Module 3:Designing IP Addressing

Module Overview

• Designing an IPv4 Addressing Scheme

• Designing DHCP Implementation

• Designing DHCP Configuration Options

• Designing an IPv6 Addressing Scheme

• Designing an IPv6 Transition

Lesson 1: Designing an IPv4 Addressing Scheme

• Considerations for Determining Hosts per Subnet

• Considerations for Determining Number of Subnets

• Guidelines for Designing IPv4 Addressing

Considerations for Determining Hosts per Subnet

When determining the number of hosts per subnet, consider:

• All devices on each subnet, including routers

• Network design specifications

• Router and switch performance

• Future growth

The 2n-2 method to determine host bits required for hosts

Considerations for Determining Number of Subnets

When determining the number of subnets, consider:

• WAN locations

Security zones within each location

• Capacity on each segment

• Future growth

The 2n method to determine the number of bits required for subnets

Guidelines for Designing IPv4 Addressing

Use classless routing protocols

Use variable-length subnetting to divide IP ranges

Use supernetting to combine IP ranges

Use public addresses only when a host needs to be connected directly to the Internet

Use classless IP addressing

Use private addresses if you use an indirect connection to the Internet, such as a proxy server or NAT

Lesson 2: Designing DHCP Infrastructure

• Options for Automatic IP Address Assignment

• DHCP Communication Process

• Design Options for DHCP Server

• Methods for Improving DHCP Server Availability

• Securing DHCP Servers

• Guidelines for Designing DHCP Infrastructure

Options for Automatic IPv4 Address Assignment

Option Description

DHCP • IP address and configuration options are delivered by a DHCP server

APIPA• Generates a 169.254.x.x address when a DHCP

server cannot be contacted

• Not suitable for domains or Internet access

Alternate IP • Uses an alternate configuration with options

when a DHCP server cannot be contacted

• Useful for roaming users in some cases

DHCP Communication Process

• DHCP clients and servers communicate with broadcast messages

Broadcast messages by default do not cross routers

• By default, a DHCP server is required on each subnet

• Use DHCP relays to allow a centralized DHCP server to service DHCP clients

Methods for Improving DHCP Server Availability

Redundancy option Details

Split scope

• Divides DHCP scopes between multiple DHCP servers

• 80:20 rule: one DCHP server provides 80% of the address range; the second server provides 20%

Failover clustering

• Allows two or more physical servers to be managed as a single, logical server

• Clustering enables a local method of failover, which achieves greater fault tolerance

Standby server • Gets activated only when need arises

• Requires manual administration to ensure failover

Securing DHCP Servers

DHCP authorization:

Prevents unauthorized Windows servers from running the DHCP service

Does not stop rogue DHCP servers running other operating systems

Enterprise Administrators can authorize a DHCP server

Windows-based groups:

DHCP Administrators local group has permission to configure DHCP servers

Server Operators and Administrators can also configure DHCP servers

DHCP Users local group has permission to read DHCP server configuration

Guidelines for Designing DHCP Infrastructure

In virtualization scenarios, consider using the internal DHCP server

For a combined DHCP infrastructure, base DHCP server locations on the physical characteristics of the LAN or WAN infrastructure

Provide high availability for DHCP

Limit each DHCP server to 1,000 scopes

DHCP servers have low resource utilizationand are good candidates for virtualization

Lesson 3: Designing DHCP Configuration Options

• Using Superscopes in DHCP Infrastructure

• Using Reservations in DHCP Infrastructure

Superscopes in DHCP Infrastructure

Superscopes: Are used when two subnets are present on the same

physical segment

Configure the DHCP to recognize the two subnets as a single physical segment

Ensure that only one DHCP response is sent instead of one DHCP response for each subnet

Reduce DHCP-related network traffic

Using Reservations in DHCP Infrastructure

Reservations:

Link a specific IP address with a specific MAC address

Are an alternative to static IP addresses

Are easier to manage and modify than static IP addresses

Can be used for printers to hosts with associated firewall rules

Lesson 4: Designing an IPv6 Addressing Scheme

• Benefits of IPv6

• IPv6 Address Types

• Guidelines for Designing an IPv6 Addressing Scheme

Benefits of IPv6

Some benefits of IPv6 are:

Larger address space

Hierarchical design for routing efficiency

Includes support for IPsec

Includes support for Quality of Service

Stateful and stateless address configuration

New extensible header format that minimizes overhead

Neighbor Discovery replaces ARP broadcasts

IPv6 Address Types

Address Type Description

Global unicast Equivalent to public IPv4 addresses

Link-Local unicast Automatically assigned to each host for communication on the local subnet

Unique local unicast Equivalent to IPv4 private addresses

Site local unicast Similar to unique local but depreciated

Multicast Equivalent to IPv4 multicast with an additional scope option

Anycast A unicast address that has been assigned to multiple computers

Guidelines for Designing an IPv6 Addressing Scheme

Be aware that most older applications do not support IPv6

Use a hierarchical design for routing efficiency

Obtain a global unicast IPv6 address to communicate on the IPv6 Internet

Do not use the global ID of a unique local address for subnetting

Randomly generate the global ID of a unique local address

Use stateless autoconfiguration to simplify address assignment

Use DHCPv6 to assign additional configurationoptions such as DNS servers