2.22. 5.3.2Designing Models for
Addressing and Numbering
A structuredaddressing 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 a campus network, then subnetting
the network number and subnetting the subnets, is a structured (hierarchical)
model for IP addressing.
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 facilitate network
optimization and security because
2.23. 5.3.2.0 Static and 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 and automation of station or LAN. DHCPprotocol
have minimize configuration tasks for IP end system .In our network we are
using both static and dynamic addressing IP. Static addresses
are used for servers, routers, switches,and printers.
Comparison between static versus dynamic addressing include the
following:
ü The number of end systems devices: When
there are more than 30 systems, dynamic addressingis usually preferable.
ü Renumbering:If it is likely you will need
to renumber systems in the future andthere are many end systems, dynamic
address assignment is the better choice.Renumbering for public addresses will
become necessary if a new ISP is selected. Inaddition, you might plan to
renumber because the current plan is not well structuredor will run out of
numbers soon.
ü High availability: Statically assigned
IP addresses are available anytime. Dynamicallyassigned IP addresses have to be
acquired from a server first. If the server fails, anaddress cannot be
acquired. To avoid this problem, you can deploy redundant DHCPservers or use
static addresses.
ü Security:With dynamic address assignment,
in most cases, any device that connectsto the network can acquire a valid
address. This imposes some security risk.
ü Address tracking: If a management requires that addresses
betracked, static addressing might be easier to implement than dynamic
addressing.
ü Additional parameters: If end systems
need information beyond an address, dynamicaddressing is useful because a
server can provide additional parameters to clientsalong with the address. For
example, a DHCP server provides a subnet mask, a default gateway,
2.24. 5.3.2.1 Hierarchical Routing
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.
Hierarchical routing requires that a network administrator assign
addresses in a hierarchical fashion. IP addressing and routing have been
somewhat hierarchical for a long time, but in recent years, as the Internet and
enterprise intranets have grown, it has become necessary to add more
hierarchy.
Identifies a block of host numbers and is used for routing to
that block. Traditional routing, also known as classful routing, does not
transmit any information about the prefix length. With classful routing, hosts
and routers calculate the prefix length by looking at the first few bits of an
address to determine its class.
Classless routing protocols, on the other hand, transmit a prefix
length with an IP address. This allows classless routing protocols to group
networks into one entry and use the prefix length to specify which networks are
grouped. Classless routing protocols also accept any arbitrary prefix length,
rather than only accepting lengths of 8, 16, or 24, which the classful system
dictated.
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