Routing Information Protocol (RIP) - PowerPoint PPT Presentation

1 / 35
About This Presentation
Title:

Routing Information Protocol (RIP)

Description:

Routing Information Protocol (RIP) NETE0514 Presented by Dr.Apichan Kanjanavapastit Intra-and Interdomain Routing An internet is divided into autonomous systems. – PowerPoint PPT presentation

Number of Views:377
Avg rating:3.0/5.0
Slides: 36
Provided by: Apic3
Category:

less

Transcript and Presenter's Notes

Title: Routing Information Protocol (RIP)


1
Routing Information Protocol (RIP)
  • NETE0514
  • Presented by
  • Dr.Apichan Kanjanavapastit

2
Intra-and Interdomain Routing
  • An internet is divided into autonomous systems.
    An autonomous system (AS) is a group of networks
    and routers under the authority of a single
    administration
  • Routing inside an autonomous system is referred
    to as intradomain routing
  • Routing between autonomous system is referred to
    as interdomain routing

3
Popular Routing Protocols
  • In this chapter, we discuss two intradomain
    routing protocols distance vector and link state
  • For the interdomain routing protocol, we
    introduce path vector
  • Routing Information Protocol (RIP) is the
    implementation of the distance vector protocol
  • Open Shortest Path First (OSPF) is the
    implementation of the link state protocol
  • Border Gateway Protocol (BGP) is the
    implementation of the path vector protocol

4
Distance Vector Routing
  • In distance vector routing, the least cost route
    between any two nodes is the route with minimum
    distance
  • In this protocol each node maintains a vector
    (table) of minimum distances to every node
  • The table at each node also guides the packets to
    the desired node by showing the next stop in the
    route (next-hop routing)

5
Initialization
  • At the beginning, each node can know only the
    distance between itself and its immediate
    neighbors, those directly connected to it

6
Sharing
  • The whole idea of distance vector routing is the
    sharing of information between neighbors
  • Although node A does not know about node E, node
    C does. So if node C shares its routing table
    with A, node A can also know how to reach node E

Note
In distance vector routing, each node shares its
routing table with its immediate neighbors
periodically and when there is a change.
7
Updating
  • When a node receives a 2-column table from a
    neighbor, it needs to update its routing table.
    Updating takes 3 steps
  • The receiving node needs to add the cost between
    itself and the sending node to each value in the
    second column
  • The receiving node needs to add the name of the
    sending node to each row as the 3rd column if the
    receiving node uses information from any row. The
    sending node is the next node in the route

8
Updating (cont.)
  • The receiving node needs to compare each row of
    its old table with the corresponding row of the
    modified version of the received table.
  • If the next-node entry is different, the
    receiving node chooses the row with the smaller
    cost. If there is a tie, the old one is kept
  • If the next-node entry is the same, the receiving
    node chooses the new row. For example, if node C
    has previously advertised a route to node X with
    distance 3. Suppose that now there is no path
    between C and X node C now advertises this route
    with a distance of infinity. Node A must not
    ignore this value even though its old entry is
    smaller.

9
Updating (cont.)
10
When to Share
  • The table is sent both periodically and when
    there is a change in the table
  • Periodic Update. A node sends its routing table,
    normally every 30 seconds, in a periodic update.
    The period depends on the protocol that is using
    distance vector routing
  • Triggered Update. A node sends its 2-column
    routing table to its neighbors any time there is
    a change in its routing table. This is called a
    triggered update. The change can result from the
    following.
  • A node receive a table from a neighbor resulting
    in changes in its own table after updating
  • A node detects some failure in the neighboring
    links which results in a distance change to
    infinity

11
Initial routing tables in a small autonomous
system
12
Final routing tables for the previous figure
13
Two-Node Loop Instability
  • A problem with distance vector routing is
    instability, which means that a network using
    this protocol can become unstable

14
Solutions to two-node instability
  • Defining Infinity. Most implementation of the
    distance vector protocol define the distance
    between each node to be 1 and define 16 as
    infinity. Therefore, the distance vector cannot
    be used in large systems
  • Split Horizon. In this strategy, instead of
    flooding the table through each interface, each
    node sends only part of its table through each
    interface. If node B thinks that the optimum
    route to reach X is via A, it does not need to
    advertise this piece of information to A.

15
Solutions to two-node instability (cont.)
16
Solutions to two-node instability (cont.)
  • Split Horizon and Poison Reverse. This strategy
    is a combination between split horizon and poison
    reverse where node B can still advertise the
    value of X, but if the source of information is
    A, it can replace the distance with infinity as a
    warning Dont use this value what I know about
    this route comes from you.

17
Solutions to two-node instability (cont.)
18
Three-Node Instability
19
Routing Information Protocol (RIP)
  • The Routing Information Protocol (RIP) is an
    intradomain routing protocol used inside an
    autonomous system
  • It is a very simple protocol based on distance
    vector routing
  • RIP implements distance vector directly with some
    considerations
  • In an autonomous, we are dealing with routers and
    networks (links). The routers have routing
    tables, networks dont
  • The destination in a routing table is a network,
    which means the first column defines a network
    address

20
Routing Information Protocol (RIP) (cont.)
  1. The metric used by RIP is the number of links
    that have to be used to reach the destination
    which is called hop count
  2. Infinity is defined as 16
  3. The next node column defines the address of the
    router to which the packet is to be sent to reach
    its destination

21
RIP Message Format
22
RIP Message Format (cont.)
  • Command. This 8-bit field specifies the type of
    message request (1) or response (2)
  • Version. This 8-bit defines the version. In the
    textbook, we use version 1
  • Family. This 16-bit field defines the family of
    the protocol used. For TCP/IP the value is 2.
  • Network address. RIP has allocated 14 bytes for
    this field to be applicable to any protocol.
  • Distance. This 32-bit field defines the hop count
    from the advertising router to the destination
    network

23
Request and Response
  • Request. A request message is sent by a router
    that has just come up or by a router that has
    some time-out entries. A request can ask about
    specific entries or all entries
  • Response. A solicited response is sent only in
    answer to a request. It contains information
    about the destination specified in the
    corresponding request. An unsolicited response is
    sent periodically, every 30 s or when there is a
    change in the routing table

24
Request Messages
25
Example 1
What is the periodic response sent by router R1?
Assume R1 knows about the whole autonomous system.
26
Solution
R1 can advertise three networks 144.2.7.0,
144.2.9.0, and 144.2.12.0. The periodic response
(update packet) is shown below.
27
Example 2
Figure 14.11 shows the update message sent from
router R1 to router R2 in Figure 14.8. The
message is sent out of interface 130.10.0.2.
See Next Slide
28
The message is prepared with the combination of
split horizon and poison reverse strategy in
mind. Router R1 has obtained information about
networks 195.2.4.0, 195.2.5.0, and 195.2.6.0 from
router R2. When R1 sends an update message to R2,
it replaces the actual value of the hop counts
for these three networks with 16 (infinity) to
prevent any confusion for R2. The figure also
shows the table extracted from the message.
Router R2 uses the source address of the IP
datagram carrying the RIP message from R1
(130.10.02) as the next hop address.
29
Timer in RIP
  • RIP uses 3 timers. The periodic timer controls
    the sending of messages, the expiration timer
    governs the validity of a route, and the garbage
    collection timer advertises the failure of a route

30
Periodic Timer
  • The periodic timer controls the advertising of
    regular update messages
  • The working model uses a random number between 25
    and 30 s
  • This is to prevent any possible synchronization
    and therefore overload on an internet if routers
    update simultaneously

31
Expiration Timer
  • The expiration timer governs the validity of a
    route
  • When a router receives update information for a
    route, the expiration timer is set to 180 s for
    that particular route
  • Every time a new update for the route is
    received, the timer is reset
  • If the timer is expired, the hop count of the
    route is set to 16, which means the destination
    is unreachable

32
Garbage Collection Timer
  • When the information about a route becomes
    invalid, the router does not immediately purge
    that route from its table
  • Instead, it continues to advertise the route with
    a metric value of 16
  • At the same time, the garbage collection timer is
    set to 120 s for that route
  • When the count reaches zero, the route is purged
    from the table

33
Example 3
A routing table has 20 entries. It does not
receive information about five routes for 200 s.
How many timers are running at this time?
SolutionThe 21 timers are listed below
Periodic timer 1 Expiration timer 20 - 5
15 Garbage collection timer 5
34
RIP Version 2
  • RIP version 2 was designed to overcome some of
    the shortcomings of version 1
  • The designers of version 2 have not augmented the
    length of the message for each entry
  • They have only replaced those fields in version 1
    that were filled with 0s for the TCP/IP protocol
    with some new fields

35
Message Format
16
8
24
31
AS NUMBER
VERSION (2)
COMMAND (1-5)
AUTHENTICATION TYPE
FFFF
AUTHENTICATION HEADER
MUST BE ZERO
FAMILY OF NET 1
ADDRESS OF NET 1
MASK
NEXT HOP
DISTANCE TO NET 1
  • Route tag. This field carries information such as
    the autonomous system number. It can be used to
    enable RIP to receive information from an
    interdomain routing protocol
  • Subnet mask. This is a 4-byte field that carries
    the subnet mask. This means that RIP2 supports
    classless addressing and CIDR
  • Next-hop address. If the sending router want to
    specify another router IP address to be the next
    hop router.
Write a Comment
User Comments (0)
About PowerShow.com