ITEC 275
Computer Networks – Switching,
Routing, and WANs
Week 6
Robert D’Andrea
Some slides provide by Priscilla
Oppenheimer and used with permission
Agenda
• Learning Activities
– IP Addressing
– Static and Dynamic Assignment
– IPv6
– IPv4 to IPv6 Transition Methods
Guidelines for Addressing and Naming
• Use a structured model for addressing and
naming
• Assign addresses and names hierarchically
• Decide in advance if you will use
– Central or distributed authority for addressing
and naming
– Public or private addressing
– Static or dynamic addressing and naming
Advantages of Structured Models for
Addressing & Naming
• It makes it easier to
– Read network maps
– Operate network management software
– Recognize devices in protocol analyzer traces
– Meet goals for usability
– Design filters on firewalls and routers
– Implement route summarization
Public IP Addresses
• Managed by the Internet Assigned Numbers
Authority (IANA)
• Users are assigned IP addresses by Internet
service providers (ISPs).
• ISPs obtain allocations of IP addresses from
their appropriate Regional Internet Registry
(RIR)
Regional Internet Registries (RIR)
• American Registry for Internet Numbers (ARIN) serves
North America and parts of the Caribbean.
• RIPE Network Coordination Centre (RIPE NCC) serves
Europe, the Middle East, and Central Asia.
• Asia-Pacific Network Information Centre (APNIC) serves
Asia and the Pacific region.
• Latin American and Caribbean Internet Addresses
Registry (LACNIC) serves Latin America and parts of the
Caribbean.
• African Network Information Centre (AfriNIC) serves
Africa.
Criteria for Using Static Vs. Dynamic
Addressing
•
•
•
•
•
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The number of end systems
The likelihood of needing to renumber
The need for high availability
Security requirements
The importance of tracking addresses
Whether end systems need additional
information
– (DHCP can provide more than just an address)
The Two Parts of an IP Address
32 Bits
Prefix
Prefix Length
Host
Prefix Length
• An IP address is accompanied by an indication
of the prefix length
– Subnet mask
– /Length
• Examples
– 192.168.10.1 255.255.255.0
– 192.168.10.1/24
Subnet Mask
• 32 bits long
• Specifies which part of an IP address is the
network/subnet field and which part is the host field
– The network/subnet portion of the mask is all 1s in binary.
– The host portion of the mask is all 0s in binary.
– Convert the binary expression back to dotted-decimal
notation for entering into configurations.
• Alternative
– Use slash notation (for example /24)
– Specifies the number of 1s
Subnet Mask Example
• 11111111 11111111 11111111 00000000
• What is this in slash notation?
• What is this in dotted-decimal notation?
Subnet Mask Example
• 11111111 11111111 11111111 00000000
• What is this in slash notation?
– /24
• What is this in dotted-decimal notation?
– 255.255.255.0
Another Subnet Mask Example
• 11111111 11111111 11110000 00000000
• What is this in slash notation?
• What is this in dotted-decimal notation?
Another Subnet Mask Example
• 11111111 11111111 11110000 00000000
• What is this in slash notation?
– /20
• What is this in dotted-decimal notation?
– 255.255.240.0
One More Subnet Mask Example
• 11111111 11111111 11111000 00000000
• What is this in slash notation?
• What is this in dotted-decimal notation?
One More Subnet Mask Example
• 11111111 11111111 11111000 00000000
• What is this in slash notation?
– 21
• What is this in dotted-decimal notation?
– 255.255.248.0
Private and Public Addresses
Figure 6-1
NAT
• Static
– One private address to one public address
– Used for servers that must be visible to the public
network
• Dynamic
– Many unregistered addresses to one registered
address from a pool of addresses
– Used for workstations that only connect to the public
network when required
• Combination
– Used by most organizations
NAT Demonstration
Internet Protocol, Src Addr: 192.168.0.8 (192.168.0.8), Dst Addr: 207.46.249.189 (207.46.249.189)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 295
Identification: 0x9a25 (39461)
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 128
Protocol: TCP (0x06)
Header checksum: 0xd60e (correct)
Source: 192.168.0.8 (192.168.0.8)
Destination: 207.46.249.189 (207.46.249.189)
Transmission Control Protocol, Src Port: 1137 (1137), Dst Port: 80 (80), Seq: 1, Ack: 1, Len: 255
Source port: 1137 (1137)
Destination port: 80 (80)
Sequence number: 1
Address use in the Enterprise
Figure 6-3
Designing Networks with Subnets
• Determining subnet size
• Computing subnet mask
• Computing IP addresses
Determinations
• How many locations?
– How many segments are required?
• How many devices?
– How large must each segment be?
• What are the IP addressing requirements for
each location?
– Is public access required?
• What subnet size is appropriate?
– Determined by first and second questions
Addresses to Avoid When Subnetting
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•
•
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A node address of all ones (broadcast)
A node address of all zeros (network)
A subnet address of all ones (all subnets)
A subnet address of all zeros (confusing)
– Cisco IOS configuration permits a subnet
address of all zeros with the ip subnet-zero
command
Practice
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•
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Network is 172.16.0.0
You want to divide the network into subnets.
You will allow 600 nodes per subnet.
What subnet mask should you use?
What is the address of the first node on the
first subnet?
• What address would this node use to send to
all devices on its subnet?
Practice
• Network is 172.16.0.0
• You want to divide the network into subnets.
– 64
• You will allow 600 nodes per subnet.
– 1022
• What subnet mask should you use?
– 255.255.252.0 (/22)
• What is the address of the first node on the first subnet?
– 172.16.0.1
• What address would this node use to send to all devices on
its subnet?
– 172.16.3.255
More Practice
• Network is 172.16.0.0
• You have eight LANs, each of which will be
its own subnet.
• What subnet mask should you use?
• What is the address of the first node on the
first subnet?
• What address would this node use to send
to all devices on its subnet?
More Practice
• Network is 172.16.0.0
• You have eight LANs, each of which will be its own
subnet.
• What subnet mask should you use?
– 255.255.224.0 (/19)
• What is the address of the first node on the first
subnet?
– 172.16.0.1
• What address would this node use to send to all devices
on its subnet?
– 172.16.31.255
One More
•
•
•
•
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Network is 192.168.55.0
You want to divide the network into subnets.
You will have approximately 25 nodes per subnet.
What subnet mask should you use?
What is the address of the last node on the last
subnet?
• What address would this node use to send to all
devices on its subnet?
One More
• Network is 192.168.55.0
• You want to divide the network into subnets.
– 8
• You will have approximately 25 nodes per subnet.
– 30
• What subnet mask should you use?
– 255.255.255.224 (/27)
• What is the address of the last node on the last subnet?
– 192.168.255.254
• What address would this node use to send to all devices on
its subnet?
– 192.168.255.255
IP Address Classes
• Classes are now considered obsolete
• But you have to learn them because
– Everyone in the industry still talks about them!
– You may run into a device whose configuration is
affected by the classful system
Classful IP Addressing
Class
First
Few Bits
First Byte
Prefix
Length
Intent
A
B
C
D
E
0
10
110
1110
1111
1-126*
128-191
192-223
224-239
240-255
8
16
24
NA
NA
Very large networks
Large networks
Small networks
IP multicast
Experimental
*Addresses starting with 127 are reserved for IP traffic local to a host.
Division of the Classful Address Space
Class
Prefix
Length
Number of Addresses
per Network
A
B
C
8
16
24
224-2 = 16,777,214
216-2 = 65,534
28-2 = 254
Classful IP is Wasteful
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•
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Class A uses 50% of address space
Class B uses 25% of address space
Class C uses 12.5% of address space
Class D and E use 12.5% of address space
Classless Addressing
• Prefix/host boundary can be anywhere
• Less wasteful
• Supports route summarization
– Also known as
•
•
•
•
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Aggregation
Supernetting
Classless routing
Classless inter-domain routing (CIDR)
Prefix routing
Supernetting
172.16.0.0
172.17.0.0
172.18.0.0
Branch-Office Router
172.19.0.0
Branch-Office Networks
•
•
Move prefix boundary to the left
Branch office advertises 172.16.0.0/14
Enterprise Core
Network
Addressing Hierarchy
Figure 6-6 – Page 387
Route summarization
• Summary 192.168.0/21
Figure 6-5 – Page 386
172.16.0.0/14 Summarization
Second Octet in Decimal
Second Octet in Binary
16
00010000
17
00010001
18
00010010
19
00010011
Private Addressing
• 10.0.0.0 – 10.255.255.255
• 172.16.0.0 – 172.31.255.255
• 192.168.0.0 – 192.168.255.255
Discontiguous Subnets
Area 0
Network
192.168.49.0
Router A
Area 1
Subnets 10.108.16.0 10.108.31.0
Router B
Area 2
Subnets 10.108.32.0 10.108.47.0
A Mobile Host
Router A
Router B
Subnets 10.108.16.0 10.108.31.0
Host 10.108.16.1
IPv6
• A technology developed to overcome the
limitations of the current standard, IPv4
• Combines expanded addressing with a more
efficient and feature-rich header to improve
scaling
• Satisfies the increasingly complex
requirements of hierarchical addressing that
IPv4 does not support
IPv6 Features
• Larger address space:
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–
–
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IPv6 addresses are 128 bits, compared to IPv4's 32 bits
Allows more support for addressing hierarchy levels
A much greater number of addressable nodes
Simpler auto-configuration of addresses
• Globally unique IP addresses:
– Every node can have a unique global IPv6 address
– Eliminates the need for NAT.
• Site multi-homing:
– IPv6 allows hosts to have multiple IPv6 addresses
– Allows networks to have multiple IPv6 prefixes
– Sites can have connections to multiple ISPs without breaking the
global routing table
IPv6 Features (continued)
• Header format efficiency:
– A simplified header with a fixed header size makes processing more efficient.
• Improved privacy and security:
– IPsec is the IETF standard for IP network security, available for both IPv4 and
IPv6. Although the functions are essentially identical in both environments,
IPsec is mandatory in IPv6. IPv6 also has optional security headers.
• Flow labeling capability:
– A new capability enables the labeling of packets belonging to particular traffic
flows for which the sender requests special handling, such as nondefault
quality of service (QoS) or real-time service.
• Increased mobility and multicast capabilities:
– Mobile IPv6 allows an IPv6 node to change its location on an IPv6 network and
still maintain its existing connections. With Mobile IPv6, the mobile node is
always reachable through one permanent address. A connection is established
with a specific permanent address assigned to the mobile node, and the node
remains connected no matter how many times it changes locations and
addresses
IPv6 Address Format
• The format is x:x:x:x:x:x:x:x, where x is a 16-bit
hexadecimal field
– 2035:0001:2BC5:0000:0000:087C:0000:000A
• Leading 0s within each set of four hexadecimal digits
can be omitted, and a pair of colons (::) can be used,
once within an address, to represent any number of
successive 0s.
– 2035:1:2BC5::87C:0:A
IPv6 Addresses
• Link-local address: The host configures its own link-local address
autonomously, using the link-local prefix FE80::0/10 and a 64-bit identifier
for the interface, in an EUI-64 format.
• Stateless autoconfiguration: A router on the link advertises—either
periodically or at the host's request—network information, such as the 64bit prefix of the local network and its willingness to function as a default
router for the link. Hosts can automatically generate their global IPv6
addresses by using the prefix in these router messages; the hosts do not
need manual configuration or the help of a device such as a DHCP server.
• Stateful using DHCP for IPv6 (DHCPv6): DHCPv6 is an updated version of
DHCP for IPv4. DHCPv6 gives the network administrator more control than
stateless autoconfiguration and can be used to distribute other
information, including the address of the DNS server. DHCPv6 can also be
used for automatic domain name registration of hosts using a dynamic
DNS server. DHCPv6 uses multicast addresses.
IPv6 Aggregatable Global Unicast
Address Format
3
13
8
FP
TLA
ID
RES
24
NLA
ID
Public topology
•
•
•
•
•
•
FP
TLA ID
RES
NLA ID
SLA ID
Interface ID
16
SLA
ID
64 bits
Interface ID
Site
Topology
Format Prefix (001)
Top-Level Aggregation Identifier
Reserved for future use
Next-Level Aggregation Identifier
Site-Level Aggregation Identifier
Interface Identifier
Upgrading to IPv6
• Dual stack
• Tunneling
• Translation
Dual-Stack
A dual-stack node enables both IPv4 and
IPv6 stacks. Applications communicate
with both IPv4 and IPv6 stacks; the IP
version choice is based on name lookup
and application preference. This is the
most appropriate method for campus
and access networks during the
transition period, and it is the preferred
technique for transitioning to IPv6. A
dual-stack approach supports the
maximum number of applications.
Figure 6-24
Tunneling
Figure 2-25
Translation
Dual-stack and tunneling techniques
manage the interconnection of IPv6
domains. For legacy equipment that
will not be upgraded to IPv6 and for
some deployment scenarios,
techniques are available for
connecting IPv4-only nodes to
IPv6-only nodes, using translation,
an extension of NAT techniques.
Guidelines for Assigning Names
• Names should be
– Short
– Meaningful
– Unambiguous
– Distinct
– Case insensitive
• Avoid names with unusual characters
– Hyphens, underscores, asterisks, and so on
Domain Name System (DNS)
• Maps names to IP addresses
• Supports hierarchical naming
– example: frodo.rivendell.middle-earth.com
• A DNS server has a database of resource records
(RRs) that maps names to addresses in the server’s
“zone of authority”
• Client queries server
– Uses UDP port 53 for name queries and replies
– Uses TCP port 53 for zone transfers
DNS Details
• Client/server model
• Client is configured with the IP address of a
DNS server
– Manually or DHCP can provide the address
• DNS resolver software on the client machine
sends a query to the DNS server. Client may
ask for recursive lookup.
DNS Recursion
• A DNS server may offer recursion, which allows the
server to ask other servers
– Each server is configured with the IP address of one or more
root DNS servers.
• When a DNS server receives a response from another
server, it replies to the resolver client software. The
server also caches the information for future requests.
– The network administrator of the authoritative DNS server for a
name defines the length of time that a non-authoritative server
may cache information.
Summary
• Use a systematic, structured, top-down
approach to addressing and naming
• Assign addresses in a hierarchical fashion
• Distribute authority for addressing and
naming where appropriate
• IPv6 looms in our future
Review Questions
• Why is it important to use a structured model
for addressing and naming?
• When is it appropriate to use IP private
addressing versus public addressing?
• When is it appropriate to use static versus
dynamic addressing?
• What are some approaches to upgrading to
IPv6?
This Week’s Outcomes
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IP Addressing
Static and Dynamic Assignment
IPv6
IPv4 to IPv6 Transition Methods
Due this week
• 5-1 – Concept questions 4
• 1-5-1 – Network design project
– Switches
Next week
• Read chapters 7 in
Top-Down Network Design
• 6-1 – Concept questions 5
• FranklinLive session 7
Q&A
• Questions, comments, concerns?