4: Network Layer 4a-1 16: IP Extensions – VPN, Mobile IP, IP Multicast Last Modified: 11/22/ :04:45 PM Adapted from Gordon Chaffee’s slides

4: Network Layer 4a-2 Virtual Private Networks (VPN)

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

4: Network Layer 4a-4 How accomplished? r IP encapsulation and tunneling r 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 4a-5 Tunneling IPv6 inside IPv4 where needed

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

4: Network Layer 4a-7 Examples r Logical Network Creation r Virtual Dial-Up

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

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

4: Network Layer 4a-10 MobileIP

4: Network Layer 4a-11 MobileIP r Goal: Allow machines to roam around and maintain IP connectivity r Problem: IP addresses => location m This is important for efficient routing r Solutions? m DHCP? ok for relocation but not for ongoing connections m 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 4a-12 Mobile IP r Allows computer to roam and be reachable r Basic architecture m Home agent (HA) on home network m Foreign agent (FA) at remote network location m Home and foreign agents tunnel traffic m Non-optimal data flow

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

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

4: Network Layer 4a-15 Mobile IP Example Home Agent Foreign Agent Internet Foreign Subnet Home Subnet Mobile Node Fixed Node Register 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 The Fixed Node initiates a connection to the Mobile Node. It sends packets to the Mobile Node’s home IP address, The packets are routed to the Home Subnet. 4. The Foreign Agent decapsulates the IP-IP packets, and it sends them out on the Foreign Subnet. These packets will be addressed to The Mobile Node receives the packets, and it sends responses directly to the Fixed Node at The Home Agent receives them, encapsulates them in IP-IP packets, and it sends them to the Foreign Agent. Encapsulated packets are addressed to

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

4: Network Layer 4a-17 Optimizations r What if two remote hosts are temporarily close together r 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 r Optimizations exist to allow the sending node to learn and cache the current location of a recipient to avoid this problem

4: Network Layer 4a-18 IP Multicast

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

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

4: Network Layer 4a-21 Multicast R Sender r Efficient one to many data distribution

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

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

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

4: Network Layer 4a-25 IGMP Example (1) Network 1 r Host 1 begins sending packets m No IGMP messages sent m Packets remain on Network 1 r Router periodically sends IGMP Membership Query Network 2 Router

4: Network Layer 4a-26 IGMP Example (2) Network 1 r Host 3 joins conference m Sends IGMP Membership Report message r Router begins forwarding packets onto Network 2 r Host 3 leaves conference m Sends IGMP Leave Group message m Only sent if it was the last host to send an IGMP Membership Report message Network 2 Router Membership Report 33 Leave Group

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

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

4: Network Layer 4a-29 Data Flooding r Send data to all nodes in network r Problem m Need to prevent cycles m Need to send only once to all nodes in network m Could keep track of every packet and check if it had previously visited node, but means too much state Sender R3R1 R2

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

4: Network Layer 4a-31 Reverse Path Forwarding Example R5R6 R3R2 R1 R4R7 Sender 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. 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). Drop 3. Router R2 drops packets that arrive from Router R3 because that is not the shortest path to the sender. Avoids cycles.

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

4: Network Layer 4a-33 Multicast Tunneling Example (1) UR1UR2 Multicast Router 1 Multicast Router 2 Sender 1 Encapsulated Data Packet Unicast Routers Multicast Router 1 encapsulates multicast packets for groups that have receivers outside of network 1. It encapsulates them as unicast IP-in-IP packets. Network 1 Receiver Network 2 Multicast Router 2 decapsulates IP-in-IP packets. It then forwards them using Reverse Path Multicast.

4: Network Layer 4a-34 Multicast Tunneling Example (2) MR1MR2 Virtual Interfaces Virtual Network Topology

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

4: Network Layer 4a-36 Outtakes

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

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

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

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

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

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

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

4: Network Layer 4a-44 IP Multicast in the Real World

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

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

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

4: Network Layer 4a-48 Multicast Problems r Multicast is immature m Immature protocols and applications m Tools are poor, difficult to use, debugging is difficult m Routing protocols leave many issues unresolved Interoperability of flood and prune/explicit join Routing instability r Multicast development has focused on academic problems, not business concerns m Multicast breaks telco/ISP traffic charging and management models m 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 4a-49 Current ISP Multicast Solution r Restrict senders of multicast data r Charge senders to distribute multicast traffic m Static agreements r Do not forward multicast traffic m Some ISP’s offer multicast service to customers (e.g. UUNET UUCast) m ISP beginning to discuss peer agreements

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

4: Network Layer 4a-51 DVMRP Algorithm r Truncated Reverse Path Multicast m Optimized version of Reverse Path Forwarding m Truncating No packets sent onto leaf networks with no receivers m Still how “truncated” is this? r Pruning m Prune messages sent if no downstream receivers m State maintained for each unwanted group r Grafting m On join or graft, remove prune state and propagate graft message

4: Network Layer 4a-52 Truncated Reverse Path Multicast Example R5R6 R3R2 R1 R4R7 Sender Router R2 accepts packets sent from Router R1 because that is the shortest path to the Sender. Unlike Reverse Path Forwarding, which simply forwards out all but the incoming interface, DVMRP’s Reverse Path Multicast maintains a list of child links for each sender. It sends packets only out child links, not parent or sibling links. This means Router R2 will not forward data from the Sender to Router R3. Siblings Receiver Truncation: no packets forwarded onto leaf networks with no receivers

4: Network Layer 4a-53 DVMRP Pruning Example R5R6 R3R2 R1 R4R7 Sender Receiver Prune

4: Network Layer 4a-54 DVMRP Grafting Example R5R6 R3R2 R1 R4R7 Sender Receiver 1 Membership Report Receiver 2 Receiver 2 joins multicast group Join from Receiver 2 causes router to remove its prune state and send a Join message up toward the Sender. Graft Prune State Graft

4: Network Layer 4a-55 DVMRP Problems r State maintained for unwanted groups r Bandwidth intensive m Periodic data flooding per group No explicit joins, and prune state times out m Not suitable for heterogeneous networks r Poorly handles large number of senders m Scaling = O(Senders, Groups) r Problems of distance vector routing m slow convergence m cycles due to lack of global knowledge

4: Network Layer 4a-56 Core Based Trees (CBT) r Attributes m Single shared tree per group => sparse trees m Large number of senders m Routing tables scale well, size = O(Groups) m Bi-directional tree

4: Network Layer 4a-57 Group Management in CBT R1RR2R3 RR R Receiver 1 Join 1. Receiver 1 joins the multicast group, causing Router R2 to join the shared tree by sending a Join message toward the Core. The Core sends an explicit ACK back to to Router R2. R R4 R Core Receiver 2 Ack Join Ack 2. Receiver 2 also joins the multicast group, causing Router R3 to join the shared tree by sending a Join message toward the Core. Router R4 is already part of the shared tree, so it adds R3 to the shared tree and sends back an ACK.

4: Network Layer 4a-58 Sending Data in CBT (1) R1RR2R3 RR R Receiver 1 Packets from the Sender are propagated by routers on the shared tree by sending out all interfaces that are branches of the tree except the interface the packet arrived on. R5 R4 R Core Receiver 2 Sender Case 1: Sender is a member of the multicast group, and the first hop router is on the shared tree.

4: Network Layer 4a-59 Sending Data in CBT (2) R1RR2R3 RR R Receiver 1. Router R1 is not on the shared tree, so it does an IP-in-IP encapsulation of packets from the Sender, and it unicasts the encapsulated packets to the Core. R5 R4 R Core Receiver Case 2: Sender is not a member of the multicast group, and the first hop router is not on the shared tree. Sender Encapsulated Data Packet 2. The Core decapsulates the encapsulated packets, and it distributes them out the shared tree.

4: Network Layer 4a-60 Protocol Independent Multicast (PIM) r Uses unicast routing table for topology r Dense mode (PIM-DM) m For groups with many receivers in local/global region m Like DVMRP, a flood and prune algorithm r Sparse mode (PIM-SM) m For groups with few widely distributed receivers m Builds shared tree per group, but may construct source rooted tree for efficiency m Explicit join

4: Network Layer 4a-61 PIM Sparse Mode r Hybrid protocol that combines features of DVMRP and CBT r Suited to widely distributed, heterogeneous networks r Shared tree centered at Rendezvous Point (RP) r Shared tree introduces sources to receivers r Source specific trees for heavy traffic flows r Unidirectional distribution tree

4: Network Layer 4a-62 Group Management in PIM-SM DR1RDR2R RR R Receiver 1 Rendezvous Point 1. Receiver 1 joins the multicast group. Designated Router DR2 sends a Join message toward the RP. Periodically, DR2 resends the Join message in case it was lost. Join 2. Routers along the path to RP create router state for the group, adding themselves to the shared tree. R R R RP Join

4: Network Layer 4a-63 Sending Data in PIM-SM DR1RDR2R R Receiver 1 Rendezvous Point (RP) 1. Sender 1 begins sending to a multicast group. 2. Designated Router DR1 encapsulates the packets from Sender 1 in Register messages and unicasts them to RP. 3. The RP decapsulates the packet and sends it out the shared tree. Encapsulated Data Packet R R RP Sender 1 DR R R

4: Network Layer 4a-64 PIM-SM Source Specific Bypass DR1R3DR2R R Receiver 1 Rendezvous Point (RP) 1. Designated Router DR2 sees traffic from Sender 1 at a rate > threshold. It sends a source specific join request toward Sender 1. Encapsulated Data Packet R R RP Sender 1 DR R R Source Specific Join 2. The join request reaches DR1, and DR1 adds DR2 to the source specific tree for Sender 1. Data from Sender 1 begins flowing on the source specific tree to DR2. 3. When DR2 sees traffic from Sender 1 coming from R3, it sends a Source Specific Prune message toward RP. This removes DR2 from the shared tree. Source Specific Prune

4: Network Layer 4a-65 RP Joins Source Specific Tree DR1RDR2R R Receiver 1 1. RP sees traffic from Sender 1 at a rate > threshold. It sends source specific join request toward Sender 1. Encapsulated Data Packet R R RP Sender 1 DR R R Source Specific Join 3. When RP sees unencapsulated traffic from Sender 1, it sends a Register Stop message to DR1. DR1 then stops sending encapsulated traffic to RP. Source Specific Join 2. The join request reaches DR1, and DR1 adds RP to the source specific tree for Sender 1. Data from Sender 1 begins flowing on the source specific tree to RP.

4: Network Layer 4a-66 Problems with PIM r Global broadcasts of all Rendezvous Points r Sensitive to location of RP r No administrative control over multicast traffic; policy controls lacking r Conceived as inter-domain, but now considered intra-domain

4: Network Layer 4a-67 Classification of Tree Building Choices r Flood network topology to all routers m Link state protocol m Multicast Extensions to OSPF (MOSPF) r Flood and prune m Distance Vector Multicast Routing Protocol (DVMRP) m Protocol Independent Multicast Dense Mode (PIM-DM) r Explicit join m Core Based Trees (CBT) m Protocol Independent Multicast Sparse Mode (PIM-SM)

4: Network Layer 4a-68 Border Gateway Multicast Protocol (BGMP) r Administrative control of multicast traffic r Hierarchical multicast address allocation r Uses BGP for routing tables r No global broadcasts of anything r Bi-directional shared multicast routing tree