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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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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
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Plan / Implement a VLSM Addressing Scheme
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
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Plan / Implement a VLSM Addressing Scheme
Steps in basic subnetting:
Borrow bits from the host side
Add them to the network side
Change mask to reflect additional bits
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Plan / Implement a VLSM Addressing Scheme
Elements of an addressing scheme:
Subnet number
Network address
Host range
Broadcast address
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Plan / Implement a VLSM Addressing Scheme
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
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Plan a Network Using Classless Routingand CIDR
Classless Inter-Domain Routing (CIDR)
Uses address space efficiently
Used for network address aggregation or summarizing
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Plan a Network Using Classless Routingand CIDR
Route summarization:
Use single address to represent group of contiguoussubnets
Occurs at network boundary
Smaller routing table, faster lookups
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Plan a Network Using Classless Routingand CIDR
Discontiguous subnets cause unreliable routing
Avoid separating subnets with a different network
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Plan a Network Using Classless Routingand CIDR
Use routing protocols that support VLSM
Plan subnetting to complement hierarchical design
Disable auto-summarization if necessary
Update router IOS
Allow for future growth
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Configure and Verify Static and DynamicNAT
RFC 1918: private IP address space
Routed internally, never on the Internet
Hides internal addresses from other networks
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Configure and Verify Static and DynamicNAT
Network Address Translation (NAT)
NAT translates internal private addresses into one ormore public addresses
Use on boundary routers
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Configure and Verify Static and DynamicNAT
Static NAT: map single inside local address to singlepublic address
Dynamic NAT: use a pool of public addresses toassign as needed
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Configure and Verify Static and DynamicNAT
Port Address Translation (PAT)
Dynamically translate multiple inside local addresses toone public address
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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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