1. Network Layer4-1 Today Collect homework New homework: Ch4 #16,19,21-24,26,27,29,31 (half graded, as usual) Due Wednesday Oct 15 in class Final programming project introduced in today’s lab

2. Network Layer4-2 Chapter 4 roadmap 4.1 Introduction and Network Service Models 4.2 Routing Principles 4.3 Hierarchical Routing 4.4 The Internet (IP) Protocol 4.5 Routing in the Internet 4.6 What’s Inside a Router? 4.7 IPv6 4.8 Multicast Routing 4.9 Mobility

3. Network Layer4-3 What is mobility? r spectrum of mobility, from the network perspective: no mobility high mobility 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.

4. Network Layer4-4 Mobility: Vocabulary Home network: permanent “home” of mobile (e.g., 128.119.40/24) Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 Home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network correspondent

5. Network Layer4-5 Mobility: more vocabulary Care-of-address: address in visited network. (e.g., 79.129.13.2) wide area network Visited network: network in which mobile currently resides (e.g., 79.129.13/24) Permanent address: remains constant ( e.g., 128.119.40.186) Foreign agent: entity in visited network that performs mobility functions on behalf of mobile. Correspondent: wants to communicate with mobile

6. Network Layer4-6 How do you contact a mobile friend: r search all phone books? r call her parents? r expect her to let you know where he/she is? I wonder where Alice moved to? Consider friend frequently changing addresses, how do you find her?

7. Network Layer4-7 Mobility: approaches r Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. m routing tables indicate where each mobile located m no changes to end-systems r Let end-systems handle it: m indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote m direct routing: correspondent gets foreign address of mobile, sends directly to mobile

8. Network Layer4-8 Mobility: approaches r Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. m routing tables indicate where each mobile located m no changes to end-systems r let end-systems handle it: m indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote m direct routing: correspondent gets foreign address of mobile, sends directly to mobile not scalable to millions of mobiles

9. Network Layer4-9 Mobility: registration End result: r Foreign agent knows about mobile r Home agent knows location of mobile wide area network home network visited network 1 mobile contacts foreign agent on entering visited network 2 foreign agent contacts home agent home: “this mobile is resident in my network”

10. Network Layer4-10 Mobility via Indirect Routing wide area network home network visited network 3 2 4 1 correspondent addresses packets using home address of mobile home agent intercepts packets, forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent

11. Network Layer4-11 Indirect Routing: comments r Mobile uses two addresses: m permanent address: used by correspondent (hence mobile location is transparent to correspondent) m care-of-address: used by home agent to forward datagrams to mobile r foreign agent functions may be done by mobile itself r triangle routing: correspondent-home-network- mobile m inefficient when correspondent, mobile are in same network

12. Network Layer4-12 Forwarding datagrams to remote mobile Permanent address: 128.119.40.186 Care-of address: 79.129.13.2 dest: 128.119.40.186 packet sent by correspondent dest: 79.129.13.2 dest: 128.119.40.186 packet sent by home agent to foreign agent: a packet within a packet dest: 128.119.40.186 foreign-agent-to-mobile packet

13. Network Layer4-13 Indirect Routing: moving between networks r suppose mobile user moves to another network m registers with new foreign agent m new foreign agent registers with home agent m home agent update care-of-address for mobile m packets continue to be forwarded to mobile (but with new care-of-address) r Mobility, changing foreign networks transparent: on going connections can be maintained!

14. Network Layer4-14 Mobility via Direct Routing wide area network home network visited network 4 2 4 1 correspondent requests, receives foreign address of mobile correspondent forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent 3

15. Network Layer4-15 Mobility via Direct Routing: comments r overcome triangle routing problem r non-transparent to correspondent: correspondent must get care-of-address from home agent m What happens if mobile changes networks?

16. Network Layer4-16 Mobile IP r RFC 3220 r has many features we’ve seen: m home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) r three components to standard: m agent discovery m registration with home agent m indirect routing of datagrams

17. Network Layer4-17 Mobile IP: agent discovery r agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) R bit: registration required H,F bits: home and/or foreign agent

18. Network Layer4-18 Mobile IP: registration example

19. Network Layer4-19 Network Layer: summary Next stop: the Data link layer! What we’ve covered: r network layer services r routing principles: link state and distance vector r hierarchical routing r IP r Internet routing protocols RIP, OSPF, BGP r what’s inside a router? r IPv6 r mobility

20. Network Layer4-20 Discussion Questions r TRUE or FALSE: m When a host joins a multicast group, it must change its IP address to be that of the multicast group it is joining. m In RPF, a node will receive multiple copies of the same packet. m In RPF, a node may forward multiple copies of a packet over the same outgoing link. r How can multicast apps learn the identities of the hosts that are participating in a multicast group? r How can the application be certain that only authorized recipients get the multicast data? r If 1000 multicast groups each choose a multicast group address at random, how likely is it that there will be conflicts?