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CIS460

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CIS460 NETWORK ANALYSIS AND DESIGN CHAPTER 6 Designing Models for Addressing and Naming Overview Look at the guidelines for assigning addresses and names to ... – PowerPoint PPT presentation

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Title: CIS460


1
CIS460 NETWORK ANALYSIS AND DESIGN
  • CHAPTER 6
  • Designing Models for Addressing and Naming

2
Overview
  • Look at the guidelines for assigning addresses
    and names to internetwork components, including
    networks, subnets, routers, servers, and end
    systems
  • Importance of using a structured model for
    network layer addressing and naming
  • Importance of developing policies and procedures
    for addressing and naming

3
Guidelines for Assigning Network-Layer Address
  • Should be planned, managed and documented
  • Rules for network-layer addressing
  • Design a structured model
  • Leave room for growth
  • Assign blocks of addresses in a hierarchical
    fashion
  • Use meaningful numbers
  • Delegate authority if possible to regional/branch
  • use dynamic addressing
  • use private addresses with network address
    translation

4
Using a Structured Model for Network-Layer
Addressing
  • Addresses are meaningful, hierarchical, and
    planned
  • A clearly documented structured model facilitates
    management and troubleshooting
  • With no model problems can occur
  • Duplicate network and host addresses
  • illegal addresses that cannot route on internet
  • insufficient addresses
  • addresses that cannot be used

5
Using Meaningful Network Numbers
  • In AppleTalk assign cable range for each network
    segment
  • e.g., building number/floor number
  • In Novell NetWare each network segment is
    assigned a 4-byte hexadecimal number
  • Using building and floor numbers allow
    identifying and narrowing location of problems

6
Administering Addresses by a Central Authority
  • Corporate IS or enterprise network department
    should develop a global model for network-layer
    addressing
  • In an IP environment can request block of numbers
    from an ISP or Internet Assigned Numbers
    Authority
  • If from ISP request a large enough block for
    scalability
  • Use private addresses as an alternative

7
Distributing Authority for Addressing
  • Determine who is to implement model
  • if inexperienced networks administrators then
    keep it simple
  • If branch/regional offices inexperienced then
    keep authority centralized

8
Using Dynamic Addressing for End Systems
  • Reduces the configuration tasks required to
    connect end systems
  • Supports users who change offices frequently
  • Built into desktop protocols such as AppleTalk
    and Novell NetWare
  • Minimizes configuration tasks

9
AppleTalk Dynamic Addressing
  • Network layer stations address consists of a
    16-bit network number and an 8-bit node ID
  • Once network-layer address is chosen it is saved
    in battery-backed-up RAM so it doesnt have to
    get new address each time it boots
  • AppleTalk station communicates with a router to
    determine the cable range for its network segment

10
Novell NetWare Dynamic Addressing
  • Station address consists of 4 byte network number
    and a 6-byte node ID.
  • 6-byte node ID is the same as the stations MAC
    address
  • A network manage configures routers and servers
    on a NetWare network with the 4 byte network
    number for a network segments

11
IP Dynamic Addressing
  • An IP layer address is 4 bytes in length and
    consists of a prefix and host part
  • In the past each host was required to be
    configured manually. Now addressing is done
    dynamically through
  • Reverse Address Resolution Protocol (RARP) and
    BOOTP
  • BOOTP is more sophisticated than RARP and returns
    additional information including address of
    default router

12
The Dynamic Host Configuration Protocol (DHCP)
  • DHCP is based on BOOTP
  • BOOTP hosts interoperate with DHCP
  • DHCP adds many enhancements to BOOTP including
    larger vendor specific information field and
    automatic allocation of reusable network-layer
    address
  • DHCP uses a client/server model
  • Servers allocate network-layer addresses and save
    information about which addresses are used

13
The Dynamic Host Configuration Protocol (DHCP)
(Contd)
  • DHCP supports three methods for IP address
    allocation
  • Automatic allocation - assigns permanent IP
    address to a client
  • Dynamic allocation - assigns an IP address to a
    client for a limited period of time
  • Manual - network administrator assigns
    permanently and DHCP merely conveys address
    information

14
The Dynamic Host Configuration Protocol (DHCP)
(Contd)
  • Dynamic is most popular where hosts are not on
    all of the time. Address given for a short
    period time called a lease
  • Can reuse address if lease has expired
  • Chen client boots it broadcasts a DHCP discover
    message on its local subnet
  • each server responds with a DHCP offer message

15
The Dynamic Host Configuration Protocol (DHCP)
(Contd)
  • Client choose one server response to request
    configuration parameters
  • Server selected commits configuration parameters
    to persistent storage and responds with DHCP ACK
    message
  • If no response received client times out and
    resends a DHCP discover and request messages

16
Using Private Addresses in an IP Environment
  • These are addresses assigned by internal networks
    and hosts without any coordination from an ISP or
    the Internet Assigned Numbers Authority
  • An advantage is security. Private numbers are
    not advertised on the Internet
  • Helps meet goals for adaptability and flexibility

17
Using Private Addresses in an IP Environment
(Contd)
  • Network can advertise just one network number or
    small block of numbers to the Internet
  • Can reserve scarce Internet addresses for public
    servers

18
Caveats with Private Addressing
  • Outsourcing network management is difficult
  • Difficulty of communicating with partners,
    vendors, suppliers, and other outsiders
  • Easy to forget to use a structured model
  • Assign in a structured, hierarchical fashion

19
Network Address Translation (NAT)
  • An IP mechanism that is used for converting
    addresses from an inside network to addresses
    that are appropriate for an outside network and
    vice-versa
  • NAT administrator configures a pool of outside
    addresses that can be used for translation

20
Network Address Translation (NAT) (Contd)
  • Some NAT products offer port translation for
    mapping several addresses to the same address
  • When using NAT all traffic must go through a NAT
    gateway
  • Must also modify IP addresses that occur inside
    the data part of a packet

21
Using a Hierarchical Model for Assigning Addresses
  • Hierarchical addressing is a model for applying
    structure to addresses so that numbers in the
    left part of an address refer to large blocks of
    networks or nodes, and numbers in the right part
    of an address refer to individual networks or
    nodes

22
Why Use a Hierarchical Model for Addressing and
Routing
  • Support for easy troubleshooting, upgrades and
    manageability
  • Optimized performance
  • Faster routing-protocol convergence
  • Scalability
  • Stability
  • Fewer network resources need

23
Why Use a Hierarchical Model for Addressing and
Routing (Contd)
  • Permits summarization (aggregation) of network
    numbers
  • Summarization allows a router to group many
    network numbers when advertising its routing
    table
  • Facilitates variable-length subnet masking (VLSM)

24
Hierarchical Routing
  • Means that knowledge of the network topology and
    configuration is localized
  • No single router needs to understand how to get
    to each other network segment
  • Addresses must be assigned in hierarchical fashion

25
Classless Inter-Domain Routing
  • The internet has a severe scalability problem
  • Classless inter_domain Routing (CIDR) is a method
    for summarizing routes
  • Addresses should be assigned in blocks
  • Routers should group routes together to cut down
    on the quantity of routing information shared by
    Internet routers

26
Classless Routing Versus Classful Routing
  • IP address contains a prefix part and a host part
  • Prefix identifies a block of host numbers and is
    used for routing that block
  • Traditional (classful routing) does not transmit
    any information about the prefix length
  • Traditional IP hosts and routers had a limited
    capability to understand prefix lengths and
    subnets

27
Classless Routing Versus Classful Routing (Contd)
  • Classless routing protocols transmit a prefix
    length with an IP address
  • Classless routing protocols include Routing
    Information Protocol (RIP) V2, Enhanced Interior
    Gateway Routing Protocol (Enhanced IGRP), Open
    Shortest Path First (OSPF), Border Gateway
    Routing Protocol (BGP) Intermediate System-to
    Intermediate System (IS-IS)

28
Route Summarization (Aggregation)
  • When advertising routes into another major
    network classful routing protocols automatically
    summarize subnets
  • Only advertise route to a Class A, B, or C
    network instead of routes to subnets
  • Discontiguous subnets are not supported
  • Classless routing protocols advertise a route and
    a prefix length

29
Route Summarization Tips
  • For route summarization to work correctly
  • Multiple IP addresses must share the same
    left-most bits
  • Routers must base their routing decisions on a
    32-bit IP address and prefix length that can be
    up to 32 bits
  • routing protocols must carry the prefix length
    with 32-bit addresses

30
Discontiguous Subnets
  • Subnets must be next to each other to be
    supported
  • Classless routing protocol can be used to route
    to discontiguous subnets

31
Mobile Hosts
  • Classless routing and discontiguous subnets
    support mobile hosts
  • A mobile host is a host that moves from one
    network to another and has a statically-defined
    IP address
  • Routers use the longest prefix available that is
    appropriate for the destination address in the
    packet

32
Variable-Length Subnet Masking
  • Using classless routing means that you can have
    different sizes of subnets within a single
    network
  • Variable length subnet masking (VLSM) relies on
    providing prefix length information explicitly
    with each use of an address
  • It is important to avoid inadvertently
    overlapping blocks of addresses

33
Designing a Model for Naming
  • Short meaningful names enhance user productivity
    and simplify network management
  • A good naming model strengthens the performance
    and availability of a network
  • It should let a user transparently access a
    service by name rather than address
  • The system should map the name to the address

34
Distributing Authority for Naming
  • No department should be burdened with assigning
    and maintaining all names
  • If device has local name server instead of
    depending on a centralized server many names can
    be resolved to addresses locally without causing
    traffic on the internetwork

35
Guidelines for Assigning Names
  • Should be short, meaningful, unambiguous and
    distinct
  • Users should recognize which name goes with which
    device
  • Can use three letter prefixes
  • Some networks use geographical names
  • Avoid names with unusual characters
  • Avoid case sensitivity

36
Assigning Names in an AppleTalk Environment
  • You assign names to shared servers and printers
  • Use meaningful names
  • can also assign names to zones. A zone is a
    collection of nodes that share information

37
Assigning Names in a Novell NetWare Environment
  • Assign names to resources such as volumes on a
    file server, shared printers, print queues,
    printer servers and possibly other servers
  • Generally no need to assign names to end systems

38
Assigning Names in a NetBIOS Environment
  • Is a session-layer protocol that includes
    functions for naming devices which ensures the
    unique of names and finding named services

39
NetBIOS in a Bridged or Switched Environment
(NetBEUI)
  • NetBIOS was originally implemented as session
    layer software that runs on top of the driver for
    a NIC
  • Makes extensive use of broadcast packets for
    naming functions
  • When started it broadcasts check-name queries to
    make sure its name is unique
  • Can have as many as 32 names

40
NetBIOS in a Novell NetWare Environment (NWLink)
  • With NWLink NetBIOS runs on top of Novells
    Sequenced Packet Exchange and Internetwork Packet
    Exchange protocols
  • Uses type-20 broadcast packets to send name
    registration

41
NetBIOS in a TCP/IP Environment (NetBT)
  • In this protocol you have 4 options for name
    registration and lookup
  • Broadcasts - used to announce services
  • Lmhosts files - a lmhosts file is place on each
    station. Not dynamic
  • Windows Internet Name Service (WINS) - use WINS
    server to resolve a name
  • Domain Name System (DNS) - standard internet
    service which uses a generic IP environment

42
Assigning Names in an IP Environment
  • Accomplished by configuring hosts files, DNS
    servers, or Network Information Service (NIS)
    servers.

43
The Domain Name System
  • Developed in early 1980s to manage a hosts file
    containing the names and addresses of all the
    systems on the Internet
  • com, edu, gov, etc
  • Can also include geographical level domains
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