16: IP Extensions – VPN, Mobile IP, IP Multicast

1. 16: IP Extensions – VPN, Mobile IP, IP Multicast Last Modified: 10/23/2014 6:19:03 PM Adapted from Gordon Chaffee’s slides http://bmrc.berkeley.edu/people/chaffee/advnet98/ 4: Network Layer

2. Virtual Private Networks (VPN) 4: Network Layer

3. Virtual Private Networks • Definition • A VPN is a private network constructed within the public Internet • Goals • Connect private networks using shared public infrastructure • Examples • Connect two sites of a business • Allow people working at home to have full access to company network 4: Network Layer

4. How accomplished? • IP encapsulation and tunneling • Router at one end of tunnel places private IP packets into the data field of new IP packets (could be encrypted first for security) which are unicast to the other end of the tunnel 4: Network Layer

5. Tunneling IPv6 inside IPv4 where needed 4: Network Layer

6. Motivations • Economic • Using shared infrastructure lowers cost of networking • Less of a need for leased line connections • Communications privacy • Communications can be encrypted if required • Ensure that third parties cannot use virtual network • Virtualized equipment locations • Hosts on same network do not need to be co-located • Make one logical network out of separate physical networks • Support for private network features • Multicast, protocols like IPX or Appletalk, etc 4: Network Layer

7. Examples • Logical Network Creation • Virtual Dial-Up 4: Network Layer

8. Logical Network Creation Example Network 1 • Remote networks 1 and 2 create a logical network • Secure communication at lowest level Gateway Tunnel Gateway Internet Network 2 4: Network Layer

9. Virtual Dial-up Example • Worker dials ISP to get basic IP service • Worker creates tunnel to Home Network Public Switched Telephone Network (PSTN) Internet Service Provider Gateway Gateway Tunnel Internet Home Network Worker Machine 4: Network Layer

10. MobileIP 4: Network Layer

11. MobileIP • Goal: Allow machines to roam around and maintain IP connectivity • Problem: IP addresses => location • This is important for efficient routing • Solutions? • DHCP? • ok for relocation but not for ongoing connections • Dynamic DNS (mobile nodes update name to IP address mapping as they move around)? • ok for relocation but not for ongoing connections 4: Network Layer

12. Mobile IP • Allows computer to roam and be reachable • Basic architecture • Home agent (HA) on home network • Foreign agent (FA) at remote network location • Home and foreign agents tunnel traffic • Non-optimal data flow 4: Network Layer

13. MobileIP • Mobile nodes have a permanent home address and a default local router called the “home agent” • The router nearest a nodes current location is called the “foreign agent” • Register with foreign agent when connect to network • Located much like the DHCP server 4: Network Layer

14. Forwarding Packets • Home agent impersonates the mobile host by changing the mapping from IP address to hardware address (“proxy ARP”) • Sends any packets destined for mobile host on to the foreign agent with IP encapsulation • Foreign agent strips off and does a special translation of the mobile nodes IP address to its current hardware address 4: Network Layer

15. 1. The Mobile Node registers itself with the Foreign Agent on the Foreign Subnet. The Foreign Agent opens an IP-IP tunnel to the Home Agent. The Home Agent begins listening for packets sent to 169.229.2.98. Register 2. The Fixed Node initiates a connection to the Mobile Node. It sends packets to the Mobile Node’s home IP address, 169.229.2.98. The packets are routed to the Home Subnet. 3. The Home Agent receives them, encapsulates them in IP-IP packets, and it sends them to the Foreign Agent. Encapsulated packets are addressed to 18.86.0.253. 4. The Foreign Agent decapsulates the IP-IP packets, and it sends them out on the Foreign Subnet. These packets will be addressed to 169.229.2.98. 5. The Mobile Node receives the packets, and it sends responses directly to the Fixed Node at 128.95.4.112. Mobile IP Example Foreign Agent Mobile Node 169.229.2.98 18.86.0.253 Foreign Subnet Fixed Node Internet 128.95.4.112 Home Subnet Home Agent 169.229.2.97 4: Network Layer

16. Avoiding the Foreign Agent • Mobile host can also obtain a new IP address on the remote network and inform the home agent • The home agent can then resend the packet to the new IP address 4: Network Layer

17. Optimizations • What if two remote hosts are temporarily close together • If they want to send traffic to each other, why should it have to go all the way to their home agents and back again • Optimizations exist to allow the sending node to learn and cache the current location of a recipient to avoid this problem 4: Network Layer

18. IP Multicast 4: Network Layer

19. What is multicast? • 1 to N communication • Bandwidth-conserving technology that reduces traffic by simultaneously delivering a single stream of information to multiple recipients • Examples of Multicast • Network hardware efficiently supports multicast transport • Example: Ethernet allows one packet to be received by many hosts • Many different protocols and service models • Examples: IETF IP Multicast, ATM Multipoint 4: Network Layer

20. Unicast • Problem • Sending same data to many receivers via unicast is inefficient • Example • Popular WWW sites become serious bottlenecks • Especially bad for audio/video streams Sender R 4: Network Layer

21. Multicast • Efficient one to many data distribution Sender R 4: Network Layer

22. IP Multicast Introduction • Efficient one to many data distribution • Tree style data distribution • Packets traverse network links only once • Location independent addressing • IP address per multicast group • Receiver oriented service model • Applications can join and leave multicast groups • Senders do not know who is listening • Similar to television model • Contrasts with telephone network, ATM 4: Network Layer

23. IP Multicast • Service • All senders send at the same time to the same group • Receivers subscribe to any group • Routers find receivers • Unreliable delivery • Reserved IP addresses • 224.0.0.0 to 239.255.255.255 reserved for multicast • Static addresses for popular services (e.g. Session Announcement Protocol) 4: Network Layer

24. Internet Group Management Protocol (IGMP) • Protocol for managing group membership • IP hosts report multicast group memberships to neighboring routers • Messages in IGMPv2 (RFC 2236) • Membership Query (from routers) • Membership Report (from hosts) • Leave Group (from hosts) • Announce-Listen protocol with Suppression • Hosts respond only if no other hosts has responded • Soft State protocol 4: Network Layer

25. 3 IGMP Example (1) • Host 1 begins sending packets • No IGMP messages sent • Packets remain on Network 1 • Router periodically sends IGMP Membership Query 1 Network 1 Network 2 Router 4 2 4: Network Layer

26. Leave Group Membership Report 3 3 3 3 IGMP Example (2) 1 • Host 3 joins conference • Sends IGMP Membership Report message • Router begins forwarding packets onto Network 2 • Host 3 leaves conference • Sends IGMP Leave Group message • Only sent if it was the last host to send an IGMP Membership Report message Network 1 Network 2 Router 4 2 4: Network Layer

27. Source Specific Filtering: IGMPv3 • Adds Source Filtering to group selection • Receive packets only from specific source addresses • Receive packets from all but specific source addresses • Benefits • Helps prevent denial of service attacks • Better use of bandwidth • Status: Internet Draft? 4: Network Layer

28. Multicast Routing Discussion • What is the problem? • Need to find all receivers in a multicast group • Need to create spanning tree of receivers • Design goals • Minimize unwanted traffic • Minimize router state • Scalability • Reliability 4: Network Layer

29. Data Flooding • Send data to all nodes in network • Problem • Need to prevent cycles • Need to send only once to all nodes in network • Could keep track of every packet and check if it had previously visited node, but means too much state R2 R1 R3 Sender 4: Network Layer

30. Reverse Path Forwarding (RPF) • Simple technique for building trees • Send out all interfaces except the one with the shortest path to the sender • In unicast routing, routers send to the destination via the shortest path • In multicast routing, routers send away from the shortest path to the sender 4: Network Layer

31. 1.Router R1 checks: Did the data packet arrive on the interface with the shortest path to the Sender? Yes, so it accepts the packet, duplicates it, and forwards the packet out all other interfaces except the interface that is the shortest path to the sender (i.e the interface the packet arrived on). 2.Router R2 accepts packets sent from Router R1 because that is the shortest path to the Sender. The packet gets sent out all interfaces. Drop 3.Router R2 drops packets that arrive from Router R3 because that is not the shortest path to the sender. Avoids cycles. Drop Reverse Path Forwarding Example Sender R1 R2 R3 R4 R5 R6 R7 4: Network Layer

32. Multicast Tunneling • Problem • Not all routers are multicast capable • Want to connect domains with non-multicast routers between them • Solution • Encapsulate multicast packets in unicast packet • Tunnel multicast traffic across non-multicast routers • We will see more examples of tunneling later 4: Network Layer

33. Multicast Tunneling Example (1) Multicast Router 2 decapsulates IP-in-IP packets. It then forwards them using Reverse Path Multicast. Multicast Router 1 encapsulates multicast packets for groups that have receivers outside of network 1. It encapsulates them as unicast IP-in-IP packets. Encapsulated Data Packet Multicast Router 2 UR1 UR2 Multicast Router 1 Unicast Routers Sender 1 Receiver Network 2 Network 1 4: Network Layer

34. Multicast Tunneling Example (2) Virtual Network Topology MR1 MR2 Virtual Interfaces 4: Network Layer

35. Roadmap • Finished with the network layer and IP specifics • Next on to the link layer • If two hosts are on the same network how do they send data directly to one another 4: Network Layer

36. Outtakes 4: Network Layer

37. Protocol Independent Multicast (PIM) • Uses unicast routing table for topology • Dense mode (PIM-DM) • For groups with many receivers in local/global region • Like DVMRP, a flood and prune algorithm • Sparse mode (PIM-SM) • For groups with few widely distributed receivers • Builds shared tree per group, but may construct source rooted tree for efficiency • Explicit join 4: Network Layer

38. MBone • MBONE • Multicast capable virtual network, subset of Internet • Native multicast regions connection with tunnels • In 1992, the MBone was created to further the development of IP multicast • Experimental, global multicast network • Served as a testbed for multicast applications development • vat -- audio tool • vic -- video tool • wb -- shared whiteboard 4: Network Layer

39. Data Distribution Choices • Source rooted trees • State in routers for each sender • Forms shortest path tree from each sender to receivers • Minimal delays from sources to destinations • Shared trees • All senders use the same distribution tree • State in routers only for wanted groups • No per sender state (until IGMPv3) • Greater latency for data distribution 4: Network Layer

40. Often does not use optimal path from source to destination. Routers maintain state for each sender in a group. Traffic is heavily concentrated on some links while others get little utilization. Source Rooted vs Shared Trees A A B C B C D D Shared Tree Source Rooted Trees 4: Network Layer

41. Distance Vector Multicast Routing (DVMRP) • Steve Deering, 1988 • Source rooted spanning trees • Shortest path tree • Minimal hops (latency) from source to receivers • Extends basic distance vector routing • Flood and prune algorithm • Initial data sent to all nodes in network(!) using Reverse Path Forwarding • Prunes remove unwanted branches • State in routers for all unwanted groups • Periodic flooding since prune state times out (soft state) 4: Network Layer

42. DVMRP Algorithm • Truncated Reverse Path Multicast • Optimized version of Reverse Path Forwarding • Truncating • No packets sent onto leaf networks with no receivers • Still how “truncated” is this? • Pruning • Prune messages sent if no downstream receivers • State maintained for each unwanted group • Grafting • On join or graft, remove prune state and propagate graft message 4: Network Layer

43. Protocol Independent Multicast (PIM) • Uses unicast routing table for topology • Dense mode (PIM-DM) • For groups with many receivers in local/global region • Like DVMRP, a flood and prune algorithm • Sparse mode (PIM-SM) • For groups with few widely distributed receivers • Builds shared tree per group, but may construct source rooted tree for efficiency • Explicit join 4: Network Layer

44. IP Multicast in the Real World 4: Network Layer

45. Commercial Motivation • Problem • Traffic on Internet is growing about 100% per year • Router technology is getting better at 70% per year • Routers that are fast enough are very expensive • ISPs need to find ways to reduce traffic • Multicast could be used to… • WWW: Distribute data from popular sites to caches throughout Internet • Send video/audio streams multicast • Software distribution 4: Network Layer

46. ISP Concerns • Multicast causes high network utilization • One source can produce high total network load • Experimental multicast applications are relatively high bandwidth: audio and video • Flow control non-existent in many multicast apps • Multicast breaks telco/ISP pricing model • Currently, both sender and receiver pay for bandwidth • Multicast allows sender to buy less bandwidth while reaching same number of receivers • Load on ISP network not proportional to source data rate 4: Network Layer

47. Economics of Multicast • One packet sent to multiple receivers • Sender + Benefits by reducing network load compared to unicast + Lower cost of network connectivity • Network service provider - One packet sent can cause load greater than unicast packet load + Reduces overall traffic that flows over network • Receiver = Same number of packets received as unicast 4: Network Layer

48. Multicast Problems • Multicast is immature • Immature protocols and applications • Tools are poor, difficult to use, debugging is difficult • Routing protocols leave many issues unresolved • Interoperability of flood and prune/explicit join • Routing instability • Multicast development has focused on academic problems, not business concerns • Multicast breaks telco/ISP traffic charging and management models • Routing did not address policy • PIM, DVMRP, CBT do not address ISP policy concerns • BGMP addresses some ISP concerns, but it is still under development 4: Network Layer

49. Current ISP Multicast Solution • Restrict senders of multicast data • Charge senders to distribute multicast traffic • Static agreements • Do not forward multicast traffic • Some ISP’s offer multicast service to customers (e.g. UUNET UUCast) • ISP beginning to discuss peer agreements 4: Network Layer

50. Distance Vector Multicast Routing (DVMRP) • Steve Deering, 1988 • Source rooted spanning trees • Shortest path tree • Minimal hops (latency) from source to receivers • Extends basic distance vector routing • Flood and prune algorithm • Initial data sent to all nodes in network(!) using Reverse Path Forwarding • Prunes remove unwanted branches • State in routers for all unwanted groups • Periodic flooding since prune state times out (soft state) 4: Network Layer