Chap 7

1
Chap 7 Implementing IP Addressing Services
Learning Objectives

• Configure DHCP in an enterprise branch network
• Configure NAT on a Cisco router
• Configure new generation RIP (RIPng) to use IPv6

2
Dynamic Host Configuration Protocol (DHCP)

• Automatically assigns IP addresses
• Only DHCP server needs to be assigned an address
• Client computers are configured to accept address
  from server after boot-up

3
Dynamic Host Configuration Protocol

• Dynamic Host Configuration Protocol (DHCP) works
  in a client/server mode.
• DHCP enables DHCP clients on an IP network to
  obtain their configurations from a DHCP server.
• Less work is involved in managing an IP network
  when DHCP is used.
• The most significant configuration option the
  client receives from the server is its IP
  address.
• The DHCP protocol is described in RFC 2131

4
Dynamic Host Configuration Protocol

• There are three mechanisms used to assign an IP
  address to the client
• Automatic allocation DHCP assigns a permanent
  IP address to a client.
• Manual allocation The IP address for the client
  is assigned by the administrator. DHCP conveys
  the address to the client.
• Dynamic allocation DHCP assigns, or leases, an
  IP address to the client for a limited period of
  time.

5
Major DHCP features
6
Dynamic Host Configuration Protocol(DHCP)
DHCP Server
1. Discover (Broadcast)
PC 1
DHCP Pool
192.168.1.3 192.168.1.4 192.168.1.5 192.168.1.6
2. Offer (Unicast do you want 192.168.1.3?)
3. Request (Broadcast yes please)
4. Acknowledge (Unicast you have 192.168.1.3)
7
DHCP Detailed Operation

• Discover (Broadcast)
• Offer (Unicast)
• Request (Broadcast)
• Acknowledge (Unicast)

8
DHCP Message Format
16
31
8
0
24
OP Code
Hardware
HW Address
Hops
Transaction Identifier
Flags
Seconds
Client IP Address (CIADDR)
Your Address (YIADDR)
Server IP Address (SIADDR)
Gateway IP Address (GIADDR)
Client Hardware Address (CHADDR)
Server Name (SNAME)
Boot Filename
DHCP Options
9
DHCP Discover
Client broadcasts DHCP request on UDP port 67
10
DHCP Offer
Server responds to DHCP request on UDP port 68
11
Configure DHCP Server Exclude Addresses

• 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.

12
Configure DHCP Server DHCP Address Pool

• Configuring a DHCP server involves defining a
  pool of addresses to assign.
• The ip dhcp pool command creates a pool with the
  specified name and puts the router in DHCP
  configuration mode, which is identified by the
  Router(dhcp-config) prompt.

13
Configure DHCP Server DHCP Tasks

• Configure the available addresses and specify the
  subnet network number and mask of the DHCP
  address pool. Use the network statement to define
  the range of available addresses.
• Define the default gateway or router for the
  clients to use with the default-router command.

14
Configuring DHCP Server

• The DHCP service is enabled by default on
  versions of Cisco IOS that support it.
• To disable the service, use the no service dhcp
  command.
• Use the service dhcp global configuration command
  to re-enable the DHCP server process.

15
Verifying and Troubleshooting DHCP

• 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.

16
Verifying and Troubleshooting DHCP

• 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.

17
Verifying and Troubleshooting DHCP

• View multiple DHCP pools using the show ip dhcp
  pool command.

18
Verifying and Troubleshooting DHCP
From the Client PC command line, enter ltIPCONFIG
/ALLgt to display the IP settings of the computer
19
Configuring DHCP Client
DHCP Server
Fa0/0
Fa0/1
10.0.0.2
SOHO
ISP
10.0.0.3

• Cisco routers in SOHO and branch sites may have
  to be configured to accept an interface IP
  address from the ISPs DHCP server.
• Frequently, it is the Ethernet interface that is
  used to connect to a cable modem.

20
DHCP Relay

• DHCP clients use IP broadcasts to find the DHCP
  server on the
• segment - Routers do not forward these
  broadcasts.
• When possible, administrators should use the ip
  helper-address
• command to relay broadcast requests for these key
  UDP services.

21
DHCP Relay

• By default, the ip helper-address command
  forwards the following eight UDP services
• Time
• TACACS
• DNS
• BOOTP/DHCP Server
• BOOTP/DHCP Client
• TFTP
• NetBIOS Name Service
• NetBIOS datagram Service

22
Configuring IP helper addresses

• To configure RTA e0, the interface that receives
  the Host A
• broadcasts, to relay DHCP broadcasts as a unicast
  to the DHCP server,
• use the following commands
• RTA(config)interface e0
• RTA(config-if)ip helper-address 172.24.1.9

23
Trouble Shooting DHCP

• Resolving IP Address Conflicts
• Verify Physical Connectivity
• Test Network Connectivity by Configuring Client
  workstation with a Static IP Address
• Verify Switch Port Configuration (STP Portfast
  and other Commands)
• Distinguishing whether DHCP Clients Obtain IP
  address on the Same Subnet or VLAN as DHCP Server

24
Private Public IP Addresses

• Public Internet addresses are regulated by five
  Regional Internet Registries (RIRs)
• ARIN
• RIPE
• APNIC
• LACNIC
• AfriNIC

• All public Internet addresses must be registered
  with a Regional Internet Regiestry (RIR).
• Organisations can lease public addresses from an
  ISP.
• Only the registered holder of a public Internet
  address can assign that address to a network
  device.

25
Private IP Addresses
Class A

• 10.0.0.0 to 10.255.255.255

Class B

• 172.16.0.0 to 172.31.255.255

Class C

• 192.168.0.0 to 192.168.255.255

26
Network Address Translation
Router is configured to hide private IP
addresses by substituting them for the public IP
address assigned to its Internet interface, and
carrying out the reverse process for received
packets.
Source
Destination
Segment
201.134.56.3
80.51.23.1
192.168.1.100
192.168.1.1
80.51.23.1
192.168.1.101
Router
Destination
Source
Segment
192.168.1.101
201.134.56.3
Packet
27
Introducing NAT and PAT

• NAT, as defined by RFC 1631, is the process of
  swapping one address for another in the IP packet
  header.
• In practice, NAT is used to allow hosts that are
  privately addressed to access the Internet.
• NAT translations can occur dynamically or
  statically.
• The most powerful feature of NAT routers is their
  capability to use port address translation (PAT),
  which allows multiple inside addresses to map to
  the same outside address.

28
NAT Terms

• Cisco defines the following NAT terms
• Inside local address The IP address assigned to
  a host on the inside network. The address is
  usually not an IP address assigned by the
  Internet Network Information Centre (InterNIC) or
  service provider. This address is likely to be an
  RFC 1918 private address.
• Inside global address A legitimate IP address
  assigned by the InterNIC or service provider that
  represents one or more inside local IP addresses
  to the outside world.
• Outside global address The IP address assigned
  to a host on the outside network. The owner of
  the host assigns this address.

29
NAT Example
RTA
Outside Global
Inside Local
Inside Global
Outside Global

• The translation from Private source IP address
• to Public source IP address.

30
NAT Example
RTA
Inside Local
Outside Global
Outside Global
Inside Global

• Translation back, from Public destination IP
• address to Private destination IP address.

31
NAT Features

• Static NAT is designed to allow one-to-one
  mapping of local and global addresses. This is
  particularly useful for hosts which must have a
  consistent address that is accessible from the
  Internet. These internal hosts may be enterprise
  servers or networking devices.
• Dynamic NAT is designed to map a private IP
  address to a public address. Any IP address from
  a pool of public IP addresses is assigned to a
  network host.

32
NAT Overload

• NAT Overload allows you to use a single Public IP
  address and assign it up to 65,536 inside hosts
  (4,000 is more realistic).
• Modifies the TCP/UDP source port to track inside
  Host addresses if both hosts select the same
  source port.

33
NAT Benefits

• 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

34
NAT Drawbacks

• 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

35
Configuring Static NAT
Inside Network
Internet
S0/0/0 10.1.1.2
S0/1/0 209.165.200.255
Server 192.168.10.254
36
Configuring Dynamic NAT
S0/0/0 10.1.1.2
S0/1/0 209.165.200.255
192.168.10.10
Internet
192.168.11.11
37
Configuring NAT Overload (Single Address)
S0/0/0 10.1.1.2
S0/1/0 209.165.200.255
192.168.10.10
Internet
192.168.11.11
38
Configuring NAT Overload (Multiple Addresses)
S0/0/0 10.1.1.2
S0/1/0 209.165.200.255
192.168.10.10
Internet
192.168.11.11
39
Port Forwarding
WWW Server
S0/0/0 10.1.1.2
S0/1/0 209.165.200.255
192.168.10.10
Internet
Re-direct traffic for port 80 to 192.168.10.10
192.168.11.11

• 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.
• The problem is that NAT does not allow requests
  initiated from the outside. This situation can be
  resolved with manual intervention. Port
  forwarding allows the identification of specific
  ports that can be forwarded to inside hosts.

40
Verifying Troubleshooting NAT Configuration

• By default, NAT translation entries time out
  after 24 hours.
• It is sometimes useful to clear the dynamic
  entries sooner than the default timer. This is
  especially true when testing the NAT
  configuration.

41
Verifying Troubleshooting NAT Configuration
42
Verifying Troubleshooting NAT Configuration
43
Verifying Troubleshooting NAT Configuration
44
IPv6 The Reason Why
45
IPv4 / IPv6 Comparison

• There are so many IPv6 addresses available that
  many trillions of addresses could be assigned to
  every human being on the planet.
• There are approximately 665,570,793,348,866,943,89
  8,599 addresses per square meter of the surface
  of the planet Earth!

46
IPv6 Representation

• Mobility and security
• Mobile IP RFC-compliant
• IPsec mandatory (or native) for IPv6

• Enhanced IP addressing
• Global reachability and flexibility
• Aggregation
• Multihoming
• Autoconfiguration
• Plug-and-play
• End-to-end without NAT
• Renumbering

• Simple header
• Routing efficiency
• Performance and forwarding rate scalability
• No broadcasts
• No checksums
• Extension headers
• Flow labels

• Transition richness
• Dual-stack
• 6to4 and manual tunnels
• Translation

47
IPv6 Packet Header
16
31
24
8
0
4
Version
Flow Label
Traffic Class
Next Header
Hop Limit
Payload Length
Source IP Address
Source IP Address
Source IP Address
Source IP Address
Destination IP Address
Destination IP Address
Destination IP Address
Destination IP Address
48
IPv6 Addressing
20310000130F0000000009C0876A130B. An IPv6
address can be shortened by applying the
following guidelines

• Leading zeros in a field are optional. For
  example, the field 09C0 equals 9C0, and the field
  0000 equals 0. Therefore
• 20310000130F0000000009C0876A130B can be
  written as 20310130F000000009C0876A130B.
• Successive fields of zeros can be represented as
  two colons "". However, this shorthand method
  can only be used once in an address. Therefore
• 20310130F000000009C0876A130B can be
  written as 20310130F9C0876A130B.
• An unspecified address is written as "" because
  it contains only zeros.

49
IPv6 Address Examples

• FF010000001 becomes FF011
• 00000001 becomes 1
• 00000000 becomes
• FF010000000000000000000000001 becomes
  FF010000001 becomes FF011
• E3D700000000000051F400C8C0A86420 becomes
  E3D751F4C8C0A86420
• 3FFE050100080000026097FFFE40EFAB becomes
  3FFE5018026097FFFE40EFAB becomes
  3FFE501826097FFFE40EFAB

50
IPv6 Address Structure
128 Bits
Network Portion
Host Portion
48 Bits
16 Bits
64 Bits
Global Routing Prefix
Interface ID
Subnet ID

• Interface ID identifies a host interface
  address
• Subnet ID 65,536 possible subnets
• Global Routing Prefix issued by IANA or RIR to
  ISPs at /32 or /35 in length, ISPs then issue to
  customers with /48 mask

51
IPv6 Address Types
Address Type MSB (Binary) MSB (Hex)
Unspecified 00..0 /128
Loopback 00..1 1/128
Multicast 11111111 FF00/8
Link-Local Unicast 1111111010 FExx/10
Global Unicast 001 2xxx/4 Or 3xxx/4
52
Assigning IPv6 Addresses
64 Bits
Global Routing Prefix
Interface ID
Subnet ID

• IPv6 addresses use interface identifiers to
  identify interfaces on a link.
• 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).
• IPv6 address ID can be assigned statically or
  dynamically
• Static assignment using a manual interface ID
• Static assignment using an EUI-64 interface ID
• Stateless auto-configuration
• DHCP for IPv6 (DHCPv6)

53
Manual Interface ID Assignment

• Statically assign an IPv6 address to a device by
  manually assigning both the prefix (network) and
  interface ID (host) portion of the IPv6 address
• RouterX(config-if)ipv6 address
  2001DB82222727272/64

54
Manual Interface ID Assignment

• Each layer-2 MAC address consists of a 12-digit
  hexadecimal number, split into 2-digit pairs by
  colons 0757AC1FB276

• EUI-64 stretches IEEE 802 MAC addresses from 48
  to 64 bits by inserting 0xFFFE in the middle at
  the 24th bit of the MAC address to create a
  64-bit, unique interface identifier
• 0757ACFFFE1FB276

• Assign an EUI-64 address to the interface of a
  Cisco router
• RouterX(config-if)ipv6 address
  2001DB822227272/64 eui-64

55
IPv6 Transition Strategies

• Different transition mechanisms are available
• Dual stack
• Manual tunnel
• 6to4 tunnel
• ISATAP tunnel
• Teredo tunnel
• Different compatibility mechanisms
• Proxying and translation (NAT-PT)

"Dual stack where you can, tunnel where you
must."
56
Cisco Dual IOS Stack
IPv4 Internet
Fa0/1
IPv4
IPv6 Internet
Application
IPv6
Transport
IPv4
IPv6
Ethernet

• Cisco IOS Release 12.2(2)T and later are
  IPv6-ready. As soon as IPv4 and IPv6 is
  configured on the interface, it becomes
  dual-stacked and forwards IPv4 and IPv6 traffic
  on that interface.

57
IPv6 Tunnelling

• Tunneling is an integration method in which an
  IPv6 packet is encapsulated within another
  protocol, such as IPv4.
• Requires dual-stack routers

58
IPv6 Routing Considerations

• IPv6 address size - Address size affects the
  information-processing 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 each-four cycles to process
  source and destination address information
  reduction in performance.
• 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.

59
Routing Information Protocol Next Generation
(RIPng)

• RFC 2080 defines 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 includes the following features
• 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 FF029 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

60
Configure IPv6 Address
MAC Address 02603e47.1530
61
Configure RIPng With IPv6
R1 Config
R1
LAN1 2001db811/64
E0
R2 Config
R2
E1
LAN2 2001db812/64
62
Troubleshoot IPv6
63
Chap 7 Implementing IP Addressing Services
Learning Objectives

• Configure DHCP in an enterprise branch network
• Configure NAT on a Cisco router
• Configure new generation RIP (RIPng) to use IPv6

64
Any Questions?
65
Lab Topology
Chapter 7.1.8 Configuring DHCP
209.165.200.224/27
Fa0/0 192.168.20.1/24
S0/1/0
.225
S0/0/1 DCE
S0/0/0
DNS Server 192.168.20.254/24
.2
.1
www.cisco.com 209.165.201.30/27
10.2.2.0/30
10.1.1.0/30
S0/0/0 DCE
S0/0/1
.2
.1
WWW.publicsite.com 209.165.202.158/27
.1
Fa0/0
.1
Fa0/1
192.168.30.0/24
192.168.10.0/24
S3
S1
PC3
PC1
66
Chap 7.1.8 Configuring DHCP
67
Lab Topology
Chapter 7.2.8 Configuring NAT
209.165.200.224/27
Fa0/0 192.168.20.1/24
S0/1/0
S0/0/1 DCE
S0/0/0
Inside WWW Server Local 192.168.20.254/24 Global
209.165.202.131
.2
.1
Outside Host 209.165.201.14/28
10.2.2.0/30
10.1.1.0/30
S0/0/0 DCE
S0/0/1
.2
.1
WWW.publicsite.com 209.165.201.20/28
.1
Fa0/0
.1
Fa0/1
192.168.30.0/24
192.168.10.0/24
S3
S1
PC3 192.168.30.10
PC1 192.168.10.10
68
Chap 7.2.8 Configuring NAT
69
Lab Topology
Chapter 7.4.1 Configuring DHCP NAT
Fa0/0 192.168.20.1/24
S0/0/1 DCE
S0/0/0
Inside WWW Server Local 192.168.20.254/24 Global
209.165.200.246
.2
.225
209.165.200.224/30
10.1.1.0/30
S0/0/0 DCE
S0/0/1
.226
.1
Fa0/0
Fa0/1
192.168.10.0/24
.1
192.168.11.0/24
.1
S2
S1
PC2
PC1