.0.0.1, 3345 to 138.76.29.7, 5001, updates table S: 128.119.40.186, 80 D: 10.0.0.1, 3345 S: 128.119.40.186, 80 D: 138.76.29.7, 5001 NAT: Network Address Translation NAT translation table WAN side addr LAN side addr 138.76.29.7, 5001 10.0.0.1, 3345 …… …… 10.0.0.1 10.0.0.4 10.0.0.2 138.76.29.7 10.0.0.3 4: NAT router changes datagram dest addr from 138.76.29.7, 5001 to 10.0.0.1, 3345 3: Reply arrives dest. address: 138.76.29.7, 5001

  7. NAT: Network Address Translation • 16-bit port-number field: • 60,000 simultaneous connections with a single LAN-side address!

  8. NAT traversal problem • client wants to connect to server with address 10.0.0.1 • server address 10.0.0.1 local to LAN (client can’t use it as destination addr) • only one externally visible NATted address: 138.76.29.7 • solution 1: statically configure NAT to forward incoming connection requests at given port to server • e.g., (123.76.29.7, port 2500) always forwarded to 10.0.0.1 10.0.0.1 Client ? 10.0.0.4 138.76.29.7 NAT router

  9. 10.0.0.1 NAT router NAT traversal problem • solution 2: relaying (used in Skype) • NATed client establishes connection to relay • External client connects to relay • relay bridges packets between connections 2. connection to relay initiated by client 1. connection to relay initiated by NATted host 3. relaying established Client 138.76.29.7

  10. NAT: Network Address Translation • NAT is controversial: • routers should only process up to layer 3 • NAT breaks that protocol!!!

  11. Mobile Routing

  12. no mobility high mobility What is mobility? • spectrum of mobility, from thenetwork perspective: mobile user, using same access point mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) mobile user, connecting/ disconnecting from network using DHCP.

  13. Mobility: Vocabulary home network: permanent “home” of mobile (e.g., 128.119.40/24) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 correspondent

  14. Mobility: more vocabulary visited network: network in which mobile currently resides (e.g., 79.129.13/24) Permanent address: remains constant (e.g., 128.119.40.186) Care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network home agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile

  15. Mobility: approaches • Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. • routing tables indicate where each mobile located • no changes to end-systems • Let end-systems handle it: • indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote • direct routing: correspondent gets foreign address of mobile, sends directly to mobile

  16. Mobility: approaches • Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. • routing tables indicate where each mobile located • no changes to end-systems • let end-systems handle it: • indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote • direct routing: correspondent gets foreign address of mobile, sends directly to mobile not scalable to millions of mobiles

  17. mobile contacts foreign agent on entering visited network foreign agent contacts home agent home: “this mobile is resident in my network” 1 2 Mobility: registration visited network home network End result: • Foreign agent knows about mobile • Home agent knows location of mobile wide area network

  18. foreign agent receives packets, forwards to mobile home agent intercepts packets, forwards to foreign agent correspondent addresses packets using home address of mobile mobile replies directly to correspondent 3 2 4 1 Mobility via Indirect Routing visited network home network wide area network

  19. foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet dest: 128.119.40.186 dest: 128.119.40.186 dest: 128.119.40.186 packet sent by correspondent dest: 79.129.13.2 Forwarding datagrams to remote mobile Permanent address: 128.119.40.186 Care-of address: 79.129.13.2

  20. Indirect Routing: comments • Mobile uses two addresses: • permanent address: used by correspondent (hence mobile location is transparent to correspondent) • care-of-address: used by home agent to forward datagrams to mobile • foreign agent functions may be done by mobile itself • triangle routing: correspondent-home-network-mobile • inefficient when correspondent, mobile are in same network

  21. foreign agent receives packets, forwards to mobile mobile replies directly to correspondent 4 2 4 1 3 Mobility via Direct Routing correspondent forwards to foreign agent visited network home network wide area network correspondent requests, receives foreign address of mobile

  22. Mobility via Direct Routing: comments • overcome triangle routing problem • non-transparent to correspondent: correspondent must get care-of-address from home agent • What happens if mobile changes networks?

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