NP - Unit 4 - Routing - RIP, OSPF and Internet Multicasting
- 1. UNIT - IV ROUTING–RIP, OSPF AND INTERNET MULTICASTING
- 2. Static & Dynamic Interior Routes • Two routers within an autonomous system are said to be interior to one another. • How can routers in an autonomous system learn about networks within the autonomous system? • The manager keeps a list of networks and updates the forwarding tables whenever a new network is added to, or deleted from, the autonomous system. • The disadvantages of a manual system are obvious.
- 3. Example
- 4. • To automate the task of keeping routing information accurate, interior routers periodically communicate with one another to exchange routing information. • BGP-Border Gateway Protocol • Diversity • the network topologies, sizes, and network technologies vary widely. • interior routing protocols • If protocol A is used on some routers and protocol B is used on other routers, at least one router between the two sets must communicate using both protocols and must have a way to transfer information between them. • Interior Gateway Protocol (IGP)
- 5. Routing Information Protocol (RIP) • Routing Information Protocol (RIP) is a distance-vector routing protocol. • Routers running the distance-vector protocol send all or a portion of their routing tables in routing-update messages to their neighbors. • RIP relies on physical network broadcast to make routing exchanges quickly .
- 6. RIP operation • RIP supports two type of participants: active and passive. • Active participants advertise their routes to others; passive participants listen to RIP messages and use them to update their forwarding table, but do not advertise. • Only a router can run RIP in active mode; if a host runs RIP, the host must use passive mode. • A router running RIP in active mode broadcasts a routing update message every 30 seconds. • Each update contains a set of pairs, where each pair specifies an IP network address and an integer distance to that network. • RIP uses a hop count metric to measure distances.
- 7. • The number of hops or the hop count along a path from a given source to a given destination refers to the number of networks that a datagram encounters along that path. • What happens if a router fails (e.g., the router crashes)? • RIP specifies that when a router receives and installs a route in its forwarding table, the router must start a timer for the entry. • The timer is reset whenever the router receives another RIP message advertising the same route. The route becomes invalid if 180 seconds pass without the route being advertised again. • RIP must handle three kinds of errors: • the algorithm does not explicitly detect forwarding loops, RIP must either assume participants can be trusted or take precautions to prevent such loops. • low value for the maximum possible distance • slow convergence or count to infinity in which inconsistencies arise because routing update messages propagate slowly across the network.
- 8. Slow Convergence Problem • In part (a), we assume all routers are running a distance-vector protocol. • In part (b) of the figure, we assume a failure has occurred and disconnected R1 from network 1. • part (c) of the figure shows what has happened:R1 has installed a route for network 1that goes through R2, and R2 has a route that goes through R1.
- 9. Solving the Slow Convergence Problem – 3 solutions • split horizon update - allows distance vector protocols, such as RIP, to solve the slow convergence problem. • a router does not propagate information about a route back over the same interface from which the route arrived. no forwarding loop appears. • Hold down forces a participating router to ignore information about a network for a fixed period of time following receipt of a message that claims the network is unreachable. • The disadvantage of a hold down technique is that if forwarding loops occur, they will be preserved for the duration of the hold down period. • Poison reverse - Once a connection disappears, the router advertising the connection retains the entry for several update periods, and includes an infinite cost route in its broadcasts. • To make poison reverse most effective, it must be combined with triggered updates.
- 10. RIP message format (IPv4) – RIP 2 • RIP messages can be broadly classified into two types: • routing information messages • messages used to request information.
- 11. Commands used with RIP
- 12. RIP for IPv6 (RIPng) • Called RIPng, the new protocol has an entirely new message format and even operates on a different UDP port than RIP (port 521as opposed to port520). • Like RIP2, a RIPng message does not include a size field, nor does it include a count of items that follow; a receiver computes the number of route table entries from the size of the packet (which is obtained from UDP).
- 13. Disadvantage of using Hop Counts • Using RIP or RIPng as an interior gateway protocol restricts routing to a hop-count metric. • computing routes on the basis of minimum hop counts has the severe disadvantage that it makes routing relatively static because routes cannot respond to changes in network load.
- 14. Delay Metric (HELLO) • the HELLO protocol provides an example of an IGP that was once deployed in the Internet and uses a routing metric other than hop count. • The basic idea behind HELLO is simple: use a distance-vector algorithm to propagate routing information. • HELLO uses the standard distance-vector approach for updates.
- 15. Open SPF Protocol (OSPF) • Open standard • Type of service routing • Load balancing • Hierarchical subdivision into areas • Support for authentication • Arbitrary granularity • Support for multi-access network • Multicast delivery • Virtual topology • Route importation • Direct use of IP
- 16. OSPFv2 message formats (IPv4)
- 17. OSPFv2 Hello Message Format
- 18. OSPFv2 Database Description Message Format
- 19. OSPFv2 Link-Status Request Message Format
- 20. OSPFv2 Link-Status Update Message Format
- 21. Changes In OSPFv3 To Support IPv6 • OSPFv2 used a 32-bit IP address to identify a router; OSPFv3 uses a 32-bit router ID. • OSPFv3 honors IPv6 routing scopes: link-local, area-wide, and AS- wide • The most significant change between OSPFv2 and OSPFv3 arises from the message formats. • OSPFv3 Message Formats:
- 22. OSPFv3 Hello Message Format
- 23. Other OSPFv3 Features And Messages • OSPFv3 defines several types of link-status advertisement (LSA). • For example, OSPFv3 supports router LSAs, link LSAs, interarea prefix LSAs, inter-area router LSAs, AS-external LSAs, intra-area prefix LSAs, and Not So Stubby Area(NSSA) LSAs.
- 25. Hardware Broadcast • Broadcast delivery means that the network delivers one copy of a packet to each destination. • Most hardware technologies provide a special, reserved destination address called a broadcast address. • Ethernet uses the all 1s hardware address as a broadcast address • The chief disadvantage of hardware broadcast arises from its demand on resources — in addition to using network bandwidth, each broadcast consumes computational resources on the computers attached to the network.
- 26. Hardware Multicast • The application running on a computer must ask the operating system to configure the network interface card to recognize the multicast address that has been selec • multicast addressing can be viewed as sufficiently general to include all other forms of addressing. • Although it is interesting to think of multicast addressing as a generalization that subsumes unicast and broadcast addresses, the underlying forwarding and delivery mechanisms can make multicast less efficient.
- 27. Ethernet Multicast • Ethernet provides an example of hardware multicasting, and is especially pertinent to IP multicasting. • One-half of the Ethernet address space is reserved for multicast — the low-order bit of the high order octet distinguishes conventional unicast addresses (0) from multicast addresses (1). • In dashed hexadecimal notation†, the multicast bit is given by: 01-00-00-00-00-0016
- 28. The Conceptual Building Blocks Of Internet Multicast Three conceptual building blocks are required for a general purpose internet multicasting system: • A multicast addressing scheme • An effective notification and delivery mechanism • An efficient internetwork forwarding facility
- 29. The IP Multicast Scheme General characteristics: • One IP Multicast address per group • Number of groups • Dynamic group membership • Use of hardware • Internetwork forwarding • Delivery semantics • Membership and transmission
- 30. IPv4 And IPv6 Multicast Addresses • IPv4 reserves class D addresses for multicast: the first4bits contain1110and identify the address as a multicast address. • In IPv6, a multicast address has the first8bits set to1
- 31. IPv4 Multicast Address Space • When expressed in dotted decimal notation, IPv4 multicast addresses range from 224.0.0.0 through 239.255.255.255
- 32. IPv6 Multicast Address Space
- 33. Mapping IP Multicast To Ethernet Multicast • To map an IPv4 multicast address to the corresponding Ethernet multicast address, place the low-order 23 bits of the IPv4 multicast address into the low-order 23 bits of the special Ethernet multicast address 01-00-5E-00-00-00 16 . • To map an IPv6 multicast address to the corresponding Ethernet multicast address, place the low-order 32 bits of the IPv6 multicast address into the low-order 32 bits of the special Ethernet multicast address 33-33-00-00-00-00 16.
- 34. Hosts And Multicast Delivery • multicast routers are needed to forward copies of multicast datagrams across multiple networks to all hosts participating in a multicast group. • Multicast routers listen for all IP multicast transmissions; if a multicast router is present on the network, it will receive the datagram and forward it on to another network if necessary.
- 35. Multicast Scope • The term multicast scope is used for two concepts: • to clarify the set of hosts that are listening to a given multicast group or to specify a property of a multicast address. • To clarify whether the current members of the group are on one network, multiple networks within a site, multiple networks at multiple sites within an organization, multiple networks within an administratively-defined boundary, or arbitrary networks in the global Internet. • IP uses two techniques to control multicast scope: • datagram’s hop limit field to control its range • administrative scoping
- 36. Host Participation In IP Multicasting • A host joins specific IP multicast groups on specific networks • A host can participate in IP multicast at one of three levels:
- 37. IPv4 Internet Group Management Protocol (IGMP) • When a host decides to join a multicast group, it informs a local multicast router. An IPv4 host uses the Internet Group Management Protocol (IGMP). • Although it uses IP datagrams to carry messages, we think of IGMP as an integral part of IPv4, not an independent protocol. • IGMP has two phases: Phase 1: When host joins a new multicast group Phase 2: Because membership is dynamic
- 38. IGMP Details There are several ways IGMP minimizes its effect on the network: • IGMP always uses IPv4 multicast. • Polling • A single router to poll host membership • Hosts do not respond to a router’s IGMP query simultaneously. • The host can send reports for multiple group memberships
- 39. IGMP Group Membership State Transitions
- 40. IGMP Membership Query Message Format
- 41. IGMP Membership Report Message Format
- 42. IPv6 Multicast Group Membership With MLDv2
- 43. Multicast Forwarding And Routing Information
- 44. • Unlike unicast forwarding in which routes change only when the topology changes or equipment fails, multicast routes can change simply because an application program joins or leaves a multicast group. • Unlike unicast forwarding, multicast forwarding requires a router to examine more than the destination address. • A multicast datagram may originate on a computer that is not part of the multicast group, and may be forwarded across networks that do not have any group members attached. • Reverse Path Forwarding(RPF) • When making a forwarding decision, a multicast router uses both the datagram’s source and destination addresses. The basic mechanism is known as Truncated Reverse Path Forwarding (TRPF).
- 46. Multicast Trees • forwarding tree or a delivery tree • A multicast forwarding tree is defined as a set of paths through multicast routers from a source to all members of a multicast group. • For a given multicast group, each possible source of datagrams can determine a different forwarding tree. • Unlike conventional unicast forwarding tables, each entry in a multicast table is identified by a pair: (multicast group, source)
- 47. Reverse Path Multicasting • RPM uses a two step process. • How do multicast routers learn about the location of group members? • RPM is called a broadcast and prune strategy because a router broadcasts (using RPF) until it receives information that allows it to prune a path.
- 48. Example Multicast Routing Protocols • Distance Vector Multicast Routing Protocol(DVMRP), • Core Based Trees(CBT), and • Protocol Independent Multicast(PIM).