CCNA EXPLORATION
ACCESSING THE WAN
Study Guide
Chapter 7: IP Addressing Services
7.1.1
What is DHCP?
7.1.2
Typically a network server is used to offer DHCP
services. What can be used in a SOHO location?
What are the three different address allocation
mechanisms DHCP uses when assigning IP
addresses?
Describe basic dynamic DHCP operation.
Describe the four steps in obtaining a lease
When the client boots or otherwise wants to
join a network.
CCNA EXP 4
DHCP assigns IP addresses and other important network
configuration information dynamically.
Cisco router can be configured to provide DHCP services.
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.
DHCP works in a client/server mode and operates like any
other client/server relationship. When a PC connects to a
DHCP server, the server assigns or leases an IP address to
that PC. The PC connects to the network with that leased IP
address until the lease expires. The host must contact the
DHCP server periodically to extend the lease. This lease
mechanism ensures that hosts that move or power off do not
hold onto addresses that they do not need. The DHCP server
returns these addresses to the address pool and reallocates
them as necessary.
Step 1. The client broadcasts a DHCPDISCOVER message. The
DHCPDISCOVER message finds DHCP servers on the network.
Because the host has no valid IP information at bootup, it
uses L2 and L3 broadcast addresses to communicate with the
server.
Step 2. When the DHCP server receives a DHCDISCOVER
message, it finds an available IP address to lease, creates an
ARP entry consisting of the MAC address of the requesting
host and the leased IP address, and transmits a binding offer
with a DHCPOFFER message. The DHCPOFFER message is
sent as a unicast, using the L2 MAC address of the server as
the source address and the L2 address of the client as the
destination.
Step 3. When the client receives the DHCPOFFER from the
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7.1.3
Describe BOOTP.
How are BOOTP & DHCP alike?
What are the three primary differences
between DHCP and BOOTP?
How are the message formats different
between BOOTP & DHCP?
Describe the DHCP message format.
How is the DHCPDISCOVER sent?
CCNA EXP 4
server, it sends back a DHCPREQUEST message. This message
has two purposes: lease origination and lease renewal and
verification. When used for lease origination, the
DHCPREQUEST of the client is requesting that the IP
information be verified just after it has been assigned. The
message provides error checking to ensure that the
assignment is still valid. The DHCPREQUEST also serves as a
binding acceptance notice to the selected server and an
implicit decline to any other servers that may have provided
the host a binding offer.
Step 4. On receiving the DHCPREQUEST message, the server
verifies the lease information, creates a new ARP entry for
the client lease, and replies with a unicast DHCPACK
message. The DHCPACK message is a duplicate of the
DHCPOFFER, except for a change in the message type field.
When the client receives the DHCPACK message, it logs the
configuration information and performs an ARP lookup for
the assigned address. If it does not receive a reply, it knows
that the IP address is valid and starts using it as its own.
The Bootstrap Protocol (BOOTP), defined in RFC 951, is the
predecessor of DHCP. It 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.
Both have a DHCP server & a client.
 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. BOOTP does
not use leases. Its clients have reserved IP address
which cannot be assigned to any other host.
 BOOTP provides a limited amount of information to a
host. DHCP provides additional IP configuration
parameters, such as WINS and domain name.
In DHCP the options field is added.
As an IP broadcast (destination IP address of
255.255.255.255).
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At this point what is the source address of the
client?
What other services can DHCP provide?
7.1.4
7.1.5
7.1.6
What are the steps to configure a router as a
DHCP server? Include router commands’ syntax.
What command disables DHCP?
What command displays a list of all IP address
to MAC address bindings that have been
provided by the DHCP service?
What command displays count information
regarding the number of DHCP messages that
have been sent and received?
What command is used to view multiple pools?
What command is used to configure an
Ethernet interface as a DHCP client?
To renew its IP address what command(s)
would be issued on a pc?
What is the Cisco IOS helper address?
How does the helper address apply in DHCP?
What command is needed to configure a router
as a DHCP relay agent?
By default what other UDP services does the
command in the answer above relay?
CCNA EXP 4
The client does not have a configured IP address, so the
source IP address of 0.0.0.0 is used.
The lease renewal time, domain name server, and NetBIOS
Name Service (Microsoft Windows Internet Name Service
[Microsoft WINS]).
Step 1. Define a range of addresses that DHCP is not to
allocate. These are usually static addresses reserved for the
router interface, switch management IP address, servers, and
local network printers.
R1(config)#ip dhcp excluded-address low address
{high address}
Step 2. Create the DHCP pool using the ip dhcp pool
command.
R1(config)#ip dhcp pool pool-name
Step 3. Configure the specifics of the pool.
Define the address pool
network network-number [mask | /prefix-length]
Define the default router or gateway
default-router address [address2...address8]
Define a DNS server.
dns-server address [address2...address8
Define the domain name
domain-name domain
Define the duration of the DHCP lease
lease {days [hours] [minutes] | infinite}
Define the NetBIOS WINS server
netbios-name-server address [address2...address8]
The no service dhcp command.
The show ip dhcp binding command.
The show ip dhcp server statistics command.
The show ip dhcp pool command.
The ip address dhcp command.
The ipconfig /release command then the ipconfig /renew
command.
Address configured on an interface to which broadcasts
received on that interface will be sent.
It 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.
The ip helper-address interface configuration command.
Port 37: Time
Port 49: TACACS
Port 53: DNS
Port 67: DHCP/BOOTP server
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7.1.7
7.1.8
To specify additional ports, what other
command is used?
What are the steps in configuring a DHCP server
using SDM?
What command displays all address conflicts
recorded by the DHCP server?
What command does the server use to detect
conflicts?
What does the client use to detect clients?
What command is used to confirm that the
router interface acting as the default gateway
for the client is operational?
If there is a switch between the client and the
DHCP server, what configuration changes
resolve the most common DHCP client issues
that occur with an initial installation of a
Catalyst switch.
How do you verify that the client is configured
to relay DHCP requests?
How do you verify that the router Is receiving
DHCP Requests?
7.2.1
7.2.2
All public Internet addresses must be registered
with what?
What is a private address?
What are the private internet addresses as
defined in RFC1918? Include their CIDR prefix.
Without a translation system, private hosts
behind a router in the network of one
organization cannot connect with private hosts
behind a router in other organizations over the
Internet. How is this overcome?
Describe the NATs basic operation.
CCNA EXP 4
Port 68: DHCP/BOOTP client
Port 69: TFTP
Port 137: NetBIOS name service
Port 138: NetBIOS datagram service
The ip forward-protocol command is used to specify exactly
which types of broadcast packets to forward.
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.
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.
Cisco SDM configures the router to automatically exclude the
LAN interface IP address in the pool
The show ip dhcp conflict command.
The ping command.
Address Resolution Protocol (ARP)
The show interface interface command.
Begin by verifying that the port has STP PortFast enabled and
trunking/channeling disabled. The default configuration is
PortFast disabled and trunking/channeling auto, if applicable.
Step 1. Verify that the ip helper-address command is
configured on the correct interface.
Step 2. Verify that the global configuration command no
service dhcp has not been configured.
By using the debug commands.
debug ip packet detail access-list number
debug ip dhcp server packet
dhcp server events
etc.
A Regional Internet Registry (RIR).
They are not to be routed over the Internet.
Class A: 10.0.0.0 - 10.255.255.255 10.0.0.0/8
Class B: 172.16.0.0 - 172.31.255.255 172.16.0.0/12
Class C: 192.168.0.0 - 192.168.255.255 192.168.0.0/16
Network Address Translation (NAT)
NAT-enabled routers retain one or many valid Internet IP
addresses outside of the network. When the client sends
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packets out of the network, NAT translates the internal IP
address of the client to an external address. To outside users,
all traffic coming to and going from the network has the
same IP address or is from the same pool of addresses.
Where does NAT typically operate?
At the border of a stub network. .A stub network is a
network that has a single connection to its neighbor network.
What is the inside network? Outside network?
The inside network is the set of networks that are subject to
translation. The outside network refers to all other
addresses.
Describe the four types of NAT addresses.
Inside local address - Usually not an IP address assigned by a
RIR or service provider and is most likely an RFC 1918 private
address.
Inside global address - Valid public address that the inside
host is given when it exits the NAT router.
Outside global address - Valid public IP address assigned to a
host on the Internet.
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.
Describe Dynamic NAT.
Uses a pool of public addresses and assigns them on a firstcome, 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.
Describe 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.
Describe NAT overloading.
It maps multiple private IP addresses to a single public IP
address or a few addresses.
What is another name for NAT overloading?
Port Address Translation or PAT
How does PAT track the mappings?
Multiple addresses can be mapped to one or to a few
addresses because each private address is also tracked by a
port number.
Describe this use of port numbers.
Port numbers are encoded in 16 bits. The total number of
internal addresses that can be translated to one external
address could theoretically be as high as 65,536 per IP
address. However, realistically, the number of internal
addresses that can be assigned a single IP address is around
4,000.
What happens if a source port is already used?
NAT overload attempts to preserve the original source port.
However, if this source port is already used, NAT overload
assigns the first available port number starting from the
beginning of the appropriate port group 0-511, 512-1023, or
1024-65535. When there are no more ports available and
there is more than one external IP address configured, NAT
overload moves to the next IP address to try to allocate the
original source port again. This process continues until it runs
out of available ports and external IP addresses.
CCNA EXP 4
CH.7 IP Addressing Services
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Compare & contrast NAT & PAT.
7.2.3
NAT generally only translates IP addresses on a 1:1
correspondence between publicly exposed IP addresses and
privately held IP addresses. PAT modifies both the private IP
address and port number of the sender. PAT chooses the port
numbers seen by hosts on the public network.
NAT routes incoming packets to their inside destination by
referring to the incoming source IP address given by the host
on the public network. With PAT, there is generally only one
or a very few publicly exposed IP addresses. Incoming
packets from the public network are routed to their
destinations on the private network by referring to a table in
the PAT device that tracks public and private port pairs. This
is called connection tracking.
 Conserves the legally registered addressing scheme
 Increases the flexibility of connections to the public
network
 Provides consistency for internal network addressing
schemes.
 Provides network security
 Performance is degraded
 End-to-end functionality is degraded
 End-to-end IP traceability is lost
 Tunneling is more complicated
 Initiating TCP connections can be disrupted
 Architectures need to be rebuilt to accommodate
changes
What are the advantages of NAT?
What are the disadvantages of NAT?
7.2.4
What are the steps to configuring Static NAT?
CCNA EXP 4
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7.2.5
What are the steps to configuring Dynamic
NAT?
7.2.6
What are the steps to configuring NAT Overload
for a Single Public IP Address?
CCNA EXP 4
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What are the steps to configuring NAT Overload
for a Pool of Public IP Addresses?
7.2.7
What is port forwarding?
Describe the operation of port forwarding.
7.2.8
What must you do Before using the show
commands to verify NAT?
What command displays the details of the NAT
assignments? How can you see additional
information about each translation?
What 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?
By default, when do translation entries timeout?
CCNA EXP 4
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.
Port forwarding allows users on the Internet to access
internal servers by using the WAN port address and the
matched external port number. When users send these types
of requests to your WAN port IP address via the Internet, the
router forwards those requests to the appropriate servers on
your LAN.
Clear any dynamic translation entries that might still be
present.
Use the clear ip nat translation global command.
The show ip nat translations command.
Adding verbose to the command displays additional
information about each translation.
The show ip nat statistics command.
After 24 hours.
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How can you change the time-out?
What command clears all translations from the
NAT table?
What are the steps to verify that NAT is
operating as expected?
7.3.1
What command is used to verify the operation
of the NAT feature by displaying information
about every packet that is translated by the
router?
What command generates a description of each
packet considered for translation and outputs
information about certain errors or exception
conditions, such as the failure to allocate a
global address?
Describe the IPv6 address.
What are some of the enhancements that IPv6
offers?
What is meant by multihomed hosts?
7.3.2
Describe the IPv6 Address Representation.
CCNA EXP 4
Use the ip nat translation timeout timeout_seconds
command in global configuration mode.
The clear ip nat translation * global command.
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.
The debug ip nat command.
The debug ip nat detailed command.
An IPv6 address is a 128-bit binary value, which can be
displayed as 32 hexadecimal digits.
Enhanced IP addressing
Global reachability and flexibility
Aggregation
Multihoming
Autoconfiguration
Plug-and-play
End-to-end without NAT
Renumbering
Simplified header
Routing efficiency
Performance and forwarding rate scalability
**No broadcasts**
No checksums
Extension headers
Flow labels
Mobility and security
Mobile IP RFC-compliant
IPsec mandatory (or native) for IPv6
Transition richness
Dual-stack
6to4 and manual tunnels
Translation
Hosts attached to multiple physical network segments in an
OSI CLNS network. A host can have multiple IP addresses over
one physical upstream link.
IPv6 addresses use colons to separate entries in a series of
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The text gives the example of
2031:0000:130F:0000:0000:09C0:876A:130B.
Describe how this address can be shortened.
What is a global unicast address?
Describe private IPv6 addresses.
Describe the two types of private IPv6
addresses.
What is the IPv6 loopback address?
CCNA EXP 4
16-bit hexadecimal.
 Leading zeros in a field are optional. For example, the
field 09C0 equals 9C0, and the field 0000 equals 0. So
2031:0000:130F:0000:0000:09C0:876A:130B can be
written as 2031:0:130F:0000:0000:9C0:876A:130B.
 Successive fields of zeros can be represented as two
colons "::". However, this shorthand method can only
be used once in an address. For example
2031:0:130F:0000:0000:9C0:876A:130B can be
written as 2031:0:130F::9C0:876A:130B.
 An unspecified address is written as "::" because it
contains only zeros.
An IPv6 unicast address that is globally unique. It can be
routed globally w/no modification. It shares the same
address format as an IPv6 anycast address. Are assigned by
IANA. It consists of a 48-bit global routing prefix and a 16-bit
subnet ID.
A block of IPv6 addresses is set aside for private addresses,
just as is done in IPv4. These private addresses are local only
to a particular link or site, and are therefore never routed
outside of a particular company network. Private addresses
have a first octet value of "FE" in hexadecimal notation, with
the next hexadecimal digit being a value from 8 to F.
Site-local addresses, are addresses similar to the RFC 1918
Address Allocation for Private Internets in IPv4 today. The
scope of these addresses is an entire site or organization.
However, the use of site-local addresses is problematic and is
being deprecated as of 2003 by RFC 3879. In hexadecimal,
site-local addresses begin with "FE" and then "C" to "F" for
the third hexadecimal digit.
Link-local addresses, are new to the concept of addressing
with IP in the Network layer. These addresses have a smaller
scope than site-local addresses; they refer only to a particular
physical link (physical network). Routers do not forward
datagrams using link-local addresses at all, not even within
the organization; they are only for local communication on a
particular physical network segment. They are used for link
communications such as automatic address configuration,
neighbor discovery, and router discovery. Many IPv6 routing
protocols also use link-local addresses. Link-local addresses
begin with "FE" and then have a value from "8" to "B" for the
third hexadecimal digit.
Just as in IPv4, a provision has been made for a special
loopback IPv6 address for testing; datagrams sent to this
address "loop back" to the sending device. However, in IPv6
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Describe the IPv6 Unspecified Address.
there is just one address, not a whole block, for this function.
The loopback address is 0:0:0:0:0:0:0:1, which is normally
expressed using zero compression as "::1".
In IPv4, an IP address of all zeroes has a special meaning; it
refers to the host itself, and is used when a device does not
know its own address. In IPv6, this concept has been
formalized, and the all-zeroes address (0:0:0:0:0:0:0:0) is
named the "unspecified" address. It is typically used in the
source field of a datagram that is sent by a device that seeks
to have its IP address configured. You can apply address
compression to this address; because the address is all
zeroes, the address becomes just "::".
Describe how additional hierarchy is added to
the 48-bit global routing prefix with the registry
prefix, ISP Prefix, and site prefix.
Describe the interface id.
Describe the four ways you can assign an IPv6
address ID statically or dynamically. Give
commands as needed.
CCNA EXP 4
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).
Manual Interface ID Assignment: manually assign both the
prefix (network) and interface ID (host) portion of the IPv6
address. To configure an IPv6 address on a Cisco router
interface, use the ipv6 address ipv6-address/prefix-length
command in interface configuration mode. Example:
RouterX(config-if)#ipv6 address 2001:DB8:2222:7272::72/64
EUI-64 Interface ID Assignment: to configure the prefix
(network) portion of the IPv6 address and derive the
interface ID (host) portion from the Layer 2 MAC address of
the device, which is known as the EUI-64 interface ID.
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. Example:
RouterX(config-if)#ipv6 address 2001:DB8:2222:7272::/64
eui-64
Stateless Autoconfiguration: automatically configures the
IPv6 address. In IPv6, it is assumed that non-PC devices, as
well as computer terminals, will be connected to the
network. The autoconfiguration mechanism was introduced
to enable plug-and-play networking of these devices to help
reduce administration overhead.
DHCPv6 (Stateful): enables DHCP servers to pass
configuration parameters, such as IPv6 network addresses, to
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Describe the EUI-64 interface.
7.3.3
Describe Dual Stacking.
Describe Tunneling.
Describe NAT-Protocol Translation (NAT-PT).
7.3.4
Describe the basic operation of dual stacking.
Describe API.
What command(s) enable the use of IPv6 on a
router?
CCNA EXP 4
IPv6 nodes. It offers the capability of automatic allocation of
reusable network addresses and additional configuration
flexibility. This protocol is a stateful counterpart to IPv6
stateless address autoconfiguration (RFC 2462), and can be
used separately or concurrently with IPv6 stateless address
autoconfiguration to obtain configuration parameters.
Extended Universal Identifier: an IPv6 address format
created by taking an interface’s MAC add.—48 bits in
length—and inserting another 16-bit hexadecimal string
(FFFE) between the OUI (1ST 24 bits) & unique serial number
(last 24 bits) of the MAC add. To ensure that the chosen add.
Is from a unique Ethernet MAC add., the 7th bit in the high
order byte is set to 1(equivalent to the IEEE G/L bit) to
indicate the uniqueness of the 48-bit address.
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.
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.
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.
Dual stacking is an integration method that allows a node to
have connectivity to an IPv4 and IPv6 network
simultaneously. Each node has two protocol stacks with the
configuration on the same interface or on multiple interfaces.
A dual-stack node chooses which stack to use based on the
destination address of the packet. A dual-stack node should
prefer IPv6 when it is available. Old IPv4-only applications
continue to work as before. New and modified applications
take advantage of both IP layers.
A new application programming interface (API) has been
defined to support IPv4 and IPv6 addresses and DNS
requests. An API facilitates the exchange of messages or data
between two or more different software applications.
Use the global configuration command ipv6 unicast-routing.
This command enables the forwarding of IPv6 datagrams.
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7.3.5
Describe IPv6 Tunneling.
What two issues arise from tunneling?
What considerations are a must for a manually
configured tunnel?
7.3.6
If IPv4 uses CIDR, what does IPv6 use?
What are the IPv6 routing control plane
considerations?
What are the IPv6 routing forwarding/data
plane considerations?
CCNA EXP 4
You must configure all interfaces that forward IPv6 traffic
with an IPv6 address using the ipv6 address IPv6-address
[/prefix length] interface command.
Tunneling is an integration method where an IPv6 packet is
encapsulated within another protocol, such as IPv4. This
method enables the connection of IPv6 islands without
needing to convert the intermediary networks to IPv6. When
IPv4 is used to encapsulate the IPv6 packet, a protocol type
of 41 is specified in the IPv4 header, and the packet includes
a 20-byte IPv4 header with no options and an IPv6 header
and payload. It also requires dual-stack routers.
The maximum transmission unit (MTU) is effectively
decreased by 20 octets if the IPv4 header does not contain
any optional fields. In addition, a tunneled network is often
difficult to troubleshoot.
The end routers must be dual stacked, and the configuration
cannot change dynamically as network and routing needs
change.
It uses longest prefix match routing.
IPv6 address size - Address size affects the informationprocessing functions of a router. Systems using a 64-bit CPU,
bus, or memory structure can pass both the IPv4 source and
destination address in a single processing cycle. For IPv6, the
source and destination addresses require two cycles eachfour cycles to process source and destination address
information. As a result, routers relying exclusively on
software processing are likely to perform slower than when
in an IPv4 environment.
Multiple IPv6 node addresses - Because IPv6 nodes can use
several IPv6 unicast addresses, memory consumption of the
Neighbor Discovery cache may be affected.
IPv6 routing protocols - IPv6 routing protocols are similar to
their IPv4 counterparts, but since an IPv6 prefix is four times
larger than an IPv4 prefix, routing updates have to carry
more information.
Routing table Size -Increased IPv6 address space leads to
larger networks and a much larger Internet. This implies
larger routing tables and higher memory requirements to
support them.
Parsing IPv6 extension headers - Applications, including
mobile IPv6, often use IPv6 address information in extension
headers, thus increasing their size. These additional fields
require additional processing. For example, a router using
ACLs to filter Layer 4 information needs to apply the ACLs to
packets with extension headers as well as those without. If
the length of the extension header exceeds the fixed length
of the hardware register of the router, hardware switching
fails, and packets may be punted to software switching or
dropped. This severely affects the forwarding performance of
the router.
IPv6 address lookup - IPv6 performs a lookup on packets
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How does the RIPNg Routing Protocol differ
using IPv6?
What is RIPng?
What are some of the features of RIPng?
7.3.7
In dual stack deployments which protocol is
used?
What are the two steps to activate IPv6 on a
router? List the appropriate commands.
entering the router to find the correct output interface. In
IPv4, the forwarding decision process parses a 32-bit
destination address. In IPv6, the forwarding decision could
conceivably require parsing a 128-bit address. Most routers
today perform lookups using an application-specific
integrated circuit (ASIC) with a fixed configuration that
performs the functions for which it was originally designed IPv4. Again, this could result in punting packets into slower
software processing, or dropping them all together.
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.
Routing Information Protocol next generation (RIPng) as a
simple routing protocol based on RIP. It provides a simple
way to bring up an IPv6 network without having to build a
new routing protocol.
It 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.
Based on IPv4 RIP version 2 (RIPv2) and is similar to RIPv2
Uses IPv6 for transport
Includes the IPv6 prefix and next-hop IPv6 address
Uses the multicast group FF02::9 as the destination address
for RIP updates (this is similar to the broadcast function
performed by RIP in IPv4)
Sends updates on UDP port 521
Is supported by Cisco IOS Release 12.2(2)T and later
Both RIP and RIPng are required.
Step1. Activate IPv6 traffic-forwarding on the router.
Use the global command ipv6 unicast-routing.
Step 2. Configure each interface that requires IPv6.
Use the ipv6 address interface command.
You can completely specify the IPv6 address or
compute the host identifier (rightmost 64 bits) from
the EUI-64 identifier of the interface.
What are two ways to perform name resolution
 Define a static name for an IPv6 address using the
from the Cisco IOS software process?
ipv6 host name [port] ipv6-address1 [ipv6address2...ipv6-address4] command. You can define
up to four IPv6 addresses for one hostname. The port
option refers to the Telnet port to be used for the
associated host.
 Specify the DNS server used by the router with the ip
name-server address command. The address can be
an IPv4 or IPv6 address. You can specify up to six DNS
servers with this command.
7.3.8 How do you configure RIPng with IPv6?
Before configuring the router to run IPv6 RIP, globally enable
IPv6 using the ipv6 unicast-routing global configuration
command, and enable IPv6 on any interfaces on which IPv6
CCNA EXP 4
CH.7 IP Addressing Services
APRIL 2009
RIP is to be enabled.
To enable RIPng routing on the router, use the ipv6 router rip
name global configuration command. The name parameter
identifies the RIP process. This process name is used later
when configuring RIPng on participating interfaces.
What is used instead of the network command
in RIPng?
7.3.9
Instead of using the network command to identify which
interfaces should run RIPng, you use the command ipv6 rip
name enable in interface configuration mode to enable RIPng
on an interface. The name parameter must match the name
parameter in the ipv6 router rip command.
What are some of the commands used to
troubleshoot RIPng problems?
CCNA EXP 4
CH.7 IP Addressing Services
APRIL 2009