Discovery Routing Switching Chapter4

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2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE I Chapter 6 1

Addressing in an

Enterprise Network

Introducing Routing and Switching in the Enterprise Chapter 4


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2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE 1 Chapter 6 2

Objectives

Analyze the features and benefits of a hierarchical IPaddressing structure.

Plan and implement a VLSM IP addressing scheme.

Plan a network using classless routing and CIDR.

Configure and verify both static and dynamic NAT.


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Features & Benefits of a Hierarchical IPAddressing Structure

Flat networks with a single broadcast domain loseefficiency as hosts are added

Two solutions:

Create VLANs

Use routers in a hierarchical network design


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Features & Benefits of a Hierarchical IPAddressing Structure

Classful network address in the Core Layer

Successively smaller subnets in the Distribution andAccess Layers


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Plan / Implement a VLSM Addressing Scheme

Subnet mask: 32-bit value Distinguishes between network and host bits

Can vary in length to accommodate number of hosts onLAN segment


7/22 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE 1 Chapter 6 7


Boolean ANDing compares bits in host address to bits

in subnet mask

1 and 1 = 1

1 or 0 and 0 = 0

Resulting value is network address




Steps in basic subnetting:

Borrow bits from the host side

Add them to the network side

Change mask to reflect additional bits




Elements of an addressing scheme:

Subnet number

Network address

Host range

Broadcast address




Benefits of Variable Length Subnet Masks (VLSM):

Flexibility

Efficient use of address space

Ability to use route summarization


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Plan a Network Using Classless Routingand CIDR

Classful routing

Default subnet masks

Class determined by firstoctet

No subnet maskinformation exchanged inrouting updates

Classless routing

Network prefix

Slash (/) mask

Subnet mask informationexchanged in routingupdates




Classless Inter-Domain Routing (CIDR)

Uses address space efficiently

Used for network address aggregation or summarizing




Route summarization:

Use single address to represent group of contiguoussubnets

Occurs at network boundary

Smaller routing table, faster lookups




Discontiguous subnets cause unreliable routing

Avoid separating subnets with a different network




Use routing protocols that support VLSM

Plan subnetting to complement hierarchical design

Disable auto-summarization if necessary

Update router IOS

Allow for future growth



Configure and Verify Static and DynamicNAT

RFC 1918: private IP address space

Routed internally, never on the Internet

Hides internal addresses from other networks




Network Address Translation (NAT)

NAT translates internal private addresses into one ormore public addresses

Use on boundary routers




Static NAT: map single inside local address to singlepublic address

Dynamic NAT: use a pool of public addresses toassign as needed




Port Address Translation (PAT)

Dynamically translate multiple inside local addresses toone public address



Summary

Hierarchical network design groups users into subnets

VLSM enables different masks for each subnet

VLSM requires classless routing protocols

CIDR network addresses are determined by prefixlength

Route summarization, route aggregation, orsupernetting, is done on a boundary router

NAT translates private addresses into public addressesthat route over the Internet

PAT translates multiple local addresses into a singlepublic address


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Documents

Discovery Routing Switching Chapter4