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Week Eight Agenda. Attendance Announcements Review Week Seven Information Current Week Information Upcoming Assignments. Week Eight Topics. Shortage of IP addresses with IPv4 Private, public, and NAT addressing Static or Dynamic IP Address Assignment

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Week eight agenda
Week Eight Agenda

  • Attendance

  • Announcements

  • Review Week Seven Information

  • Current Week Information

  • Upcoming Assignments

Week eight topics
Week Eight Topics

  • Shortage of IP addresses with IPv4

  • Private, public, and NAT addressing

  • Static or Dynamic IP Address Assignment

  • Hierarchical Addressing, route summarization, CIDR

  • Static and dynamic Domain Name Server (DNS)

  • IPv6 Standard

Ipv4 private addresses
IPv4 Private Addresses

The IPv4 Standard created a problem that was temporarily solved by assigning private addresses within a local network and translating the private addresses to public addresses when Internet connectivity is required.

Ip address design strategy
IP Address Design Strategy

Are there public, private, or both types of addressing required?

How many end systems will need access to the public network? This includes email, file transfer, or web browsing.

How many end systems require access to visible public network(s). This includes e-commerce, such as web servers, database servers, application servers, and public servers. These end systems require globally unambiguous IP addresses.

Where will the boundaries be between private and public IP addresses and how will they be implemented?

Private addresses
Private Addresses

  • RFC 1918 sets aside three blocks of private IP addresses:

  • One (1) Class A address

  • Sixteen (16) Class B addresses

  • Two hundred and fifty six (256) Class C addresses

  • These addresses are for private, internal network use only

  • Packets containing private addresses are not routed over the Internet

  • A router should never route RFC 1918 addresses, because ISPs typically configure the border routers to prevent privately addressed traffic from being forwarded

Private addressing
Private Addressing –

Where does the /12 come from?

12 bits in common

10101100 . 00010000 . 00000000 . 00000000 –

10101100 . 00011111 . 11111111 . 11111111 –


10101100 . 0001000 00000000 . 00000000 –

Network address translation nat
Network Address Translation (NAT)

  • NAT is defined by RFC 1631. It is the process of swapping one address for another in the IP packet header.

  • NAT is a mechanism for conserving registered IP addresses in large networks and simplifying IP addressing management tasks.

  • In practice, NAT is used to allow hosts that are privately addressed, using RFC 1918 addresses, to access the Internet

  • NAT allows many hosts on an inside network to communicate on the Internet with one valid, assigned IP address

Network address translation nat1
Network Address Translation (NAT)

What is NAT Overload?

NAT overloading (sometimes called Port Address Translation or PAT) maps multiple private IP addresses to a single public IP address or a few addresses.This is what most home routers do.

With NAT overloading, multiple addresses can be mapped to one or to a few addresses because each private address is also tracked by a port number. When a client opens a TCP/IP session, the NAT router assigns a port number to its source address. NAT overload ensures that clients use a different TCP port number for each client session with a server on the Interne

Network address translation nat2
Network Address Translation (NAT)

  • Static NAT –an inside address is always translated to the same outside address. Useful when hosts may be enterprise servers or networking devices

  • Dynamic NAT –an inside address is translated to an address from a pool of addresses

  • PAT (One-to-Many NAT, Overloading) –many inside addresses are translated to the same outside address. Different conversations are identified by port numbers

Network address translation nat3
Network Address Translation (NAT)

  • NAT provides a level of security for your inside network from the outside world

Nat terminology
NAT Terminology

  • Inside local IP address: The IP address assigned to a host on the inside network. The address is typically an RFC 1918 address.

  • Inside global IP address: A globally unique IP address (typically assigned by an ISP) that represents one or more inside local IP addresses to the outside world.

  • Outside global IP address: The IP address assigned to a host on the outside network by its owner. The address is globally unique.

Static ip address assignment
Static IP Address Assignment

  • An IP address is manually assigned to a device or host

  • The network administrator configures the IP address, default gateway, and name servers manually by entering them into a special file or files on the end system with either a graphical or text interface

  • Static address assignment is an extra burden for the administrator—especially on large-scale networks—who must configure the address on every end system in the network

  • Typically, routers, switches, servers, and printers have IP addresses statically assigned

Dynamic ip address assignment
Dynamic IP Address Assignment

  • IP addresses are automatically assigned to the devices

  • Dynamic address assignment relieves the administrator of manually assigning an address to every network device

  • Instead, the administrator must set up a server to assign the addresses.

  • On that server, the administrator defines the address pools and additional parameters that should be sent to the host (default gateway, name servers, time servers, and so forth)

  • On the host, the administrator enables the host to acquire the address dynamically; this is often the default.

  • When IP address reconfiguration is needed, the administrator reconfigures the server, which then performs the host-renumbering task

  • DHCP is the protocol used

Dynamic host configuration protocol dhcp
Dynamic Host Configuration Protocol (DHCP)

Is a protocol for assigning dynamic IP addresses to devices on a network . With dynamic addressing, a device can have a different IP address every time it connects to the network.

In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.

Dynamic host configuration protocol dhcp1
Dynamic Host Configuration Protocol (DHCP)

A DHCP Server can provide the following to a client:

IP address

Gateway address

Subnet mask

DNS server address


Domain Name

Domain Name Server(s)

Windows Server(s)

Classless interdomain routing cidr
Classless Interdomain Routing (CIDR)

What is CIDR?

CIDR is a new addressing scheme for the Internet which allows for more efficient allocation of IP addresses than the old Class A, B, and C address scheme.

Why Do We Need CIDR?

With a new network being connected to the Internet every 30 minutes the Internet was faced with two critical problems:

Running out of IP addresses

Running out of capacity in the global routing tables

Classless interdomain routing cidr1
Classless Interdomain Routing (CIDR)

Running Out of IP Addresses There is a maximum number of networks and hosts that can be assigned unique addresses using the Internet's 32-bit long addresses.

Traditionally, the Internet assigned "classes" of addresses: Class A, Class B and Class C were the most common. Each address had two parts: one part to identify a unique network and the second part to identify a unique host in that network.

Another way the old Class A, B, and C addresses were identified was by looking at the first 8 bits of the address and converting it to its decimal equivalent.

Classless interdomain routing cidr2
Classless Interdomain Routing (CIDR)

CIDR is pronounced “cider”

With CIDR, addresses use bit identifiers, or bit masks, instead of an address class to determine the network portion of an address

CIDR uses the /N notation instead of subnet masks

CIDR allows for the more efficient allocation of IP addresses

Classless interdomain routing cidr3
Classless Interdomain Routing (CIDR) /16 /24

Note that /22 is not a Class C network, it has a subnet mask of

Classless interdomain routing cidr4
Classless Interdomain Routing (CIDR)

CIDR Block Prefix Equivalent Class C of Host Addresses

/24 1 Class C 256 hosts

/23 2 Class C 512 hosts

/22 4 Class C 1,024 hosts

/21 8 Class C 2,048 hosts

/20 16 Class C 4,096 hosts/19 32 Class C 8,192 hosts

/18 64 Class C 16,384 hosts/17 128 Class C 32,768 hosts/16 256 Class C 65,536 hosts

Cidr and route aggregation
CIDR and Route Aggregation

  • CIDR allows routers to summarize, or aggregate, routing information

  • One address with a mask can represent multiple networks

  • This reduces the size of routing tables

  • Supernetting is another term for route aggregation

Cidr and route aggregation1
CIDR and Route Aggregation

Given four Class C Networks (/24): 11000000 10101000 00010000 00000000 11000000 10101000 0001000100000000 11000000 10101000 0001001000000000 11000000 10101000 0001001100000000

Identify which bits all these networks have in common. /22 can represent all these networks. The router will look at the first 22 bits of the address to make a routing decision. Note that /22 is not a Class C network, it has a subnet mask of

Importance of hierarchical addressing

Importance of Hierarchical Addressing

Without summarization, every small change in the network will be propagated (spread) throughout the entire network

Importance of hierarchical addressing1
Importance of Hierarchical Addressing

With summarization, small changes in the network aren’t propagated (spread) throughout the entire network

Subnet masks
Subnet Masks

  • A major network is a Class A, B, or C network

  • Fixed-Length Subnet Masking (FLSM) is when all subnet masks in a major network must be the same

  • Variable-Length Subnet Masking (VLSM) is when subnet masks within a major network can be different.

  • Some routing protocols require FLSM; others allow VLSM


  • VLSM makes it possible to subnet with different subnet masks and therefore results in more efficient address space allocation.

  • VLSM also provides a greater capability to perform route summarization, because it allows more hierarchical levels within an addressing plan.

  • VLSM requires prefix length information to be explicitly sent with each address advertised in a routing update

Classful and classless routing protocols
Classful and Classless Routing Protocols

  • Classful routing protocols DO NOT send subnet mask information in their routing updates

  • When a router receives a routing update, it simply assumes the default subnet mask (Class A, B, or C)

  • VLSM cannot be used in networks that use Classfulrouting protocols

  • Classless routing protocols send the subnet mask (prefix length) in their updates

  • VLSM can be used with Classless routing protocols

Classful versus classless1
Classful Versus Classless

  • When subnet masks aren’t sent in updates, routing problems can occur

  • Subnet masks should be sent in updates, otherwise routing problems can occur. The two 172.16.x.x /24 networks are separated by another network making the two networks discontinuous

  • The network is not hierarchical and appears to be a poor network design.

Classful and classless routing protocols1
Classful and Classless Routing Protocols

Classful protocols use address classes (A,B,C) to determine networks because subnet masks are not sent in routing updates.

Dns components
DNS Components

  • Resolver – The DNS client that sends queries to a Name Server

  • Name Servers –The DNS component that responds to queries and has the name to IP address mappings

  • Domain Name Space –The hierarchical system of names used on the Internet

    There is static and dynamic (DNS) name resolution.

Domain name space
Domain Name Space

Root Level Domain


Top Level Domain and Countries

(Australia com edu gov net org )

Second Level Domain

( microsoft franklin cisco )

(Seattle student)

Ipv6 standard
IPv6 Standard

  • Larger address space: IPv6 addresses are 128 bits, compared to IPv4’s 32 bits. This larger addressing space allows more support for addressing hierarchy levels, a much greater number of addressable nodes, and simpler auto configuration of addresses.

  • Globally unique IP addresses: Every node can have a unique global IPv6 address, which eliminates the need for NAT.

  • Site multi-homing: IPv6 allows hosts to have multiple IPv6 addresses and allows networks to have multiple IPv6 prefixes. Consequently, sites can have connections to multiple ISPs without breaking the global routing table.

  • Header format efficiency: A simplified header with a fixed header size makes processing more efficient.

Ipv6 standard1
IPv6 Standard

  • 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 non default quality of service (QoS) or real-time service.

Ipv6 standard2
IPv6 Standard

  • 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.

  • Improved global reach ability and flexibility.

  • Better aggregation of IP prefixes announced in routing tables.

Ipv6 standard3
IPv6 Standard

  • Multi-homed hosts. Multi-homing is a technique to increase the reliability of the Internet connection of an IP network. With IPv6, a host can have multiple IP addresses over one physical upstream link. For example, a host can connect to several ISPs.

  • Auto-configuration that can include Data Link layer addresses in the address space.

  • More plug-and-play options for more devices.

  • Public-to-private, end-to-end readdressing without address translation. This makes peer-to-peer (P2P) networking more functional and easier to deploy.

  • Simplified mechanisms for address renumbering and modification.

Ipv6 standard4
IPv6 Standard

  • Better routing efficiency for performance and forwarding-rate scalability

  • No broadcasts and thus no potential threat of broadcast storms

  • No requirement for processing checksums

  • Simplified and more efficient extension header mechanisms

  • Flow labels for per-flow processing with no need to open the transport inner packet to identify the various traffic flows

Ipv6 standard6
IPv6 Standard

Movement to change from IPv4 to IPv6 has already begun, particularly in Europe, Japan, and the Asia-Pacific region.

  • These areas are exhausting their allotted IPv4 addresses, which makes IPv6 all the more attractive and necessary.

  • In 2002, the European Community IPv6 Task Force forged a strategic alliance to foster IPv6 adoption worldwide.

  • The North American IPv6 Task Force has set out to engage the North American markets to adopt IPv6.

  • The first significant North American advances are coming from the U.S. Department of Defense (DoD).

Ipv6 address representation
IPv6 Address Representation

You know the 32-bit IPv4 address as a series of four 8-bit fields, separated by dots. However, larger 128-bit IPv6 addresses need a different representation because of their size. IPv6 addresses use colons to separate entries in a series of 16-bit hexadecimal

Ipv6 standard8
IPv6 Standard

  • Using the "::" notation greatly reduces the size of most addresses as shown. An address parser identifies the number of missing zeros by separating any two parts of an address and entering 0s until the 128 bits are complete

Ipv6 larger address space
IPv6 Larger Address Space


Global reach ability and flexibility



Auto configuration


End to end without NAT


Ipv6 standard10
IPv6 Standard

Simpler header

Routing efficiency

Performance and forwarding rate scalability

No broadcasts

No checksums

Extension headers

Flow labels

Ipv6 standard11
IPv6 Standard

Mobility and security

Mobile IP RFC-compliant

IPSec mandatory(or native) for IPv6

Transition richness

Dual stack

6to4 tunnels


Ipv6 larger address space1
IPv6 Larger address Space


32 bits or 4 bytes long

4,200,000,000 possible addressable nodes


128 bits or 16 bytes: four times the bits of IPv4

3.4 * 1038possible addressable nodes


5 * 1028addresses per person

Ipv6 larger address space3
IPv6 Larger Address space

Aggregation of prefixes announced in the global routing table

Efficient and scalable routing

Improved bandwidth and functionality for user traffic

Ipv6 simpler and efficient header
IPv6 Simpler and Efficient Header

A simpler and more efficient header means:

64-bit aligned fields and fewer fields

Hardware-based, efficient processing

Improved routing efficiency and performance

faster forwarding rate with better scalability

Ipv6 representation
IPv6 Representation

x:x:x:x:x:x:x:x,where x is a 16-bit hexadecimal field

Leading zeros in a field are optional:


Successive fields of 0 can be represented as ::, but only once per address.




FF01:0:0:0:0:0:0:1 >>> FF01::1

0:0:0:0:0:0:0:1 >>> ::1

0:0:0:0:0:0:0:0 >>> ::

Ipv6 addressing model
IPv6 Addressing Model

Addresses are assigned to interfaces

Change from IPv4 mode:

Interface “expected” to have multiple addresses

Addresses have scope

Link Local

Unique Local


Addresses have lifetime

Valid and preferred lifetime

Ipv6 address types
IPv6 Address Types


Address is for a single interface.

IPv6 has several types (for example, global and IPv4 mapped).



Enables more efficient use of the network

Uses a larger address range


One-to-nearest(allocated from unicast address space).

Multiple devices share the same address.

All anycast nodes should provide uniform service.

Source devices send packets to anycast address.

Routers decide on closest device to reach that destination.

Suitable for load balancing and content delivery services.

Ipv6 global unicast addresses
IPv6 Global Unicast Addresses

  • The global unicast and the anycast share the same address format.

  • Uses a global routing prefix—a structure that enables aggregation upward, eventually to the ISP.

  • A single interface may be assigned multiple addresses of any type (unicast, anycast, multicast).

  • Every IPv6-enabled interface must contain at least one loopback (::1/128)and one link-local address.

  • Optionally, every interface can have multiple unique local and global addresses.

  • Anycast address is a global unicast address assigned to a set of interfaces (typically on different nodes).

  • IPv6 anycast is used for a network multihomed to several ISPs that have multiple connections to each other.

Ipv6global unicast addresses
IPv6Global Unicast Addresses

Global unicast and anycast addresses are defined by a global routing prefix, a subnet ID, and an interface ID.

Ipv6 interface id
IPv6 Interface ID

  • Cisco uses the extended universal identifier (EUI)-64 format to do stateless autoconfiguration.

  • This format expands the 48-bit MAC address to 64 bits by inserting “FFFE” into the middle 16 bits.

  • To make sure that the chosen address is from a unique Ethernet MAC address, the universal/local (U/L bit) is set to 1 for global scope (0 for local scope).

Ipv6 standard12
IPv6 Standard

Cisco uses the extended universal identifier (EUI)-64 format to do stateless autoconfiguration.

This format expands the 48-bit MAC address to 64 bits by inserting “FFFE” into the middle 16 bits

Ipv6 unicast addressing
IPv6 Unicast Addressing

IPv6 addressing rules are covered by multiple RFCs.

Architecture defined by RFC 4291.

Unicast: One to one


Link local (FE80::/10)

A single interface may be assigned multiple IPv6 addresses of any type: unicast, anycast, or multicast.

Ipv6 multicasting
IPv6 Multicasting

Multicast is frequently used in IPv6 and replaces broadcast

Ipv6 standard13
IPv6 Standard

An IPv6 anycast address is a global unicast address that is assigned to more than one interface.

Ipv6 static assignment
IPv6 Static Assignment

  • Similar to IPv4

  • Administrator assigns address to each device

  • Static assignment using a manual interface ID

  • Static assignment using an EUI-64 interface ID

Ipv6 dynamic address assignment
IPv6 Dynamic Address Assignment

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 auto configuration: A router on the link advertises—either periodically or at the host’s request—network information, such as the 64-bit prefix of the local network and its willingness to function as a default router for the link.

Ipv6 standard14
IPv6 Standard

Mandatory address for communication between two IPv6 devices (similar to ARP but at Layer 3)

Automatically assigned by router as soon as IPv6 is enabled

Also used for next-hop calculation in routing protocols

Only link specific scope

Remaining 54 bits could be zero or any manual configured value

Remaining 54 bits

Ipv6 stateless autoconfiguration
IPv6 Stateless Autoconfiguration

  • A router sends network information to all the nodes on the local link.

  • A host can auto configure itself by appending its IPv6 interface identifier (64-bit format) to the local link prefix (64 bits).

  • The result is a full 128-bit address that is usable and guaranteed to be globally unique.

Ipv6 standard stateless autoconfiguration
IPv6 Standard Stateless Autoconfiguration

Stage 1: The PC sends a router solicitation to request a prefix for stateless auto configuration

Stage 2: The router replies with a router advertisement.

Ipv6 standard15
IPv6 Standard

  • 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 global unicast addressing
IPv6 Global Unicast Addressing

  • IPv6 has an address format that enables aggregation upward eventually to the ISP. Global unicast addresses typically consists of a 48-bit global routing prefix and a 16-bit subnet ID. Individual organizations can use a 16-bit subnet field to create their own local addressing hierarchy. This field allows an organization to use up to 65,535 individual subnets

Ipv6 transition strategies
IPv6 Transition Strategies

  • The transition from IPv4 does not require upgrades on all nodes at the same time. Many transition mechanisms enable smooth integration of IPv4 and IPv6. Other mechanisms that allow IPv4 nodes to communicate with IPv6 nodes are available. Different situations demand different strategies. The figure illustrates the richness of available transition strategies.

  • Recall the advice: "Dual stack where you can, tunnel where you must." These two methods are the most common techniques to transition from IPv4 to IPv6.

Ipv6 transition strategies1
IPv6 Transition Strategies

Dual stacking is an integration method in which a node has implementation and connectivity to both an IPv4 and IPv6 network. This is the recommended option and involves running IPv4 and IPv6 at the same time. Router and switches are configured to support both protocols, with IPv6 being the preferred protocol.

Ipv6 transition strategies2
IPv6 Transition Strategies

  • Tunneling

    The second major transition technique is tunneling. There are several tunneling techniques available, including:

    Manual IPv6-over-IPv4 tunneling -An IPv6 packet is encapsulated within the IPv4 protocol. This method requires dual-stack routers.

    Dynamic 6to4 tunneling -Automatically establishes the connection of IPv6 islands through an IPv4 network, typically the Internet. It dynamically applies a valid, unique IPv6 prefix to each IPv6 island, which enables the fast deployment of IPv6 in a corporate network without address retrieval from the ISPs or registries

Upcoming deadlines
Upcoming Deadlines

  • Assignement 8-2, Concept Questions 6 due June20.

  • Assignment 1-4-2 Network Design ProjectPhase 2: WAN Network Design due June 20

  • Assignement 10-1 Concept Questions 7 due July 4