Routing Protocols
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The document discusses routing protocols in networking, focusing on unicast and multicast mechanisms, and their implementation through distance vector and link state routing algorithms. It highlights the significance of protocols like RIP and OSPF, detailing their operational characteristics, advantages, and disadvantages, as well as issues like count-to-infinity and convergence times. Furthermore, it outlines routing procedures, message formats, and the importance of secure routing practices.
![Functional Requirements(contd.)
• Routing Hierarchy
support large routing domains
• Separate internal and external routes
• Support of flexible subnetting schemes
route to arbitrary [address, mask] combinations using VLSMs (Variable
Length Subnet Mask)
• Security
• Type of Service Routing
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![Membership query message format
U-III
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Field Definition
Type = 0x11 IGMP query.
Max resp. code Maximum response code (in seconds). This field specifies the maximum time allowed before sending a responding
report.
Group address Multicast group address. This address is 0.0.0.0 for general queries.
S S flag. This flag indicates that processing by routers is being suppressed.
QRV Querier Robustness Value. This value affects timers and the number of retries.
QQIC Query Interval Code of the Querier (in seconds). This field specifies the query interval used by the querier.
No. of sources [N] Number of sources present in the query. This number is nonzero for a group-and-source query.
Source address [1...N] Address of the source(s).](https://image.slidesharecdn.com/unit-3routing-230429054921-86531a55/85/Routing-Protocols-111-320.jpg)
Routing Protocols
- 1. Routing Protocols Dr. D. P. Mishra Digitally signed by Dr. D. P. Mishra DN: cn=Dr. D. P. Mishra, o=durg, ou=BIT, email=dpmishra@bitdurg. ac.in, c=IN Date: 2023.04.29 11:18:49 +05'30'
- 2. Introduction • There are three communication mechanisms defined and classified as they related to the Internet Unicasting Multicasting Broadcasting U-III Routing Protocols - Unicast & Multicast 2
- 3. Unicast • In unicast routing, the router forwards the received packet through only one of its interfaces • In unicast routing, each router in the domain has a table that defines a shortest path tree to possible destinations U-III Routing Protocols - Unicast & Multicast 3
- 5. Multicasting • In multicasting there is one source and a group of destinations The relationship is one to many The router may forward the received packet through several of its interfaces U-III Routing Protocols - Unicast & Multicast 5
- 7. Distance Vector Routing Assumption: Each router knows only address/cost of neighbors Goal: Calculate routing table of next hop information for each destination at each router Idea: Tell neighbors about learned distances to all destinations U-III Routing Protocols - Unicast & Multicast 7
- 8. DV Algorithm • Each router maintains a vector of costs to all destinations • Initialize neighbors with known cost, others with infinity • Periodically send copy of distance vector to neighbors • On reception of a vector, if neighbors path to a destination plus neighbor cost is better, then switch to better path • Update cost in vector and next hop in routing table • Assuming no changes, will converge to shortest paths U-III Routing Protocols - Unicast & Multicast 8
- 9. DV Example – Initial Table at A D G A F E B C Dest Cost Next B 1 B C 1 C D - E 1 E F 1 F G - U-III Routing Protocols - Unicast & Multicast 9
- 10. DV Example – Final Table at A • Reached in a single iteration … simple example D G A F E B C Dest Cost Next B 1 B C 1 C D 2 C E 1 E F 1 F G 2 F U-III Routing Protocols - Unicast & Multicast 10
- 11. What if there are changes? • One scenario: Suppose link between F and G fails 1. F notices failure, sets its cost to G to infinity and tells A 2. A sets its cost to G to infinity too, since it learned it from F 3. A learns route from C with cost 2 and adopts it D G A F E B C XXXXX Dest Cost Next B 1 B C 1 C D 2 C E 1 E F 1 F G 3 C U-III Routing Protocols - Unicast & Multicast 11
- 12. • Simple example Costs in nodes are to reach Internet • Now link between B and Internet fails … Count To Infinity Problem Internet A/2 B/1 U-III Routing Protocols - Unicast & Multicast 12
- 13. Count To Infinity Problem • B hears of a route to the Internet via A with cost 2 • So B switches to the “better” (but wrong!) route update Internet A/2 B/3 XXX U-III Routing Protocols - Unicast & Multicast 13
- 14. Count To Infinity Problem • A hears from B and increases its cost update Internet A/4 B/3 XXX U-III Routing Protocols - Unicast & Multicast 14
- 15. Count To Infinity Problem • B hears from A and (surprise) increases its cost • Cycle continues and we “count to infinity” • Packets caught in the crossfire loop between A and B update Internet A/4 B/5 XXX U-III Routing Protocols - Unicast & Multicast 15
- 16. Split Horizon • Solves trivial count-to-infinity problem • Split horizon is a method of preventing a routing loop in a network. • The basic principle is simple: Information about the routing for a particular packet is never sent back in the direction from which it was received. • Split horizon can be achieved by means of a technique called poison reverse U-III Routing Protocols - Unicast & Multicast 16
- 17. Poison reverse • A poison reverse is a way in which a gateway node tells its neighbor gateways that one of the gateways is no longer connected. • To do this, the notifying gateway sets the number of hops to the unconnected gateway to a number that indicates "infinite" (meaning "You can't get there"). • Since RIP allows up to 15 hops to another gateway, setting the hop count to 16 would mean "infinite.“ • This is the equivalent of route poisoning all possible reverse paths • That is, informing all routers that the path back to the originating node for a particular packet has an infinite metric. • Split horizon with poison reverse is more effective than simple split horizon in networks with multiple routing paths U-III Routing Protocols - Unicast & Multicast 17
- 18. Routing Protocols RIP, OSPF, BGP • Dynamic protocols Sharing neighborhood information • Use different metrics. • RIP (one hop count, how many networks a packet crosses), Networks are treated equally • BGP (depend on the policy, set by administrator) • OSPF (TOS, minimize delay, maximize throughput) U-III Routing Protocols - Unicast & Multicast 18
- 19. Approaches to Shortest Path Routing There are two basic routing algorithms found on the Internet. 1. Distance Vector Routing Each node knows the distance (=cost) to its directly connected neighbors A node sends periodically a list of routing updates to its neighbors. If all nodes update their distances, the routing tables eventually converge New nodes advertise themselves to their neighbors 2. Link State Routing Each node knows the distance to its neighbors The distance information (=link state) is broadcast to all nodes in the network Each node calculates the routing tables independently U-III Routing Protocols - Unicast & Multicast 19
- 20. Routing Algorithms Distance Vector • Routing Information Protocol (RIP) • Gateway-to-Gateway Protocol (GGP) • Exterior Gateway Protocol (EGP) • Interior Gateway Routing Protocol (IGRP) Link State • Intermediate System - Intermediate System (IS-IS) • Open Shortest Path First (OSPF) • Link state routing protocols have a complete picture of the network topology. • Hence they know more about the whole network than any distance vector protocol U-III Routing Protocols - Unicast & Multicast 20
- 21. A COMPARISON: LINK STATE VS. DISTANCE VECTOR • If all routers were running a Distance Vector protocol, the path or 'route' chosen would be from A B directly over the ISDN serial link, even though that link is about 10 times slower than the indirect route from A C D B. U-III Routing Protocols - Unicast & Multicast • A Link State protocol would choose the A C D B path because it's using a faster medium (100 Mb ethernet). • In this example, it would be better to run a Link State routing protocol, but if all the links in the network are the same speed, then a Distance Vector protocol is better. 21
- 22. U-III Routing Protocols - Unicast & Multicast BASIS FOR COMPARISON DISTANCE VECTOR ROUTING LINK STATE ROUTING Algorithm Bellman ford Dijsktra Network view Topology information from the neighbour point of view Complete information on the network topology Best path calculation Based on the fewest number of hops Based on the cost Updates Full routing table Link state updates Updates frequency Periodic updates Triggered updates CPU and memory Low utilisation Intensive Simplicity High simplicity Requires a trained network administrator Convergence time Moderate Fast Updates On broadcast On multicast Hierarchical structure No Yes Intermediate Nodes No Yes A COMPARISON: LINK STATE VS. DISTANCE VECTOR 22
- 23. RIP (Routing Information Protocol) U-III Routing Protocols - Unicast & Multicast 23
- 24. RIP - Routing Information Protocol • A simple intradomain/IGP(Interiror gateway Protocol) • Open Standard , based on distance vector • Classful routing protocol (Doesn’t support subnetting) • Straightforward implementation of Distance Vector Routing • Each router advertises its distance vector every 30 seconds (or whenever its routing table changes) to all of its neighbors • RIP always uses 1 as link metric • Maximum hop count is 15, with “16” equal to “” • Routes are timeout (set to 16) after 3 minutes if they are not updated U-III Routing Protocols - Unicast & Multicast 24
- 25. RIP - History • Late 1960s : Distance Vector protocols were used in the ARPANET • Mid-1970s: XNS (Xerox Network system) routing protocol is the precursor of RIP in IP (and Novell’s IPX RIP and Apple’s routing protocol) • 1982 Release of routed for BSD Unix • 1988 RIPv1 (RFC 1058) - classful routing • 1993 RIPv2 (RFC 1388) - adds subnet masks with each route entry - allows classless routing • 1998 Current version of RIPv2 (RFC 2453) U-III Routing Protocols - Unicast & Multicast 25
- 26. RIPv1 • RIP Characteristics -A classful, Distance Vector (DV) routing protocol -Metric = hop count -Routes with a hop count > 15 are unreachable -Updates are broadcast every 30 seconds U-III Routing Protocols - Unicast & Multicast 26
- 27. RIPv1 Packet Format IP header UDP header RIP Message Command Version Set to 00...0 32-bit address Unused (Set to 00...0) address family Set to 00.00 Unused (Set to 00...0) metric (1-16) one route entry (20 bytes) Up to 24 more routes (each 20 bytes) 32 bits One RIP message can have up to 25 route entries 1: request 2: response 2: for IP 0…0: request full rou- ting table Address of destination Cost (measured in hops) 1: RIPv1 U-III Routing Protocols - Unicast & Multicast 27
- 28. RIPv2 • RIPv2 is an extends RIPv1: Subnet masks are carried in the route information Authentication of routing messages Route information carries next-hop address Exploites IP multicasting • Extensions of RIPv2 are carried in unused fields of RIPv1 messages U-III Routing Protocols - Unicast & Multicast 28
- 29. RIPv2 Packet Format IP header UDP header RIP Message Command Version Set to 00...0 32-bit address Unused (Set to 00...0) address family Set to 00.00 Unused (Set to 00...0) metric (1-16) one route entry (20 bytes) Up to 24 more routes (each 20 bytes) 32 bits One RIP message can have up to 25 route entries 1: request 2: response 2: for IP 0…0: request full rou- ting table Address of destination Cost (measured in hops) 2: RIP v U-III Routing Protocols - Unicast & Multicast 29
- 30. RIPv2 Packet Format IP header UDP header RIPv2 Message Command Version Set to 00.00 IP address Subnet Mask address family route tag Next-Hop IP address metric (1-16) one route entry (20 bytes) Up to 24 more routes (each 20 bytes) 32 bits Used to carry information from other routing protocols (e.g., autonomous system number) Identifies a better next-hop address on the same subnet than the advertising router, if one exists (otherwise 0….0) 2: RIPv2 Subnet mask for IP address U-III Routing Protocols - Unicast & Multicast 30
- 31. RIP Messages • This is the operation of RIP in routed. • Dedicated port for RIP is UDP port 520. • Two types of messages: Request messages used to ask neighboring nodes for an update Response messages contains an update U-III Routing Protocols - Unicast & Multicast 31
- 32. Routing with RIP • Initialization: Send a request packet (command = 1, address family=0..0) on all interfaces: RIPv1 uses broadcast if possible, RIPv2 uses multicast address 224.0.0.9, if possible requesting routing tables from neighboring routers • Request received: Routers that receive above request send their entire routing table • Response received: Update the routing table • Typically, there is a routing daemon (routed) that is an application layer process that provides access to routing tables. U-III Routing Protocols - Unicast & Multicast 32
- 33. Routing with Rip Cont. • Regular routing updates: Every 30 seconds, send all or part of the routing tables to every neighbor in an response message • Triggered Updates: Whenever the metric for a route change, send entire routing table. • If a router does not hear from its neighbor once every 180 seconds, the neighbor is deemed unreachable. U-III Routing Protocols - Unicast & Multicast 33
- 34. RIP Convergence • Takes more time to converge • RIP requires less CPU power and RAM than other routing protocols • Router advertises details to its neighbors • Routing by rumors, similar to rumor spread by peoples living in locality/neighbors U-III Routing Protocols - Unicast & Multicast 34
- 35. Security • Issue: Sending bogus routing updates to a router • RIPv1: No protection • RIPv2: Simple authentication scheme U-III Routing Protocols - Unicast & Multicast 35
- 36. RIP Security IP header UDP header RIPv2 Message Command Version Set to 00.00 Password (Bytes 0 - 3) Password (Bytes 4 - 7) 0xffff Authentication Type Password (Bytes 8- 11) Password (Bytes 12 - 15) Authetication Up to 24 more routes (each 20 bytes) 32 bits 2: plaintext password U-III Routing Protocols - Unicast & Multicast 36
- 37. RIP Advantages • Easy to configure • No Design constraint • No Complexity • Less overhead U-III Routing Protocols - Unicast & Multicast 37
- 38. RIP Disadvantages • RIP takes a long time to stabilize / slow convergence • Work only on hop count • Bandwidth utilization is high as routing table entry is heard after every 30 Sec • RIP has all the problems of distance vector algorithms, e.g., count-to- Infinity RIP uses split horizon to avoid count-to-infinity • Not scalable as • The maximum path in RIP is 15 hops U-III Routing Protocols - Unicast & Multicast 38
- 39. Edge Router • An edge router is a specialized router located at a network boundary that enables a campus network to connect to external networks U-III Routing Protocols - Unicast & Multicast 39
- 40. Core Router • A core router is a computer communication system device and a network’s backbone, • i.e. the device linking all network devices. • It provides multiple fast data communication interfaces. • The word "core" refers to a network’s overall physical structure. U-III Routing Protocols - Unicast & Multicast 40
- 42. OSPF(Open Shortest Path First) 1 U-III Routing Protocols - Unicast & Multicast 42
- 43. Introduction • Development began in 1987 • OSPF Working Group (part of IETF) • OSPFv2 first established in 1991 • Many new features added since then • Updated OSPFv2 specification in RFC 2178 U-III Routing Protocols - Unicast & Multicast 43
- 44. Motivation • Original IGP used was RIP • Based on Bellman-Ford Algorithm • Worked well in small systems • Suffered from problems of Distance Vector Protocol Count to Infinity Problem Slow Convergence U-III Routing Protocols - Unicast & Multicast 44
- 45. Functional Requirements of OSPF • Faster Convergence and less consumption of network resources • A more descriptive routing metric configurable value ranges between 1 and 65,535 no restriction on network diameters • Equal-cost multipath a way to do load balancing U-III Routing Protocols - Unicast & Multicast 45
- 46. Functional Requirements(contd.) • Routing Hierarchy support large routing domains • Separate internal and external routes • Support of flexible subnetting schemes route to arbitrary [address, mask] combinations using VLSMs (Variable Length Subnet Mask) • Security • Type of Service Routing U-III Routing Protocols - Unicast & Multicast 46
- 47. OSPF Operation •Every OSPF router sends out 'hello' packets • Hello packets used to determine if neighbor is up • Hello packets are small easy to process packets • Hello packets are sent periodically (usually short interval) U-III Routing Protocols - Unicast & Multicast 47
- 48. The Hello Packet • Router priority • Hello interval • Router dead interval • Network mask • List of neighbors FDDI Dual Ring Hello Hello Hello 10 U-III Routing Protocols - Unicast & Multicast 48
- 49. Link State Advertisements(LSAs) LS Age Options LS Type Link State ID Advertising Router LS Sequence Number LS Checksum Length LSA Header 0 16 U-III Routing Protocols - Unicast & Multicast 49
- 50. LSAs contd. • Identifying LSAs LS type field Link State ID field mostly carries addressing information e.g. IP address of externally reachable network Advertising Router field originating router’s OSPF router ID U-III Routing Protocols - Unicast & Multicast 50
- 51. LSAs contd. • Identifying LSA instances needed to update self-originated LSAs LS Sequence Number field 32 bit values monotonically increasing until some max value 600 years to roll over! LSA checksum and LS Age guard against potential problems U-III Routing Protocols - Unicast & Multicast 51
- 52. LSAs contd. • Verifying LSA contents LS Checksum field computed by the originating router and left unchanged thereafter LS age field not included in checksum • Removing LSAs from databases LS Age field ranges from 0 to 30 min. Max Age LSAs used to delete outdated LSAs U-III Routing Protocols - Unicast & Multicast 52
- 53. LSAs contd. • Other LSA Header fields Options field sometimes used to give special treatment during flooding or routing calculations Length field includes LSA header and contents ranges from 20-65535 bytes U-III Routing Protocols - Unicast & Multicast 53
- 54. Open Shortest Path First (RFC 1247) • Uses IP, has a value in the IP Header (8 bit protocol field) • Interior routing protocol, its domain is also an autonomous system • Special routers (autonomous system boundary routers) or backbone routers responsible to dissipate information about other AS into the current system. • Divides an AS into areas • Metric based on type of service Minimum delay (rtt), maximum throughput, reliability, etc.. U-III Routing Protocols - Unicast & Multicast 54
- 55. OSPF (type of links) U-III Routing Protocols - Unicast & Multicast 55
- 56. Point-to-point Link U-III Routing Protocols - Unicast & Multicast Point –to – point link defines direct connection between routers and it can be represented as graph with link having bidirectional arrow 56
- 57. Transient Link U-III Routing Protocols - Unicast & Multicast This link defines network to which multiple routers are attached, in this type of network multiple routers are connected to common network and they have many neighbors 57
- 58. Stub Links U-III Routing Protocols - Unicast & Multicast This link is special case of transient link, which defines a network with only one router connected to it, packet enters and leave the network using single link 58
- 59. Virtual Links U-III Routing Protocols - Unicast & Multicast When the link between two routers is broken, a new link has to be established by the administrator, which is known as virtual link 59
- 60. OSPF (link state advertisement) Router Link Network Link U-III Routing Protocols - Unicast & Multicast 60
- 61. OSPF (LSA cont.) Summary link to Network Summary link to AS boundary router External Link U-III Routing Protocols - Unicast & Multicast 61
- 65. Types of OSPF packets and header format U-III Routing Protocols - Unicast & Multicast 65
- 66. Link State Update Packet A router link example LSA header not covered Refer to RFC 1247 U-III Routing Protocols - Unicast & Multicast 66
- 67. A Network Link Example U-III Routing Protocols - Unicast & Multicast 67
- 68. Summary Links state Advertisements Summary link to network Summary link to AS boundary External Link U-III Routing Protocols - Unicast & Multicast 68
- 69. Advantages of OSPF: • Biggest advantage of OSPF over EIGRP is that it will run on any device as its based on open standard • OSPF is an open standard, not related to any particular vendor. • It uses the SPF algorithm, developed by Dijkstra, to provide a loop- free topology. • OSPF is hierarchical, using area 0 as the top as the hierarchy. OSPF is a Link State Algorithm. • It provides fast convergence with triggered, incremental updates via Link State Advertisements (LSAs). • It is a classless protocol and allows for a hierarchical design with VLSM and route summarization. U-III Routing Protocols - Unicast & Multicast 69
- 70. Disadvantages of OSPF • It requires extra CPU processing to run the SPF algorithm • It is complex to configure and more difficult to troubleshoot. • OSPF maintains multiple copies of routing information, increasing the amount of memory needed, i.e. it requires more memory to hold the adjacency (list of OSPF neighbors), topology and routing tables. • In the case where an entire network is running OSPF, and one link within it is "bouncing" every few seconds • OSPF routers check the status of other routers on the network by sending a small hello packet at regular intervals. • If a router does not respond to the hello packet, it is assumed dead, and routing updates are sent to every other router by using a multicast address. U-III Routing Protocols - Unicast & Multicast 70
- 71. Summary • Why OSPF is needed in the Internet? • The basics of the protocol The Link state Advertisements Neighbor Discovery (Hello Protocol) Database Synchronization and reliable flooding • Hierarchical Routing in OSPF OSPF Areas and Area Organization Interaction with External Routing Information U-III Routing Protocols - Unicast & Multicast 71
- 72. BGP (Border Gateway Protocol) U-III Routing Protocols - Unicast & Multicast 72
- 73. Basic Terms • IGP(Interior Gateway Protocol) -RIP, IGRP, EIGRP, OSPF = Routing protocol used to exchange routing information within an autonomous system. • EGP(Exterior Gateway Protocol) -BGP = Routing protocol used to exchange routing information between autonomous systems. • Autonomous System= (From RFC 1771) “A set of routers under the single technical administration, using an IGP and common metrics to route packets within the AS, and using an EGP to route packets to other AS’s.” • BGP is a path vector or an advanced distance vector routing protocol. U-III Routing Protocols - Unicast & Multicast 73
- 74. IGP Vs EGP. • Interior gateway protocol (IGP) • A routing protocol operating within an Autonomous System (AS). • RIP, OSPF, and EIGRP are IGPs. • Exterior gateway protocol (EGP) • A routing protocol operating between different AS. • BGP is an interdomain routing protocol (IDRP) and is an EGP. U-III Routing Protocols - Unicast & Multicast 74
- 78. Based on Path Vector Routing • Example of unicast routing protocol , and it is useful for interdomain routing • Assumes that there is one node in each autonomous system that acts on behalf of the entire autonomous system is called Speaker node • The speaker node in an AS creates a routing table and advertises to the speaker node in the neighboring ASs • A speaker node advertises the path, not the metrics of the nodes, in its autonomous system or other autonomous systems U-III Routing Protocols - Unicast & Multicast 78
- 80. Border Gateway Protocol (RFC 1771) • Based on the path vector routing. • Distance-vector protocol not preferred for inter-AS routing (exterior routing protocol) Assumes all routers have a common distance metrics to judge route preferences. If routers have different meanings of a metric, it may not be possible to create stable, loop free routes. A given AS may have different priorities from another AS. Gives no information about the ASs that will be visited. • Link-state routing protocol Different metrics. Flooding is not realistic. • Differs from DVA Path vector approach does not include a distance or cost estimate Lists all of the ASs visited to reach destination network. • Path vector routing No metrics, Information about which networks can be reached by a given router and ASs to be crossed. U-III Routing Protocols - Unicast & Multicast 80
- 81. BGP • Border Gateway Protocol (BGP) used to route traffic across the Internet. • For that reason, it's a pretty important protocol • One should realize that routing in the Internet is comprised of two parts: The internal fine-grained portions managed by an IGP such as OSPF, Interconnections of autonomous systems (AS) by EGP such as BGP. U-III Routing Protocols - Unicast & Multicast 81
- 82. Who needs to understand BGP? • BGP is relevant to network administrators of large organizations which connect to two or more ISPs, • Internet Service Providers (ISPs) who connect to other network providers. • Administrator of a small corporate network, or an end user, - need not to know about BGP. U-III Routing Protocols - Unicast & Multicast 82
- 83. BGP Basics • The current version of BGP is BGP version 4, based on RFC4271. • BGP is the path-vector protocol that provides routing information for autonomous systems on the Internet via its AS-Path attribute. • BGP is a Layer 4 protocol that sits on top of TCP. • It is much simpler than OSPF, because it doesn’t have to worry about the things TCP will handle. • There is no discovery in BGP. • An important aspect of BGP is that the AS-Path itself is an anti-loop mechanism. • Routers will not import any routes that contain themselves in the AS- Path. U-III Routing Protocols - Unicast & Multicast 83
- 84. Path Vector Routing • A path vector protocol does not rely on the cost of reaching a given destination to determine whether each path available is loop free or not. • Instead, path vector protocols rely on analysis of the path to reach the destination to learn if it is loop free or not. • A path vector protocol guarantees loop free paths through the network by recording each hop the routing advertisement traverses through the network. • In this case, router A advertises reachability to the 10.1.1.0/24 network to router B. When router B receives this information, it adds itself to the path, and advertises it to router C. Router C adds itself to the path, and advertises to router D that the 10.1.1.0/24 network is reachable in this direction. U-III Routing Protocols - Unicast & Multicast 84
- 86. BGP (continued) • Messages are sent over TCP connections on port 179. • Functional procedures Neighbor acquisition (open message, acceptance through Keepalive message) Neighbor reachability (periodic Keepalive messages) Network reachability (broadcast an update message) Each routers maintains a database of networks that can be reached + preferred route to this network. • RFC does not address How a router knows the address of another router. Up to network admin. U-III Routing Protocols - Unicast & Multicast 86
- 87. OPEN Message Routers use this message to identify itself and to specify its BGP operational parameters. Open message is always send when the TCP session is established between neighbors. • Version – specifies the version (2,3 or 4), default 4. • Autonomous System – provides AS number of the sender. It determines whether the BGP session is EBGP or IBPG (if the AS number are the same ) • Hold-Time – indicates the maximum number of seconds that can elapse without receipt of message before transmitter is assumed to be nonfunctional ( CISCO 180 Sec) • BGP Identifier – Provides the BGP identifier of the sender (an IP address). U-III Routing Protocols - Unicast & Multicast 87
- 88. UPDATE MESSAGE • Advertises feasible routes, withdrawn routes or both. Update message contains five fields : • Unfeasible Routes Length – Indicates the total length of the withdrawn routes field or that the field is not present. • Withdrawn Routes — Contains a list of IP address prefixes for routes being withdrawn from. • Total Path Attribute Length — Indicates the total length of the path attributes field or that the field is not present. • Path Attributes — Describes the characteristics of the advertised path. The following are possible attributes for a path • Network Layer Reachability Information (NLRI) — Contains a list of IP address prefixes for the advertised routes. U-III Routing Protocols - Unicast & Multicast 88
- 89. KEEPALIVE • If a router accepts the parameters specified in Open message, it responds Keepalive. • By default Cisco sends keep-alive every 60 sec or a period equal to 1/3 the hold time. U-III Routing Protocols - Unicast & Multicast 89
- 90. Notification • This message is sent whenever something bad has happened, e.g. an error is detected and causes the BGP connection to close. • Error Code — Indicates the type of error that occurred. The following are the error types defined by the field: • Error Subcode — Provides more specific information about the nature of the reported error. • Error Data — Contains data based on the error code and error subcode fields. This field is used to diagnose the reason for the notification message. U-III Routing Protocols - Unicast & Multicast 90
- 91. BGP (cont.) • Loop Prevention in BGP: Checks the Path before updating its database. (If its AS is in the path ignore the message) • Policy Routing: If a path consist of an AS against the policy of the current AS, message discarded. Network Next router Path N1 R1 AS14,AS23,AS67 N2 R5 AS22,AS67,AS5,AS89 N3 R6 AS67,AS89,AS9,AS34 N4 R12 AS62,AS2,AS9 Example of Network Reachability Example of Message adverstisements U-III Routing Protocols - Unicast & Multicast 91
- 92. BGP message format (Open, Keepalive, Update, Notification U-III Routing Protocols - Unicast & Multicast 92
- 93. BGP message format (Open, Keepalive, Update, Notification U-III Routing Protocols - Unicast & Multicast 93
- 94. BGP message format (Open, Keepalive, Update, Notification U-III Routing Protocols - Unicast & Multicast 94
- 95. BGP message format (Open, Keepalive, Update, Notification U-III Routing Protocols - Unicast & Multicast 95
- 96. When to use BGP • Use BGP when the effects of BGP are well understood and one of the following conditions exist: • The AS allows packets to transit through it to reach another AS (transit AS). • The AS has multiple connections to other AS’s. • The flow of traffic entering or exiting the AS must be manipulated. This is policy based routing and based on attributes. U-III Routing Protocols - Unicast & Multicast 96
- 97. When not to use BGP Do not use BGP if you have one or more of the following conditions: • A single connection to the Internet or another AS • No concern for routing policy or routing selection • A lack of memory or processing power on your routers to handle constant BGP updates • A limited understanding of route filtering and BGP path selection process • Low bandwidth between AS’s U-III Routing Protocols - Unicast & Multicast 97
- 98. Advantages of BGP • BGP is more scalable than OSPF. • BGP handle such large routes between AS. • BGP handle ISP level of routing with large number of routes whereas ospf cannot handle. • BGP allows more options for routing manipulations and optimization by using routing policies U-III Routing Protocols - Unicast & Multicast 98
- 99. Disadvantages of BGP • BGP is not used on a internal corporate network. • IGP protocols, (OSPF or ISIS(Intermediate System- Intermediate System)) are usually more suited for that. • BGP is more often used when you are interconnecting backbones or using more advanced protocols like MPLS. U-III Routing Protocols - Unicast & Multicast 99
- 100. Multicasting / Multicast Routing U-III Routing Protocols - Unicast & Multicast 100
- 101. What is multicast routing? • Multicast routing protocols are used to distribute data (for example, audio/video streaming broadcasts) to multiple recipients. • Can send a single copy of data to a single multicast address, which is then distributed to an entire group of recipients. • Routers between the source and recipients duplicate data packets and forward multiple copies wherever the path to recipients diverges. • Group membership information is used to calculate the best routers at which to duplicate the packets in the data stream. • A source host sends data to a multicast group by simply setting the destination IP address of the datagram for multicast group. • Any host can become a source and send data to a multicast group. U-III Routing Protocols - Unicast & Multicast 101
- 102. What is multicast routing? • There are several multicast protocols & mode, they operate in same general way, as follows. • A Multicast Group Membership Discovery protocol is used by receiving hosts to advertise their group membership to a local multicast router, enabling them to join and leave multicast groups. • The main Multicast Group Membership Discovery protocols are Internet Group Management Protocol (IGMP) for IPv4 Multicast Listener Discovery (MLD) for IPv6. • A Multicast Routing Protocol is used to communicate between multicast routers & enables them to calculate multicast tree • Protocol Independent Multicast (PIM) is the most important Multicast Routing Protocol. • The multicast distribution tree nodes holds the route to every recipient that has joined the multicast group, and its optimized in such a way that multicast traffic reaches to intended nodes only • Duplicate copies of packets are kept to a minimum. U-III Routing Protocols - Unicast & Multicast 102
- 103. In unicast routing, each router in the domain has a table that defines a shortest path tree to possible destinations. U-III Routing Protocols - Unicast & Multicast 103
- 104. 104 In unicast routing, the router forwards the received packet through only one of its interfaces. Unicasting U-III Routing Protocols - Unicast & Multicast
- 105. In multicast routing, each involved router needs to construct a shortest path tree for each group. U-III Routing Protocols - Unicast & Multicast 105
- 106. 106 Multicasting In multicast routing, the router may forward the received packet through several of its interfaces. U-III Routing Protocols - Unicast & Multicast
- 107. 107 Application of Multicasting • Access to Distributed Databases • Information Dissemination: e.g. multicast software updates to customers • News Delivery, Stock quotes, sports scores, magazines, newspaper • Teleconferencing, Web Seminars, Distant Learning • Advertisements • Seminars, conferences, workshops .... U-III Routing Protocols - Unicast & Multicast
- 108. • Multicast means that a sender sends a message to a group of recipients who are members of the same group. • Each multicast router needs to know the list of groups that have at least one loyal member related to each interface. • Collection of this type of information is done at two levels: locally and globally. • The first task is done by the IGMP protocol; the second task is done by the multicast routing protocols. Role of IGMP in Multicasting U-III Routing Protocols - Unicast & Multicast 108
- 109. Position of IGMP U-III Routing Protocols - Unicast & Multicast IGMP is a group management protocol. It helps a multicast router to create and update a list of loyal members related to each router interface. 109
- 111. Membership query message format U-III Routing Protocols - Unicast & Multicast 111 Field Definition Type = 0x11 IGMP query. Max resp. code Maximum response code (in seconds). This field specifies the maximum time allowed before sending a responding report. Group address Multicast group address. This address is 0.0.0.0 for general queries. S S flag. This flag indicates that processing by routers is being suppressed. QRV Querier Robustness Value. This value affects timers and the number of retries. QQIC Query Interval Code of the Querier (in seconds). This field specifies the query interval used by the querier. No. of sources [N] Number of sources present in the query. This number is nonzero for a group-and-source query. Source address [1...N] Address of the source(s).
- 112. Three forms of query messages U-III Routing Protocols - Unicast & Multicast 112 In case of General - A router sets following fields in the IGMP header: Type is set to 0x11. Max-response-code is calculated based on the configured value of 'maximum-response- time'. 'checksum' is calculated by initializing the checksum field with 0
- 113. Membership Report Message Format U-III Routing Protocols - Unicast & Multicast 113
- 115. 115 Multicast Routing objectives Objectives • Every member receives EXACTLY ONE copy of the packet • Non-members receive nothing • No loops in route • Optimal path from source to each destination. Terminology • Spanning Tree: Source is the root, group members are the leaves. • Shortest Path Spanning Tree: Each path from root to a leaf is the shortest according to some metric U-III Routing Protocols - Unicast & Multicast
- 116. Brief History . • In 1995 the first mcast network came in existence: MBone • DVMRP (Distance Vector Multicast Routing Protocol) was the protocol used DVMRP subnetworks was interconnected through the unicast Internet infrastructure with tunnels Flood and Prune technology Very successful in academic circles U-III Routing Protocols - Unicast & Multicast 116
- 117. Problem with DVMRP DVMRP can’t scale to Internet sizes Distance vector-based routing protocol Periodic updates Full table refresh every 60 seconds Table sizes Internet > 40,000 prefixes at that moment Scalability Too many tunnels, hop-count till 32 hops, etc => In 1997, a native protocol is developed, Protocol Independent Multicast Brief History .. U-III Routing Protocols - Unicast & Multicast 117
- 119. 119 Multicast Trees • Source-Based Tree: For each combination of (source , group), there is a shortest path spanning tree. Approach 1: DVMRP; an extension of unicast distance vector routing (e.g. RIP) Approach 2: MOSPF; an extension of unicast link state routing (e.g. OSPF) Best for one-to-many distribution • Group-Share Tree One tree for the entire group Best for Many-to-Many distribution Rendezvous-Point Tree: one router is the center of the group and therefore the root of the tree. CBT and PIM-SP protocols. U-III Routing Protocols - Unicast & Multicast
- 121. Group-Shared Tree • In the group-shared tree approach, only the core router, which has a shortest path tree for each group, is involved in multicasting • If a router receives a multicast packet, it encapsulates the packet in a unicast packet and sends it to the core router • The core router removes the multicast packet from its capsule, and consults its routing table to route the packet U-III Routing Protocols - Unicast & Multicast 121
- 124. 124 Distance Vector Multicast Routing Protocol - DVMRP • No pre-defined route from source to destination. • Tree is gradually created by successive routers along the path. • Uses shortest path (fewest hops) • Prevent loops: apply Reverse Path Forwarding (RPF) • Prevent Duplication: apply Reverse Path Broadcasting (RPB) • Multicast with dynamic membership: apply Reverse Path Multicasting (RPM) with pruning, grafting, and lifetime. U-III Routing Protocols - Unicast & Multicast
- 125. 125 Reverse Path Forwarding In reverse path forwarding (RPF), the router forwards only packets that have traveled the shortest path from the source to the router; all other copies are discarded. No Loops U-III Routing Protocols - Unicast & Multicast
- 126. 126 Reverse Path Broadcasting Prevent Duplication in RPF U-III Routing Protocols - Unicast & Multicast
- 127. 127 RPB creates a shortest path broadcast tree from the source to each destination It guarantees that each destination receives one and only one copy of the packet. U-III Routing Protocols - Unicast & Multicast
- 128. 128 RPF, RPB, and RPM RPM adds pruning and grafting to RPB to create a multicast shortest path tree that supports dynamic membership changes. U-III Routing Protocols - Unicast & Multicast
- 129. Multicast link state routing uses the source-based tree approach. U-III Routing Protocols - Unicast & Multicast 129
- 130. 130 MOSPF (1) • Group membership LSA is flooded throughout the AS • The router calculates the shortest path trees on demand (when it receives the first multicast packet) • MOSPF is a data-driven protocol; the first time an MOSPF router see a datagram with a given source and group address, the router constructs the Dijkstra shortest path tree U-III Routing Protocols - Unicast & Multicast
- 131. U-III Routing Protocols - Unicast & Multicast 131 MOSPF (2) • The shortest path tree is made all at once instead of gradually (i.e. pre-made, pre- pruned, ready to use)
- 132. U-III Routing Protocols - Unicast & Multicast 132 MOSPF with Areas (1) • Group management Group-membership LSA is flooded in the same area. Inter-area multicast forwarders (area border routers) summarize their attached areas' group membership to the backbone. • Data routing Introduction of the wild-card multicast receivers (area border routers)
- 133. U-III Routing Protocols - Unicast & Multicast 133 MOSPF with Areas (2) • Data routing (cont) 1. Source area: building intra-area shortest path tree (forward cost) with leaf nodes including wild- card multicast receivers. 2. Backbone area: each wild-card multicast receiver of the source area calculates the shortest path from the source to the multicast forwarders (with group members) of other areas using the reverse cost.
- 135. U-III Routing Protocols - Unicast & Multicast 135 Multicast Distance Vector Routing 4 decision-making strategies 1. Flooding 2. Reverse Path Forwarding (RPF) 3. Reverse Path Broadcasting (RPB) 4. Reverse Path Multicasting (RPM)
- 136. Flooding broadcasts packets, but creates loops in the systems. U-III Routing Protocols - Unicast & Multicast 136
- 137. RPF eliminates the loop in the flooding process. U-III Routing Protocols - Unicast & Multicast 137
- 138. RPB creates a shortest path broadcast tree from the source to each destination. It guarantees that each destination receives one and only one copy of the packet. U-III Routing Protocols - Unicast & Multicast 138
- 139. RPM adds pruning and grafting to RPB to create a multicast shortest path tree that supports dynamic membership changes. U-III Routing Protocols - Unicast & Multicast 139
- 140. CBT( Core Based Tree) U-III Routing Protocols - Unicast & Multicast 140
- 141. CBT • Latest addition to existing set of multicast forwarding algorithm • Unlike existing algorithms which build source based tree on pair (S, G) CBT constructs a single delivery tree that is shared by all the group members • CBT is similar to spanning algorithm, except it allows to create different CBT for each group • Multicast traffic for each group is send on received over the same delivery tree regardless of source U-III Routing Protocols - Unicast & Multicast 141
- 142. U-III Routing Protocols - Unicast & Multicast 142 Formation of CBT tree (1) • After the rendezvous point is selected, every router is informed of the unicast address of the selected router • Each router sends a unicast join message to show that it wants to join the group • This message passes through all routers that are located between the sender and the rendezvous router
- 143. U-III Routing Protocols - Unicast & Multicast 143 • Each intermediate router extracts the necessary information from the message Unicast address of the sender Interface through which the packet has arrived • Every router knows its upstream router and the downstream router • If a router wants to leave the group, it sends a leave message to its upstream router, … Formation of CBT tree (2)
- 144. Group-shared tree with rendezvous router
- 145. Sending a multicast packet to the rendezvous router U-III Routing Protocols - Unicast & Multicast 145
- 146. In CBT, the source sends the multicast packet (encapsulated in a unicast packet) to the core router. The core router decapsulates the packet and forwards it to all interested interfaces. U-III Routing Protocols - Unicast & Multicast 146
- 147. CBT Advantages • Less traffic • Less periodic refresh • CBT makes efficient use of router resources – since it requires router to maintain state information of each group not for each (Source, Group) pair • CBT conserves Network bandwidth – since doesn’t require that all multicast frames to be periodically forwarded to all the multicast routers U-III Routing Protocols - Unicast & Multicast 147
- 148. CBT Limitations • May result traffic concentration and bottleneck near core router • Single shared tree may create suboptimal route that may result increased delay • The Core as a Single Point of Failure • Core Placement : Core based trees may not provide the most optimal paths between members of a group. • Proposed not really used anywhere U-III Routing Protocols - Unicast & Multicast 148
- 149. 149 Comparisons • The tree for DVMRP and MOSPF is made from the root up • The tree for CBT is formed from the leaves down • In DVMRP, the tree is first made (broadcasting) and then pruned • In CBT, the joining gradually makes the tree, and the source in CBT may or may not be part of the tree U-III Routing Protocols - Unicast & Multicast
- 150. PIM-DM is used in a dense multicast environment, such as a LAN. U-III Routing Protocols - Unicast & Multicast 150
- 151. U-III Routing Protocols - Unicast & Multicast 151 PIM-DM • It is used when there is a possibility that each router is involved in multicasting (dense mode) • In this environment, the use of a protocol that broadcasts the packet is justified because almost all routers are involved in the process
- 152. PIM-DM uses RPF and pruning/grafting strategies to handle multicasting. However, it is independent from the underlying unicast protocol. U-III Routing Protocols - Unicast & Multicast 152
- 153. PIM-SM is used in a sparse multicast environment such as a WAN. U-III Routing Protocols - Unicast & Multicast 153
- 154. PIM-SM is similar to CBT but uses a simpler procedure. U-III Routing Protocols - Unicast & Multicast 154
- 155. • Increase in Multimedia and real-time communication need for multicasting in the Internet. • Small fraction of Internet routers are multicast routers. • Problem may be solved by adding more no. of multicast routers in coming years meanwhile solution at present is Tunneling. • The multicast routers are seen as a group of routers on top of unicast routers. • The multicast routers may not be connected directly, but they are connected logically. MBONE MBONE U-III Routing Protocols - Unicast & Multicast 155
- 158. Issues of MBONE U-III Routing Protocols - Unicast & Multicast 158 The routing protocols for MBONE are still immature and their ongoing design is a central part of this network experiment. Most MBONE routers employ the Distance Vector Multicast Routing Protocol(DVMRP) which is commonly considered inadequate for rapidly changing network topologies because routing information ..
- 160. U-III Routing Protocols - Unicast & Multicast 160 APRIL- MAY 2019 (Compulsory For all) 1(a) Explain the following terms related with routing (i) Interior Routing (ii)Exterior Routing 2M (b) Draw the frame format of following BGP Message and explain the different fields (i) Open message (ii)Update message (iii)Keep-alive message 7M (c) How does MOSPF use Dijkstras’ algorithm ? 7M (d) Explain the principle of DVMRP also explain the use of cached information in DVMRP to minimize the multicast tree 7M
- 161. U-III Routing Protocols - Unicast & Multicast 161 APRIL- MAY 2018 (Compulsory For all) 1(a) “Routers are having their own flash to build routing table“, Justify the given statement 2M (b) (i) User 1 types www.csvtu.ac.in on the browser window. What would be the destination port number, When the DNS Request is sent to DNS server by user 1 (ii) User 2 pings www.csvtu.ac.in. Is the DNS server required for ping to be successful? (iii) What has to be established before HTTP data can be sent or received from user1 to webserver ? (iv) User1 and user2 simultaneously type www.csvtu.ac.in on the browser of repective computers . How does the server differentiate between the connection (v) Will the communication be disrupted between the webserver and users if the DNS server goes down during data transfer between webserver and the users ? 7M (c) Explain RIP in detail by specifying the working of Distance Vector routing and RIP Updation algorithm 7M (d) Draw the frame format of following BGP messages and Explain the different fields (i) Open message , (ii) Update message (iii) Keep-alive message (iv) Notification message 7M
- 162. U-III Routing Protocols - Unicast & Multicast 162 APRIL- MAY 2017 1(a) Define Autonomous system 2M (b) Compare RIP With OSPF 7M (c) What do you mean by source based tree multicasting protocol ? Write a technical note on MOSPF 7M (d) What do you mean by logical tunnel ? Write a technical note on MBONE 7M
- 163. U-III Routing Protocols - Unicast & Multicast 163 APRIL- MAY 2016 1(a) In multicasting there is a : (i) One source and one destination (ii) One source and group of destinations (iii) One source and all hosts on the network (iv) None of the above 2M (b) Explain different types of packets used by OSPF routing protocol 7M (c) Briefly explain MBONE 7M (d) Explain Distance vector routing with example 7M
- 164. U-III Routing Protocols - Unicast & Multicast 164 APRIL- MAY 2015 1(a) In multicast address for a group is 232.43.14.7 what is its 48-bit Ethernet address for LAN using TCP/IP 2M (b) Explain the working of OSPF using different types of OSPF Packets 7M (c) Explain the working of CBT with Example 7M (d) Explain the working of BGP 7M