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Network Addressing
CS.457 Network Design And Management
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Two Key Network-Layer Functions
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Router Architecture Overview
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IP Fragmentation & Reassembly
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IP datagram format
CS.319 Computer Network
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Network Layer Functions
• Addressing
– Each equipment on the path between
source and destination must have an
address
– Internet Addresses
– Assignment of addresses
– Translation between network layer
addresses and other addresses (address
resolution)
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Types of Addresses
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Assignment of Addresses
• Application Layer address (URL)
– For servers only (clients don’t need it)
– Assigned by network managers and placed in configuration
files.
– Some servers may have several application layer addresses
• Network Layer Address (IP address)
– Assigned by network managers, or by programs such as
DHCP, and placed in configuration files
– Every network on the Internet is assigned a range of possible
IP addresses for use on its network
• Data Link Layer Address (MAC address)
– Unique hardware addresses placed on network interface
cards by their manufacturers ( based on a standardized
scheme)
– Servers have permanent addresses, clients usually do not
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Internet Addresses
• Managed by ICANN
– Internet Corporation for Assigned Names and
Numbers
– Manages the assignment of both IP and
application layer name space (domain names)
• Both assigned at the same time and in groups
• Manages some domains directly (e.g., .com, .org, .net)
and
• Authorizes private companies to become domain name
registrars as well
• Example: kasem bundit university
– IP addresses of kbu.ac.th is 203.149.0.3,
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IPv4 Addresses
• 4 byte (32 bit) addresses
– Strings of 32 binary bits
• Dotted decimal notation
– Used to make IP addresses easier to
understand for human readers
• Breaks the address into four bytes and
writes the digital equivalent for each
byte
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Classfull Adressing
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Subnets
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Subnets: Example
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Subnet Masks
• Used to make it easier to separate the subnet
part of the address from the host part.
• Example
– Subnet: 149.61.10.x
– Subnet mask: 255.255.255.0 or in binary
11111111.11111111.11111111.00000000
• Example
– Subnets: 149.61.x.x
– Subnet mask 255.255.0.0 or, in binary:
11111111.11111111.00000000.00000000
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Network and Host Addresses
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A Network with Two Levels of Hierarchy
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A Network with Three Levels of Hierarchy
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IP addresses
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Dynamic Addressing
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Programs for Dynamic Addressing
• Bootstrap Protocol (bootp)
• Dynamic Host Control Protocol (DHCP)
• Different approaches, but same basic operations:
– A program residing in a client establishes connection to
bootp or DHCP server
– A client broadcasts a message requesting an IP address
(when it is turned on and connected)
– Server (maintaining IP address pool) responds with a
message containing IP address (and its subnet mask)
– IP addresses can also be assigned with a time limit (leased
IP addresses)
– When expires, client must send a new request
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DHCP: Dynamic Host Configuration Protocol
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DHCP client-server scenario
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DHCP client-server scenario
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Handling IP Address Depletion
• Variable Length Subnet Mask
(VLSM)and Classless Interdomain
Routing (CIDR)
• Network Address Translation (NAT)
• IPv6
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CIDR: Classless InterDomain Routing
• subnet portion of address of arbitrary
length
• address format: a.b.c.d/x, where x is #
bits in subnet portion of address
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Q: How does network get subnet part of IP address?
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CS.319 Computer Network
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Hierarchical addressing: route aggregation
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CS.319 Computer Network
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NAT: Network Address Translation
• Motivation: local network uses just one IP
address as far as outside world is concerned:
– range of addresses not needed from ISP: just one
IP address for all devices
– can change addresses of devices in local network
without notifying outside world
– can change ISP without changing addresses of
devices in local network
– devices inside local net not explicitly addressable,
visible by outside world (a security plus).
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NAT : Network Address Translation
• Assign private addresses to the internal
systems
• Router translate the addresses
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NAT: Network Address Translation
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NAT: Network Address Translation
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Using Illegal Addresses with NAT
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IPv6 is…
• IP with:
– Larger address fields (128 bits)
– Yes, that’s a VERY big number!
– Smaller number of header fields
– Altered support for header extensions
– Addition of a flow label header field
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IPv6
• What has not changed
– Almost everything!
– IPv6 is a connectionless datagram delivery
service using end-to-end address identifiers
and end-to-end signalling with TCP and
UDP transport services.
• So is IPv4.
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IPv6 Strengths
• Larger Addresses mean no forced Network
Address Translators
– Eliminate NAT architectures as a means of
address scaling
– Allow coherent end-to-end packet delivery
– Improve the potential for use of end-to-end security
tools for encryption and authentication
– Allow for widespread deployment peer-to-peer
applications
• SIP, IMM, …
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What’s good about IPv6
• Larger Address space
– 128 bit: 3.4ื10^38
• IPv6 can not easily solve (same as IPv4);
– (Security,Multicast,Mobile,QoS)
• Re-design to solve the current problems such
as;
–
–
–
–
Routing
Security
Auto-configuration
Plug & Play
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IPv6
• Initial motivation: 32-bit address space
soon to be completely allocated.
• Additional motivation:
– header format helps speed
processing/forwarding
– header changes to facilitate QoS IPv6
datagram format:
– fixed-length 40 byte header
– no fragmentation allowed
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IPv6 Header (Cont)
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Ipv6 and IPv4 Header Format
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IPv6 Address
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IPv6 address notation
• Basic rules “:” in every 2 bytes,Hex digits
example
• 3ffe:0501:0008:0000:0260:97ff:fe40:efab
– 3ffe:501:8:0:260:97ff:fe40:efab
– 3ffe:501:8::260:97ff:fe40:feab
• ff02:0000:0000:0000:0000:0000:0000:0001
– ff02:0:0:0:0:0:0:1
– ff02::1
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Transition From IPv4 To IPv6
• Not all routers can be upgraded
simultaneous
– no “flag days”
– How will the network operate with mixed
IPv4 and IPv6 routers?
• Tunneling: IPv6 carried as payload in
IPv4 datagram among IPv4 routers
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Tunneling
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Tunneling
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Tunneling
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Question ?
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