Transcript The Internet and Its Uses

Implementing IP
Addressing Services
Accessing the WAN – Chapter 7
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Objectives

Configure DHCP in an enterprise branch network

Configure NAT on a Cisco router

Configure new generation RIP (RIPng) to use IPv6
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Introducing DHCP
Every device that connects to a network needs an IP address. Network
administrators assign static IP addresses to routers, servers, and other network
devices whose locations (physical and logical) are not likely to change.
Administrators enter static IP addresses manually when they configure devices to
join the network. Static addresses also enable administrators to manage those
devices remotely.
However, computers in an organization often change locations, physically and
logically. Administrators are unable to keep up with having to assign new IP
addresses every time an employee moves to a different office or cubicle. Desktop
clients do not require a static address. Instead, a workstation can use any address
within a range of addresses. This range is typically within an IP subnet
DHCP assigns IP addresses and other important network configuration information
dynamically. Because desktop clients typically make up the bulk of network nodes,
DHCP is an extremely useful and timesaving tool for network administrators. RFC
2131 describes DHCP.
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Introducing DHCP
Administrators typically prefer a network server to offer DHCP services, because
these solutions are scalable and relatively easy to manage. However, in a small
branch or SOHO location, a Cisco router can be configured to provide DHCP
services without the need for an expensive dedicated server. A Cisco IOS feature
set called Easy IP offers an optional, full-featured DHCP server.
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DHCP Operation
Providing IP addresses to clients is the most fundamental task performed by a
DHCP server. DHCP includes three different address allocation mechanisms to
provide flexibility when assigning IP addresses:
Manual Allocation: The administrator assigns a pre-allocated IP address to the client and
DHCP only communicates the IP address to the device.
Automatic Allocation: DHCP automatically assigns a static IP address permanently to
a device, selecting it from a pool of available addresses. There is no lease and the
address is permanently assigned to a device.
Dynamic Allocation: DHCP automatically dynamically assigns, or leases, an IP
address from a pool of addresses for a limited period of time chosen by the server, or
until the client tells the DHCP server that it no longer needs the address.
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BOOTP vs. DHCP
The Bootstrap Protocol (BOOTP), defined in RFC 951, is the
predecessor of DHCP and shares some operational
characteristics. BOOTP is a way to download address and boot
configurations for diskless workstations. A diskless workstation
does not have a hard drive or an operating system.
For example, many automated cash register systems at your local
supermarket are examples of diskless workstations
Both DHCP and BOOTP are client/server based and use UDP
ports 67 and 68. Those ports are still known as BOOTP ports.
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BOOTP vs. DHCP
There are three primary differences between DHCP
and BOOTP:
The main difference is that BOOTP was designed for manual pre-configuration of
the host information in a server database, while DHCP allows for dynamic allocation
of network addresses and configurations to newly attached hosts.
DHCP allows for recovery and reallocation of network addresses through a leasing
mechanism. Specifically, DHCP defines mechanisms through which clients can be
assigned an IP address for a finite lease period. This lease period allows for
reassignment of the IP address to another client later, or for the client to get
another assignment if the client moves to another subnet. Clients may also renew
leases and keep the same IP address. BOOTP does not use leases.
BOOTP provides a limited amount of information to a host. DHCP provides
additional IP configuration parameters, such as WINS and domain name
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DHCP Server Configuration
Cisco routers running Cisco IOS software provide full support for a router
to act as a DHCP server. The Cisco IOS DHCP server assigns and
manages IP addresses from specified address pools within the router to
DHCP clients.
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Verify DHCP Server Configuration
To verify the operation of DHCP, use the show ip dhcp binding command.
This command displays a list of all IP address to MAC address bindings that
have been provided by the DHCP service.
To verify that messages are being received or sent by the router, use the
show ip dhcp server statistics command. This command displays count
information regarding the number of DHCP messages that have been sent
and received.
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DHCP Client Configuration
 Typically, small broadband routers for home use, such as Linksys routers, can be
configured to connect to an ISP using a DSL or cable modem. In most cases, small
home routers are set to acquire an IP address automatically from their ISPs. For
example, the figure shows the default WAN setup page for a Linksys WRVS4400N
router. Notice that the Internet connection type is set to Automatic Configuration DHCP. This means that when the router is connected to a cable modem, for
example, it is a DHCP client and requests an IP address from the ISP.
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DHCP Client Configuration
Cisco routers in SOHO and branch sites have to be configured in a similar manner.
The method used depends on the ISP. However, in its simplest configuration, the
Ethernet interface is used to connect to a cable modem. To configure an Ethernet
interface as a DHCP client, the ip address dhcp command must be configured.
In the figure, assume that an ISP has been configured to provide select customers with IP
addresses from the 209.165.201.0 / 27 range. The ouput confirms the assigned address.
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DHCP Relay
In a complex hierarchical network, enterprise servers are usually contained in
a server farm. These servers may provide DHCP, DNS, TFTP, and FTP
services for the clients. The problem is that the network clients typically are
not on the same subnet as those servers. Therefore, the clients must locate
the servers to receive services and often these services are located using
broadcast messages.
In the figure, PC1 is attempting to acquire an IP address from the DHCP
server located at 192.168.11.5. In this scenario router R1 is not
configured as a DHCP server.
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DHCP Relay
A simpler solution is to configure the Cisco IOS helper address feature on
intervening routers and switches. This solution enables routers to forward DHCP
broadcasts to the DHCP servers. When a router forwards address
assignment/parameter requests, it is acting as a DHCP relay agent.
For example, PC1 would broadcast a request to locate a DHCP server. If router R1
were configured as a DHCP relay agent, it would intercept this request and forward
it to the DHCP server located on subnet 192.168.11.0.
To configure router R1 as a DHCP relay agent, you need to configure the nearest
interface to the client with the ip helper-address interface configuration command.
This command relays broadcast requests for key services to a configured address.
Configure the IP helper address on the interface receiving the broadcast.
Router R1 is now configured as a DHCP relay agent. It accepts broadcast requests
for the DHCP service and then forwards them as a unicast to the IP address
192.168.11.5.
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DHCP Configuration with SDM
Cisco routers can also be configured as a DHCP server using SDM.
In this example, router R1 will be configured as the DHCP server on
the Fa0/0 and Fa0/1interfaces.
The DHCP server function is enabled under Additional Tasks in the
Configure tab. From the list of tasks, click on the DHCP folder and then
select DHCP Pools to add a new pool. Click Add to create the new DHCP
pool.
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DHCP Configuration with SDM
The Add DHCP Pool window contains the options you need to configure
the DHCP IP address pool. The IP addresses that the DHCP server
assigns are drawn from a common pool. To configure the pool, specify the
starting and ending IP addresses of the range.
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DHCP Configuration with SDM
This screen provides you
with a summary of the pools
configured on your router. In
this example, there have
been two pools configured,
one for each of the Fast
Ethernet interfaces on the
R1 router.
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Troubleshooting DHCP
DHCP problems can arise for a multitude of reasons, such as software
defects in operating systems, NIC drivers, or DHCP/BOOTP relay agents,
but the most common are configuration issues. Because of the number of
potentially problematic areas, a systematic approach to troubleshooting is
required.
show ip dhcp conflict
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Verify DHCP Relay
Follow these steps to verify the router configuration:
Step 1. Verify that the ip helper-address command is configured on the correct
interface. It must be present on the inbound interface of the LAN containing the
DHCP client workstations and must be directed to the correct DHCP server. In the
figure, the output of the show running-config command verifies that the DHCP relay
IP address is referencing the DHCP server address at 192.168.11.5.
Step 2. Verify that the global configuration command no service dhcp has not been
configured. This command disables all DHCP server and relay functionality on the
router. The command service dhcp does not appear in the configuration, because it
is the default configuration.
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Private and Public Addressing
All public Internet addresses must be registered with a Regional Internet Regiestry (RIR).
Organizations can lease public addresses from an ISP. Only the registered holder of a
public Internet address can assign that address to a network device.
You may have noticed that all the examples in this course use a somewhat restricted
number of IP addresses. You may also have noticed the similarity between these numbers
and numbers you have used in a small network to view the setup web pages of many
brands of printers, DSL and cable routers, and other peripherals. These are reserved
private Internet addresses drawn from the three blocks shown in the figure. These
addresses are for private, internal network use only. Packets containing these addresses
are not routed over the Internet, and are referred to as non-routable addresses. RFC 1918
provides details.
Unlike public IP addresses, private IP addresses are a reserved block of numbers that can
be used by anyone. That means two networks, or two million networks, can each use the
same private addresses. To prevent addressing conflicts, routers must never route private
IP addresses. To protect the public Internet address structure, ISPs typically configure the
border routers to prevent privately addressed traffic from being forwarded over the Internet.
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What is NAT?
NAT has many uses, but its key use is to save IP addresses by
allowing networks to use private IP addresses. NAT translates nonroutable, private, internal addresses into routable, public addresses.
NAT has an added benefit of adding a degree of privacy and security
to a network because it hides internal IP addresses from outside
networks.
A NAT-enabled device typically operates at the border of a stub
network. In our example, R2 is the border router. A stub network is a
network that has a single connection to its neighbor network. As
seen from the ISP, R2 forms a stub network.
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What is NAT?
Inside local address - Usually not an IP address assigned by a RIR or service
provider and is most likely an RFC 1918 private address. In the figure, the IP
address 192.168.10.10 is assigned to the host PC1 on the inside network.
Inside global address - Valid public address that the inside host is given when it
exits the NAT router. When traffic from PC1 is destined for the web server at
209.165.201.1, router R2 must translate the address. In this case, IP address
209.165.200.226 is used as the inside global address for PC1.
Outside global address - Valid public IP address assigned to a host on the
Internet. For example, the web server is reachable at IP address 209.165.201.1.
Outside local address - The local IP address assigned to a host on the outside
network. In most situations, this address will be identical to the outside global
address of that outside device.
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What is NAT?
Dynamic Mapping and Static Mapping
There are two types of NAT translation: dynamic and
static.
Dynamic NAT uses a pool of public addresses and assigns
them on a first-come, first-served basis. When a host with a
private IP address requests access to the Internet, dynamic
NAT chooses an IP address from the pool that is not already
in use by another host. This is the mapping described so far.
Static NAT uses a one-to-one mapping of local and global
addresses, and these mappings remain constant. Static
NAT is particularly useful for web servers or hosts that must
have a consistent address that is accessible from the Internet.
These internal hosts may be enterprise servers or networking
devices.
Both static and dynamic NAT require that enough public
addresses are available to satisfy the total number of
simultaneous user sessions.
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What is NAT?
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 Internet.
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NAT advantages and disadvantages
NAT provides many benefits and advantages. However, there are
some drawbacks to using NAT, including the lack of support for
some types of traffic.
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Configure NAT on a Cisco Router
Configuring static NAT translations is a simple task. You need to define the
addresses to translate and then configure NAT on the appropriate
interfaces.Packets arriving on an inside interface from the identified IP address are
subject to translation. Packets arriving on an outside interface addressed to the
identified IP address are subject to translation
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Configure NAT on a Cisco Router
 While static NAT provides a permanent mapping between an internal
address and a specific public address, dynamic NAT maps private IP
addresses to public addresses. These public IP addresses come from a
NAT pool.
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Configure NAT on a Cisco Router
 There are two possible ways to configure overloading, depending on how
the ISP allocates public IP addresses. In the first instance, the ISP
allocates one public IP address to the organization, and in the other, it
allocates more than one public IP address.
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Describe how to configure port forwarding on a
Cisco Router
 Port forwarding
(sometimes referred to
as tunneling) is the act of
forwarding a network
port from one network
node to another. This
technique can allow an
external user to reach a
port on a private IP
address (inside a LAN)
from the outside through
a NAT-enabled router
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Verifying and Troubleshoot NAT Configurations
Verifying NAT and NAT Overload
It is important to verify NAT operation. There are several useful router commands to
view and clear NAT translations.
One of the most useful commands when verifying NAT operation is the show ip nat
translations command. Before using the show commands to verify NAT, you must
clear any dynamic translation entries that might still be present, because by default,
dynamic address translations time out from the NAT translation table after a period
of non-use.
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Verifying and Troubleshoot NAT Configurations
The show ip nat statistics command displays information about the total
number of active translations, NAT configuration parameters, how many
addresses are in the pool, and how many have been allocated.
In the figure, the hosts have initiated web traffic as well as ICMP traffic.
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Verifying and Troubleshoot NAT Configurations
Follow these steps to verify that NAT is operating as expected:
Step 1. Based on the configuration, clearly define what NAT is supposed
to achieve. This may reveal a problem with the configuration.
Step 2. Verify that correct translations exist in the translation table using
the show ip nat translations command.
Step 3. Use the clear and debug commands to verify that NAT is operating
as expected. Check to see if dynamic entries are recreated after they are
cleared.
Step 4. Review in detail what is happening to the packet, and verify that
routers have the correct routing information to move the packet.
Use the debug ip nat command to verify the operation of the NAT feature
by displaying information about every packet that is translated by the
router.
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Reasons for Using IPv6
To comprehend the IP addressing issues facing network administrators
today, consider that the IPv4 address space provides approximately
4,294,967,296 unique addresses. Of these, only 3.7 billion addresses are
assignable because the IPv4 addressing system separates the addresses into
classes and reserves addresses for multicasting, testing, and other specific
uses.
Based on figures as recent as January 2007, about 2.4 billion of the available
IPv4 addresses are already assigned to end users or ISPs. That leaves
roughly 1.3 billion addresses still available from the IPv4 address space.
Despite this seemingly large number, IPv4 address space is running out.
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Reasons for Using IPv6
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. Japan officially
started the move in 2000 when the Japanese government mandated the
incorporation of IPv6 and set a deadline of 2005 to upgrade existing systems in
every business and public sector. Korea, China, and Malaysia have launched
similar initiatives.
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).
Looking into the future and knowing the advantages of IP-enabled devices, DoD
mandated, as early as 2003, that all new equipment purchased not only be IPenabled, but also be IPv6-capable. In fact, all U.S. government agencies must start
using IPv6 across their core networks by 2008, and the agencies are working to
meet that deadline.
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Reasons for Using IPv6
Pv6 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.
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Reasons for Using IPv6
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.
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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.
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IPv6 Address Management
IPv6 addresses use interface identifiers to identify interfaces on a link.
Think of them as the host portion of an IPv6 address. Interface identifiers
are required to be unique on a specific link. Interface identifiers are always
64 bits and can be dynamically derived from a Layer 2 address (MAC).
You can assign an IPv6 address ID statically or dynamically:
Static assignment using a manual interface ID
Static assignment using an EUI-64 interface ID
Stateless autoconfiguration
DHCP for IPv6 (DHCPv6)
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IPv6 Address Management
To configure an IPv6 address on a Cisco router interface and enable
IPv6 processing using EUI-64 on that interface, use the ipv6 address
ipv6-prefix/prefix-length eui-64 command in interface configuration
mode.
ipv6 address IPv6-address [/prefix length] interface command.
RouterX(config-if)#ipv6 address 2001:DB8:2222:7272::/64 eui-64
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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.
Dual Stacking
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.
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
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IPv6 Transition Strategies
Other less popular tunneling techniques that are beyond the scope
of this course include:
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) tunneling Automatic overlay tunneling mechanism that uses the underlying IPv4
network as a link layer for IPv6. ISATAP tunnels allow individual IPv4 or
IPv6 dual-stack hosts within a site to communicate with other such hosts
on a virtual link, creating an IPv6 network using the IPv4 infrastructure.
Teredo tunneling - An IPv6 transition technology that provides host-to-host
automatic tunneling instead of gateway tunneling. This approach passes
unicast IPv6 traffic when dual-stacked hosts (hosts that are running both
IPv6 and IPv4) are located behind one or multiple IPv4 NATs.
NAT-Protocol Translation (NAT-PT)
Cisco IOS Release 12.3(2)T and later (with the appropriate feature set)
also include NAT-PT between IPv6 and IPv4. This translation allows direct
communication between hosts that use different versions of the IP
protocol. These translations are more complex than IPv4 NAT. At this
time, this translation technique is the least favorable option and should be
used as a last resort.
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IPv6 Dual Stacking
Dual Stacking
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.
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IPv6 Tunneling
The concept of IPv6 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.
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Configure New Generation RIP (RIPng) to
use IPv6
IPv6 routes use the same protocols and techniques as IPv4. Although the addresses are longer,
the protocols used in routing IPv6 are simply logical extensions of the protocols used in IPv4.
RFC 2080 defines Routing Information Protocol next generation (RIPng) as a simple routing
protocol based on RIP. RIPng is no more or less powerful than RIP, however, it provides a
simple way to bring up an IPv6 network without having to build a new routing protocol.
RIPng is a distance vector routing protocol with a limit of 15 hops that uses split horizon and
poison reverse updates to prevent routing loops. Its simplicity comes from the fact that it does
not require any global knowledge of the network. Only neighboring routers exchange local
messages.
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Configure New Generation RIP (RIPng) to
use IPv6
There are two basic steps to activate IPv6 on a router. First, you must activate IPv6
traffic-forwarding on the router, and then you must configure each interface that
requires IPv6.
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Configure New Generation RIP (RIPng) to
use IPv6
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Verify New Generation RIP (RIPng) to use
IPv6
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Summary
 Dynamic Host Control Protocol (DHCP)
This is a means of assigning IP address and other configuration
information automatically.
 DHCP operation
–3 different allocation methods
•Manual
•Automatic
•Dynamic
–Steps to configure DHCP
•Define range of addresses
•Create DHCP pool
•Configure DHCP pool specifics
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Summary
 DHCP Relay
Concept of using a router configured to listen for DHCP
messages from DHCP clients and then forwards those
messages to servers on different subnets
 Troubleshooting DHCP
–Most problems arise due to configuration errors
–Commands to aid troubleshooting
•Show ip dhcp
•Show run
•debug
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Summary
 Private IP addresses
–Class A = 10.x.x.x
–Class B = 172.16.x.x – 172.31.x.x
–Class C = 192.168.x.x
 Network Address Translation (NAT)
–A means of translating private IP addresses to public IP
addresses
–Type s of NAT
•Static
•Dynamic
–Some commands used for troubleshooting
•Show ip nat translations
•Show ip nat statistics
•Debug ip nat
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Summary
 IPv6
–A 128 bit address that uses colons to separate entries
–Normally written as 8 groups of 4 hexadecimal digits
 Cisco IOS Dual Stack
–A way of permitting a node to have connectivity to an IPv4 &
IP v6 network simultaneously
 IPv6 Tunneling
–An IPV6 packet is encapsulated within another protocol
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Summary
 Configuring RIPng with IPv6
1st globally enable IPv6
2nd enable IPv6 on interfaces on which IPv6 is to be enabled
3rd enable RIPng using either
ipv6 rotuer rip name
ipv6 router name enable
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