Routing Protocols of Subject - Internetworking with TCP/IP - For B.Tech Computer Science CSVTU and BIT Durg

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

4. Unicasting
U-III
Routing
Protocols
-
Unicast
&
Multicast
Figure Unicasting
4

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

6. Multicast
Figure Multicasting
U-III
Routing
Protocols
-
Unicast
&
Multicast
6

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

41. Edge/Core Router
U-III
Routing
Protocols
-
Unicast
&
Multicast
41

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

62. Shortest Path Calculation
U-III
Routing
Protocols
-
Unicast
&
Multicast
62

63. Shortest Path Calculation
U-III
Routing
Protocols
-
Unicast
&
Multicast
63

64. Shortest Path Calculation
U-III
Routing
Protocols
-
Unicast
&
Multicast
64

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

75. IGP Vs EGP..
U-III
Routing
Protocols
-
Unicast
&
Multicast
75

76. IGP Vs EGP..
U-III
Routing
Protocols
-
Unicast
&
Multicast
76

77. IGP Vs EGP
U-III
Routing
Protocols
-
Unicast
&
Multicast
77

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

79. U-III
Routing
Protocols
-
Unicast
&
Multicast
79

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

85. U-III
Routing
Protocols
-
Unicast
&
Multicast
85

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

110. IGMP Messages
U-III
Routing
Protocols
-
Unicast
&
Multicast
110

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

114. U-III
Routing
Protocols
-
Unicast
&
Multicast
114

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

118. Multicast routing protocols
U-III
Routing
Protocols
-
Unicast
&
Multicast
118

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

120. Source based Tree
U-III
Routing
Protocols
-
Unicast
&
Multicast
120

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

122. Group-shared tree approach
U-III
Routing
Protocols
-
Unicast
&
Multicast
122

123. Multicast routing protocols
U-III
Routing
Protocols
-
Unicast
&
Multicast
123

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.

134. 134
U-III
Routing
Protocols
-
Unicast
&
Multicast

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

156. Logical tunneling
U-III
Routing
Protocols
-
Unicast
&
Multicast
156

157. MBONE
U-III
Routing
Protocols
-
Unicast
&
Multicast
157

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 ..

159. University Questions
U-III
Routing
Protocols
-
Unicast
&
Multicast
159

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