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Routing Fundamentals and Subnets

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The frame header and trailer are removed and the packet is passed up to Layer 3. ... Packets NEVER travel through the network they are carried within frames ... – PowerPoint PPT presentation

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Title: Routing Fundamentals and Subnets


1
Routing Fundamentals and Subnets
  • Objectives
  • Routed Protocols
  • IP Routing Protocols
  • The Mechanism of Subnetting
  • By
  • Adwoa Afful (Mrs)

2
IP Address
3
IP Address Grouping
4
Routed and Routing Protocols
  • Consider that a packet needs to be sent from node
    A to node F. How would it decide which path to
    take?

5
Routing Protocol vs Routed Protocol
  • A routed protocol
  • defines the end to end addressing and the packet
    format of a packet that is forwarded between
    nodes on different networks.
  • Internet Protocol (IP) is a routed protocol
  • A routing protocol
  • exchanges topology information with adjacent
    routers to update and maintain their routing
    tables.
  • selects the best path through a network
  • RIP is a routing protocol

6
Routed Protocol
  • A protocol is a set of rules
  • A routed protocol is a set of rules that
    determines how computers at the source and
    destination communicate with each other across
    networks
  • packet format
  • end to end addressing
  • In order for a protocol to be routable, it must
    provide the ability to assign both a network
    number and a host number for each individual
    device.

7
Internet Protocol IP
  • IP is a connectionless, unreliable, best-effort
    delivery protocol
  • As information flows down the layers of the OSI
    model, the data is processed at each layer.
  • IP accepts whatever data is passed down to it
    from the upper layers.

8
IP Packet Header
9
Network Layer Devices in Data Flow
10
Network Layer Devices in Data Flow
  • As a frame is received at a router interface.
  • The MAC address is checked to see if the frame is
    directly addressed to the router interface, or a
    broadcast.
  • The frame header and trailer are removed and the
    packet is passed up to Layer 3.
  • The destination IP address is compared to the
    routing table to find a match.
  • The packet (datagram) is placed in a new frame
    with the MAC address of the next hop interface.
  • The frame is then transmitted.

If a match is found or there is a default route,
the packet will be sent to the interface
specified in the matched routing table statement
otherwise packet is discarded
11
Packets Travel Across Links in a Frame
  • Packets NEVER travel through the network they
    are carried within frames
  • A new frame MUST be created to carry the packet
    over each individual link
  • Routers provide the IP address of the next hop
    interface (router or host)
  • The ARP table provides the MAC address of this IP
    address for the frame destination

12
Router Protocol Stripping
13
Connectionless Network Services
14
Telephone Calls Connection-oriented
15
Connectionless vs. Connection-Oriented
  • In a connection oriented system is established
    between the sender and the recipient before any
    data is transferred.
  • example Telephone
  • In a connectionless system, the destination is
    not contacted before a packet is sent.
  • example Postal system
  • TCP is connection oriented
  • IP is connectionless

16
Connectionless Network Services
  • The Internet is a huge network where packets are
    routed according to their IP addresses.
  • IP is unreliable and best-effort as IP does not
    verify that the data reached its destination and
    therefore does not resend missing packets.
  • Reliability and resending of packets is handled
    by the upper layer protocols.
  • IP may be used in conjunction with TCP to add a
    Layer 4, connection-oriented service that checks
    for missing segments and resends them to provide
    reliability.

17
The IPv4 Packet Header
Time-to-live (TTL) Count Decreases with every
hop This prevents packets from looping endlessly.
18
  • Routing

19
The Network Layer
20
Routing
  • Routing is an OSI Layer 3 function.
  • Routers connect networks (or subnetworks)
  • Routing is the process of finding the most
    efficient path from one device to another
    (router)
  • Routers must maintain routing tables and make
    sure other routers know of changes in the network
    topology. This function is performed using a
    routing protocol to communicate network
    information with other routers

21
Routing Through a Network
  • A router is a network layer device that uses one
    or more routing metrics to determine the optimal
    path through the network

22
Routing Metrics
23
Data Encapsulation
24
Layer 3 Routing and Layer 2 Switching
25
Routers Reduce the Size of Broadcast Domains
  • Routers block LAN broadcasts, so a broadcast
    storm only affects the broadcast domain from
    which it originated
  • Switched networks do not block broadcasts

26
Routing and Switching in a Network
27
Layer 2 Switching and Layer 3 Routing
28
The Routing Process
29
ARP Tables and Routing Tables
30
Router and Switch Features Comparison
31
  • The difference between a routed and routing
    protocol revisited

32
Routed Protocol
33
Routing Protocol
34
Routed Vs Routing protocols
  • A Routed Protocol
  • A network protocol suite that provides enough
    information in its network layer address to allow
    a router to forward it to the next device and
    ultimately to its destination.
  • Defines the format and use of the fields within
    a packet.
  • The Internet Protocol (IP) and Novell's
    Internetwork Packet Exchange (IPX), DECnet,
    AppleTalk, Banyan VINES, and Xerox Network
    Systems (XNS)
  • A Routing Protocol
  • Provides processes for sharing route
    information. Exchange topology info. To
    determining the best routing paths and
    transporting packets through an internetwork
  • Also allows routers to communicate with other
    routers to update and maintain the routing
    tables.
  • Routing Information Protocol (RIP), Interior
    Gateway Routing Protocol (IGRP), Open Shortest
    Path First (OSPF), Border Gateway Protocol (BGP),
    and Enhanced IGRP (EIGRP).

35
  • Back to Routing

36
Path Determination
37
Path Determination
38
Routing Tables
  • Routing tables contain the best routes to all
    known networks.
  • These routes can be either
  • Static routes, which are entered manually by the
    system administrator
  • Or dynamic routes, which are constructed from
    information passed between adjacent routers.
  • A routing table entry contains
  • Each Destination
  • The next hop IP address to reach that
    destination
  • The metric for the route via that next hop
  • Outbound router interface for the next hop

39
Routing Tables
40
Routing Algorithms and Metrics
41
Routing Algorithms and Metrics
  • Routing protocols have one or more of the
    following design goals
  • Optimization
  • Simplicity and low overhead
  • Robustness and stability
  • Flexibility
  • Rapid convergence

42
Routing Algorithms and Metrics
43
Interior and Exterior Gateway Protocols
44
Interior and Exterior Gateway Protocols
  • IGPs route data within an autonomous system.
  • RIP, RIPv2, IGRP, EIGRP, OSPF, IS-IS
  • EGPs route data between autonomous systems
  • Border Gateway Protocol (BGP)

45
Interior Gateway Routing Protocols
  • Link State and Distance Vector Routing Protocols
  • Examples of distance-vector protocols
  • Routing Information Protocol (RIP)
  • Interior Gateway Routing Protocol (IGRP)
  • Enhanced IGRP (EIGRP)
  • Examples of link-state protocols
  • Open Shortest Path First (OSPF)
  • Intermediate System-to-Intermediate System (IS-IS)

46
  • Mechanics of Subnetting

47
Subnetting
  • Reasons for subnetting
  • Provides addressing flexibility for the network
    administrator.
  • Each LAN must have its own network or subnetwork
    address.
  • Provides broadcast containment and low-level
    security on the LAN.
  • Provides some security since access to other
    subnets is only available through the services of
    a router.

48
IP Address Bit Patterns
49
Introduction to Subnetting
  • Host bits must are reassigned (or borrowed) as
    network bits.
  • The starting point is always the leftmost host
    bit.

3 bits borrowed allows 23-2 or 6 subnets
5 bits borrowed allows 25-2 or 30 subnets
12 bits borrowed allows 212-2 or 4094 subnets
50
Subnetting Chart (Bit Position and Value)
51
Subnetting Chart (Subnet Mask Identifier)
52
Subnetting
53
Subnetting Chart
54
Subnetting Example
  • This is an example of subnetting the 192.168.10.0
    class C network into 8 subnets with 32 host
    addresses per subnet
  • Note that the first and last subnets are not used
    (the first can be)
  • Also the first and last host address in each
    subnet are not used

55
Example Host IP Address from Subnet 2
  • The subnet mask is ANDed with the packet address
    to determine the subnet address - as shown in the
    next slides

56
The Logical ANDing Process
57
The Logical ANDing Process
58
Class A and B Hosts
59
Calculating the Subnet ID
60
Subnet Mask Defines the Number of Subnets
61
Find the Subnet Mask
62
Summary
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