Designing Models for Addressing and Numbering · addressing Design a structured model for...

Department of Computer Science

DCS

COMSATS Institute of Information Technology

Designing Models for Addressing

and Numbering

Rab Nawaz JadoonAssistant Professor

COMSATS IIT, Abbottabad

Pakistan

Telecommunication Network Design (TND)


Addressing and Numbering

Guidelines for Assigning Network Layer Addresses

Network layer addresses should be planned, managed, and documented.

Although an end system can learn its address dynamically,

No mechanisms exist for assigning network or subnet numbers dynamically.

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Simple rules for network layer addressing

Design a structured model for addressing before assigning any addresses.

Leave room for growth in the addressing model.

If you do not plan for growth, you might later have to renumber many devices, which is labor-intensive.

Assign blocks of addresses based on the physical network,

not on group membership, to avoid problems when groups or individuals move.

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Simple rules for network layer addressing

To maximize flexibility and minimize configuration, use dynamic addressing for end systems.

To maximize security and adaptability, use private addresses with Network Address Translation (NAT) in IP environments.

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Using a Structured Model for Network Layer Addressing

A structured model for addressing means that addresses are meaningful, hierarchical, and planned.

IP addresses that include a prefix and host part are structured.

Assigning an IP network number to an enterprise network, then subnetting the network number.

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Structured Model

A clearly documented structured model for addressing facilitates management and troubleshooting.

Structure makes it easier to understand network maps, operate network management software, and recognize devices in protocol analyzer traces and reports.

Structured addresses also facilitates,

Network optimization and security because they make it easier to implement network filters on firewalls, routers, and switches.

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Opposite Model

A lot of companies have no model for addressing.

When there is no model, and addresses are assigned in a haphazard way, the following problems can occur:

Duplicate network and host addresses

Illegal addresses that cannot be routed on the Internet

Not enough addresses in total, or by group

Addressees that cannot be used, and so are wasted

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Administering Addresses by a Central Authority

Early in the addressing design process, you need to answer the following questions about public versus private addresses:

Are public, private, or both address types required?

How many end systems need access to the private network only?

How many end systems need to be visible to the public network?

How will translation between private and public addresses occur?

Where in the network topology will the boundary between private and public addresses exist?

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The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of public IP addresses.

The IANA allocates IP addresses to Regional Internet Registries (RIR).

If you need a large number of public addresses, you will work with one of five RIRs:

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Internet Assigned Numbers Authority (IANA)

• Go to www.arin.net for more information.

American Registry for Internet Numbers (ARIN) serves North

America and parts of the Caribbean.

• Go to www.ripe.net for more information.

RIPE Network Coordination Centre (RIPE NCC) serves

Europe, the Middle East, and Central Asia.

• Go to www.apnic.net for more information.

Asia-Pacific Network Information Centre (APNIC) serves Asia and the Pacific

region.

• Go to www.lacnic.net for more information.

Latin American and Caribbean Internet Addresses Registry

(LACNIC) serves Latin America and parts of the Caribbean.

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http://www.arin.net/

http://www.ripe.net/

http://www.apnic.net/

http://www.lacnic.net/


Internet Assigned Numbers Authority (IANA)

• Go to www.afrinic.net for more information.

African Network Information Centre

(AfriNIC) serves Africa.

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http://www.afrinic.net/



The term provider-independent address space refers to addresses that are assigned directly by one of the RIRs.

In practice, most enterprises do not use addresses from the provider-independent address space.

To become eligible for provider-independent address space, an organization must demonstrate to the RIRs that it will have thousands of Internet-connected hosts.

Therefore, most enterprises work with an Internet service provider (ISP) to obtain public addresses,

in which case their addresses are part of the provider-assigned address space.

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The enterprise uses these addresses for as long as it remains a subscriber of the provider.

Changing to a new provider requires renumbering,

which is one problem with provider-assigned addresses.

Nevertheless, unless you have numerous hosts that need public addressing, you will probably use provider-assigned addresses.

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IP Addressing and Subnetting

For detail information about IP Addressing and Subnetting,

See Lecture 16, on

jadoon956.wordpress.com/networks/

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Using Dynamic Addressing for End Systems

Dynamic addressing reduces the configuration tasks required to connect end systems to an internetwork.

Dynamic addressing also supports users who change offices frequently, travel, or work at home occasionally.

With dynamic addressing, a station can automatically learn the network segment to which it is currently attached, and adjust its network layer address accordingly

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Dynamic addressing was built into legacy desktop protocols such as AppleTalk and Novell NetWare.

The designers of these protocols recognized the need to minimize configuration tasks so that inexperienced users could set up small internetworks.

In recent years, however, the importance of dynamic addressing has been recognized, and most companies use DHCP to minimize configuration tasks for IP end systems.

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Many networks use a combination of static and dynamic addressing.

Static addresses are typically used for servers, routers, and network management systems.

Static addresses are also used at the enterprise edge in the e-commerce, Internet edge, VPN/remote-access, and WAN edge modules of a modular network design.

Dynamic addresses are typically used for end systems, including workstations and IP phones.

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Criteria for using static versus dynamic addressing

The number of end systems:

When there are more than 30 systems, dynamic addressing is usually preferable.

Renumbering:

If it is likely you will need to renumber systems in the future and there are many end systems, dynamic address assignment is the better choice.

Renumbering for public addresses will become necessary if a new ISP is selected.

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High availability:

Statically assigned IP addresses are available anytime.

Dynamically assigned IP addresses have to be acquired from a server first.

If the server fails, an address cannot be acquired. To avoid this problem, you can deploy redundant DHCP servers or use static addresses.

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Security:

With dynamic address assignment, in most cases, any device that connects to the network can acquire a valid address.

This imposes some security risk and might mean that dynamic addressing is not appropriate for a company with a strict security policy.

Address tracking:

If a management or security policy requires that addresses be tracked, static addressing might be easier to implement than dynamic addressing.

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Department of Computer Science 21

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Designing Models for Addressing and Numbering · addressing Design a structured model for...

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