Ch.2 – Advanced IP Address Management

1
Ch.2 Advanced IP Address Management

• CCNP 1 version 3.0 Advanced Routing
• Rick Graziani
• Cabrillo College

2
Note to instructors

• If you have downloaded this presentation from the
  Cisco Networking Academy Community FTP Center,
  this may not be my latest version of this
  PowerPoint.
• For the latest PowerPoints for all my CCNA, CCNP,
  and Wireless classes, please go to my web site
• http//www.cabrillo.cc.ca.us/rgraziani/
• The username is cisco and the password is perlman
  for all of my materials.
• If you have any questions on any of my materials
  or the curriculum, please feel free to email me
  at graziani_at_cabrillo.edu (I really dont mind
  helping.) Also, if you run across any typos or
  errors in my presentations, please let me know.
• I will add (Updated date) next to each
  presentation on my web site that has been updated
  since these have been uploaded to the FTP center.
• Thanks! Rick

3
Objectives

• This module explores the evolution and extension
  of IPv4, including the key scalability features
  that engineers have added to it over the years
• Subnetting
• Classless interdomain routing (CIDR)
• Variable length subnet masking (VLSM)
• Route summarization
• Finally, this module examines advanced IP
  implementation techniques such as the following
• IP unnumbered
• Dynamic Host Configuration Protocol (DHCP)
• Helper addresses

4
A few notes

• The following slides are NOT from the online
  curriculum.
• However, they do cover the same topics, just with
  different examples.

5
IPv4 Address Classes
6
IPv4 Address Classes

• No medium size host networks
• In the early days of the Internet, IP addresses
  were allocated to organizations based on request
  rather than actual need.

7
IPv4 Address Classes

• Class D Addresses
• A Class D address begins with binary 1110 in the
  first octet.
• First octet range 224 to 239.
• Class D address can be used to represent a group
  of hosts called a host group, or multicast group.
• Class E AddressesFirst octet of an IP address
  begins with 1111
• Class E addresses are reserved for experimental
  purposes and should not be used for addressing
  hosts or multicast groups. 

8
IP addressing crisis

• Address Depletion
• Internet Routing Table Explosion

9
IPv4 Addressing

• Subnet Mask
• One solution to the IP address shortage was
  thought to be the subnet mask.
• Formalized in 1985 (RFC 950), the subnet mask
  breaks a single class A, B or C network in to
  smaller pieces.

10
Subnet Example
Given the Class B address 190.52.0.0
Class B
Network
Network
Host
Host

• Using /24 subnet...
• 190.52.1.2
• 190.52.2.2
• 190.52.3.2

Internet routers still see this net as
190.52.0.0
But internal routers think all these addresses
are on different networks, called subnetworks
11
Subnet Example

• Using the 3rd octet, 190.52.0.0 was divided into
• 190.52.1.0 190.52.2.0 190.52.3.0
  190.52.4.0
• 190.52.5.0 190.52.6.0 190.52.7.0
  190.52.8.0
• 190.52.9.0 190.52.10.0 190.52.11.0
  190.52.12.0
• 190.52.13.0 190.52.14.0 190.52.15.0
  190.52.16.0
• 190.52.17.0 190.52.18.0 190.52.19.0 and so on
  ...

12
All Zeros and All Ones Subnets

• Using the All Ones Subnet
• There is no command to enable or disable the use
  of the all-ones subnet, it is enabled by default.
• Router(config)ip subnet-zero
• The use of the all-ones subnet has always been
  explicitly allowed and the use of subnet zero is
  explicitly allowed since Cisco IOS version 12.0.
• RFC 1878 states, "This practice (of excluding
  all-zeros and all-ones subnets) is obsolete!
  Modern software will be able to utilize all
  definable networks." Today, the use of subnet
  zero and the all-ones subnet is generally
  accepted and most vendors support their use,
  though, on certain networks, particularly the
  ones using legacy software, the use of subnet
  zero and the all-ones subnet can lead to
  problems.
• CCO Subnet Zero and the All-Ones Subnet
  http//www.cisco.com/en/US/tech/tk648/tk361/techno
  logies_tech_note09186a0080093f18.shtml

13
Need a Subnet Review?

• If you need a Review of Subnets, please review
  the following links on my web site
• Subnet Review (PowerPoint)
• Subnets Explained (Word Doc)

14
Long Term Solution IPv6 (coming)

• IP v6, or IPng (IP the Next Generation) uses a
  128-bit address space, yielding
• 340,282,366,920,938,463,463,374,607,431,768,2
  11,456
• possible addresses.
• IPv6 has been slow to arrive
• IPv4 revitalized by new features, making IPv6 a
  luxury, and not a desperately needed fix
• IPv6 requires new software IT staffs must be
  retrained
• IPv6 will most likely coexist with IPv4 for years
  to come.
• Some experts believe IPv4 will remain for more
  than 10 years.

15
Short Term Solutions IPv4 Enhancements

• CIDR (Classless Inter-Domain Routing) RFCs
  1517, 1518, 1519, 1520
• VLSM (Variable Length Subnet Mask) RFC 1009
• Private Addressing - RFC 1918
• NAT/PAT (Network Address Translation / Port
  Address Translation) RFC

16
CIDR (Classless Inter-Domain Routing)

• By 1992, members of the IETF were having serious
  concerns about the exponential growth of the
  Internet and the scalability of Internet routing
  tables.
• The IETF was also concerned with the eventual
  exhaustion of 32-bit IPv4 address space.
• Projections were that this problem would reach
  its critical state by 1994 or 1995.
• IETFs response was the concept of Supernetting
  or CIDR, cider.
• To CIDR-compliant routers, address class is
  meaningless.
• The network portion of the address is determined
  by the network subnet mask, network-prefix or
  prefix-length (/8, /19, etc.)
• The network address is NOT determined by the
  first octet (first two bits), 200.10.0.0/16 or
  15.10.160.0/19
• CIDR helped reduced the Internet routing table
  explosion with supernetting and reallocation of
  IPv4 address space.

17
Active BGP entries
Report last updated at Thu, 16 Jan 2003

• http//bgp.potaroo.net/

18
CIDR (Classless Inter-Domain Routing)

• First deployed in 1994, CIDR dramatically
  improves IPv4s scalability and efficiency by
  providing the following
• Eliminates traditional Class A, B, C addresses
  allowing for more efficient allocation of IPv4
  address space.
• Supporting route aggregation (summarization),
  also known as supernetting, where thousands of
  routes could be represented by a single route in
  the routing table.
• Route aggregation also helps prevent route
  flapping on Internet routers using BGP. Flapping
  routes can be a serious concern with Internet
  core routers.
• CIDR allows routers to aggregate, or summarize,
  routing information and thus shrink the size of
  their routing tables.
• Just one address and mask combination can
  represent the routes to multiple networks.
• Used by IGP routers within an AS and EGP routers
  between AS.

19

• Without CIDR, a router must maintain individual
  routing table entries for these class B networks.

With CIDR, a router can summarize these routes
into eight networks by using a 13-bit prefix
172.24.0.0 /13
Steps
1. Count the number of left-most matching bits,
/13 2. Add all zeros after the last matching
bit 172.24.0.0 10101100
00011000 00000000 00000000
20
CIDR (Classless Inter-Domain Routing)

• By using a prefix address to summarizes routes,
  administrators can keep routing table entries
  manageable, which means the following
• More efficient routing
• A reduced number of CPU cycles when
  recalculating a routing table, or when sorting
  through the routing table entries to find a match
• Reduced router memory requirements
• Route summarization is also known as
• Route aggregation
• Supernetting
• Supernetting is essentially the inverse of
  subnetting.
• CIDR moves the responsibility of allocation
  addresses away from a centralized authority
  (InterNIC).
• Instead, ISPs can be assigned blocks of address
  space, which they can then parcel out to
  customers.

21
ISP/NAP Hierarchy - The Internet Still
hierarchical after all these years. Jeff Doyle
(Tries to be anyways!)
22
Supernetting Example

• Company XYZ needs to address 400 hosts.
• Its ISP gives them two contiguous Class C
  addresses
• 207.21.54.0/24
• 207.21.55.0/24
• Company XYZ can use a prefix of 207.21.54.0 /23
  to supernet these two contiguous networks.
  (Yielding 510 hosts)
• 207.21.54.0 /23
• 207.21.54.0/24
• 207.21.55.0/24

23 bits in common
23
Supernetting Example

• With the ISP acting as the addressing authority
  for a CIDR block of addresses, the ISPs customer
  networks, which include XYZ, can be advertised
  among Internet routers as a single supernet.

24
CIDR and the Provider
Another example of route aggregation.
25
CIDR and the provider
200.199.48.0/25
Summarization from the customer networks to
their provider.
200.199.56.0/23

• Even Better
• 200.199.48.32/27 11001000 11000111 00110000 0
  0100000
• 200.199.48.64/27 11001000 11000111 00110000 0
  1000000
• 200.199.48.96/27 11001000 11000111 00110000 0
  1100000
• 200.199.48.0/25 11001000 11000111 00110000 0
  0000000
• (As long as there are no other routes
  elsewhere within this range, well)
• 200.199.56.0/24 11001000 11000111 0011100 0
  00000000
• 200.199.57.0/24 11001000 11000111 0011100 1
  00000000
• 200.199.56.0/23 11001000 11000111 0011100 0
  00000000

26
CIDR and the provider
200.199.48.0/25
Further summarization happens with the next
upstream provider.
200.199.56.0/23

• 200.199.48.0/25 11001000 11000111 0011 0000
  00000000
• 200.199.49.0/25 11001000 11000111 0011 0001
  00000000
• 200.199.56.0/23 11001000 11000111 0011 1000
  00000000
• 200.199.48.0/20 11001000 11000111 0011 0000
  00000000
• 20 bits in common

27
CIDR Restrictions

• Dynamic routing protocols must send network
  address and mask (prefix-length) information in
  their routing updates.
• In other words, CIDR requires classless routing
  protocols for dynamic routing.
• However, you can still configure summarized
  static routes, after all, that is what a
  0.0.0.0/0 route is.

28
Summarized and Specific Routes Longest-bit
Match (more later)
Merida
Summarized Update
Specific Route Update
172.16.0.0/16
172.16.5.0/24
172.16.5.0/24
172.16.1.0/24
Quito
Cartago
172.16.2.0/24
172.16.10.0/24

• Merida receives a summarized /16 update from
  Quito and a more specific /24 update from
  Cartago.
• Merida will include both routes in the routing
  table.
• Merida will forward all packets matching at least
  the first 24 bits of 172.16.5.0 to Cartago
  (172/16/5/0/24), longest-bit match.
• Merida will forward all other packets matching at
  least the first 16 bits to Quito (172.16.0.0/16).

29
Short Term Solutions IPv4 Enhancements

• CIDR (Classless Inter-Domain Routing) RFCs
  1517, 1518, 1519, 1520
• VLSM (Variable Length Subnet Mask) RFC 1009
• Private Addressing - RFC 1918
• NAT/PAT (Network Address Translation / Port
  Address Translation) RFC

30
VLSM (Variable Length Subnet Mask)

• Limitation of using only a single subnet mask
  across a given network-prefix (network address,
  the number of bits in the mask) was that an
  organization is locked into a fixed-number of of
  fixed-sized subnets.
• 1987, RFC 1009 specified how a subnetted network
  could use more than one subnet mask.
• VLSM Subnetting a Subnet
• If you know how to subnet, you can do VLSM!

31
VLSM Simple Example
1st octet
2nd octet
3rd octet
4th octet
10.0.0.0/8
10
Host
Host
Host
10.0.0.0/16
10
Subnet
Host
Host
10.0.0.0/16
10
0
Host
Host
10.1.0.0/16
10
1
Host
Host
10.2.0.0/16
10
2
Host
Host
10.n.0.0/16
10

Host
Host
10.255.0.0/16
10
255
Host
Host

• Subnetting a /8 subnet using a /16 mask gives us
  256 subnets with 65,536 hosts per subnet.
• Lets take the 10.2.0.0/16 subnet and subnet it
  further

32
VLSM Simple Example
Network
Subnet
Host
Host
10.2.0.0/16
10
2
Host
Host
10.2.0.0/24
10
2
Subnet
Host
10.2.0.0/24
10
2
0
Host
10.2.1.0/24
10
2
1
Host
10.2.n.0/24
10
2

Host
10.2.255.0/24
10
2
255
Host

• Note 10.2.0.0/16 is now a summary of all of the
  10.2.0.0/24 subnets.
• Summarization coming soon!

33
VLSM Simple Example

• 10.0.0.0/8 subnetted using /16
• Subnet 1st host Last host
  Broadcast
• 10.0.0.0/16 10.0.0.1 10.0.255.254
  10.0.255.255
• 10.1.0.0/16 10.1.0.1 10.1.255.254
  10.1.255.255
• 10.2.0.0/16 sub-subnetted using /24
• Subnet 1st host Last host
  Broadcast
• 10.2.0.0/24 10.2.0.1 10.2.0.254
  10.2.0.255
• 10.2.1.0/24 10.2.1.1 10.2.1.254
  10.2.1.255
• 10.2.2.0/24 10.2.2.1 10.2.2.254
  10.2.2.255
• Etc.
• 10.2.255.0/24 10.2.255.1 10.2.255.254
  10.2.255.255
• 10.3.0.0/16 10.3.0.1 10.3.255.254
  10.0.255.255
• Etc.
• 10.255.0.0/16 10.255.0.1 10.255.255.254
  10.255.255.255

34
VLSM Simple Example
An example of VLSM, NOT of good network design.

• Subnets
• 10.0.0.0/16
• 10.1.0.0/16
• 10.2.0.0/16
• 10.2.0.0/24
• 10.2.1.0/24
• 10.2.2.0/24
• Etc.
• 10.2.255.0/24
• 10.3.0.0/16
• Etc.
• 10.255.0.0/16

10.2.0.0/24
10.1.0.0/16
10.7.0.0/16
10.2.1.0/24
10.3.0.0/16
10.2.6.0/24
10.2.8.0/24
10.8.0.0/16
10.4.0.0/16
10.5.0.0/16
10.2.4.0/24
10.6.0.0/16
10.2.3.0/24
10.2.5.0/24

• Your network can now have 255 /16 subnets with
  65,534 hosts each AND 256 /24 subnets with 254
  hosts each.
• All you need to make it work is a classless
  routing protocol that passes the subnet mask with
  the network address in the routing updates.
• Classless routing protocols RIPv2, EIGRP, OSPF,
  IS-IS, BGPv4 (coming)

35
Another VLSM Example using /30 subnets
207.21.24.0/24 network subnetted into eight /27
(255.255.255.224) subnets
207.21.24.192/27 subnet, subnetted into eight /30
(255.255.255.252) subnets

• This network has seven /27 subnets with 30 hosts
  each AND eight /30 subnets with 2 hosts each.
• /30 subnets are very useful for serial networks.

36

• 207.21.24.192/27 207.21.24. 11000000
  
• 
  /30 Hosts Bcast
  2 Hosts
• 0 207.21.24.192/30 207.21.24. 110 00000
  01 10 11 .193 .194
• 1 207.21.24.196/30 207.21.24. 110 00100
  01 10 11 .197 .198
• 2 207.21.24.200/30 207.21.24. 110 01000
  01 10 11 .201 .202
• 3 207.21.24.204/30 207.21.24. 110 01100
  01 10 11 .205 .206
• 4 207.21.24.208/30 207.21.24. 110 10000
  01 10 11 .209 .210
• 5 207.21.24.212/30 207.21.24. 110 10100
  01 10 11 .213 .214
• 6 207.21.24.216/30 207.21.24. 110 11000
  01 10 11 .217 .218
• 7 207.21.24.220/30 207.21.24. 110 11100
  01 10 11 .221 .222

37
207.21.24.192/30
207.21.24.204/30
207.21.24.216/30
207.21.24.128/27
207.21.24.96/27
207.21.24.64/27
207.21.24.208/30
207.21.24.212/30
207.21.24.196/30
207.21.24.200/30
207.21.24.32/27
207.21.24.0/27
207.21.24.160/27
207.21.24.224/27

• This network has seven /27 subnets with 30 hosts
  each AND seven /30 subnets with 2 hosts each (one
  left over).
• /30 subnets with 2 hosts per subnet do not waste
  host addresses on serial networks .

38
VLSM and the Routing Table (more later)
Displays one subnet mask for all child routes.
Classful mask is assumed for the parent route.

• Routing Table without VLSM
• RouterXshow ip route
• 207.21.24.0/27 is subnetted, 4 subnets
• C 207.21.24.192 is directly connected,
  Serial0 
• C 207.21.24.196 is directly connected,
  Serial1
• C 207.21.24.200 is directly connected,
  Serial2
• C 207.21.24.204 is directly connected,
  FastEthernet0
• Routing Table with VLSM
• RouterXshow ip route
• 207.21.24.0/24 is variably subnetted, 4
  subnets, 2 masks
• C 207.21.24.192 /30 is directly connected,
  Serial0 
• C 207.21.24.196 /30 is directly connected,
  Serial1
• C 207.21.24.200 /30 is directly connected,
  Serial2
• C 207.21.24.96 /27 is directly connected,
  FastEthernet0

Each child routes displays its own subnet mask.
Classful mask is included for the parent route.

• Parent Route shows classful mask instead of
  subnet mask of the child routes.
• Each Child Routes includes its subnet mask.

39
Final Notes on VLSM

• Whenever possible it is best to group contiguous
  routes together so they can be summarized
  (aggregated) by upstream routers. (coming soon!)
• Even if not all of the contiguous routes are
  together, routing tables use the longest-bit
  match which allows the router to choose the more
  specific route over a summarized route.
• Coming soon!
• You can keep on sub-subnetting as many times and
  as deep as you want to go.
• You can have various sizes of subnets with VLSM.

40
Route flapping

• Route flapping occurs when a router interface
  alternates rapidly between the up and down
  states.
• Route flapping, and it can cripple a router with
  excessive updates and recalculations.
• However, the summarization configuration prevents
  the RTC route flapping from affecting any other
  routers.
• The loss of one network does not invalidate the
  route to the supernet.
• While RTC may be kept busy dealing with its own
  route flap, RTZ, and all upstream routers, are
  unaware of any downstream problem.
• Summarization effectively insulates the other
  routers from the problem of route flapping.

41
Short Term Solutions IPv4 Enhancements

• CIDR (Classless Inter-Domain Routing) RFCs
  1517, 1518, 1519, 1520
• VLSM (Variable Length Subnet Mask) RFC 1009
• Private Addressing - RFC 1918
• NAT/PAT (Network Address Translation / Port
  Address Translation) RFC

42
Private IP addresses (RFC 1918)

• If addressing any of the following, these private
  addresses can be used instead of globally unique
  addresses
• A non-public intranet
• A test lab
• A home network
• Global addresses must be obtained from a provider
  or a registry at some expense.

43
Discontiguous subnets

• Mixing private addresses with globally unique
  addresses can create discontiguous subnets.
  Not the main cause however
• Discontiguous subnets, are subnets from the same
  major network that are separated by a completely
  different major network or subnet.
• Question If a classful routing protocol like
  RIPv1 or IGRP is being used, what do the routing
  updates look like between Site A router and Site
  B router?

44
Discontiguous subnets

• Classful routing protocols, notably RIPv1 and
  IGRP, cant support discontiguous subnets,
  because the subnet mask is not included in
  routing updates.
• RIPv1 and IGRP automatically summarize on
  classful boundaries.
• Site A and Site B are all sending each other the
  classful address of 207.21.24.0/24.
• A classless routing protocol (RIPv2, EIGRP, OSPF)
  would be needed
• to not summarize the classful network address and
  
• to include the subnet mask in the routing updates.

45
Discontiguous subnets

• RIPv2 and EIGRP automatically summarize on
  classful boundaries.
• When using RIPv2 and EIGRP, to disable automatic
  summarization (on both routers)
• Router(config-router)no auto-summary
• SiteB now receives 207.21.24.0/27
• SiteB now receives 207.21.24.32/27

46
Short Term Solutions IPv4 Enhancements

• CIDR (Classless Inter-Domain Routing) RFCs
  1517, 1518, 1519, 1520
• VLSM (Variable Length Subnet Mask) RFC 1009
• Private Addressing - RFC 1918
• NAT/PAT (Network Address Translation / Port
  Address Translation) RFC

47
Network Address Translation (NAT)

• NAT Network Address Translatation
• 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.

48
Network Address Translation (NAT)
2.2.2.2 TCP Source Port 1923
TCP Source Port 1026
2.2.2.2 TCP Source Port 1924
TCP Source Port 1026

• 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 global address.
• This is sometimes called a many-to-one NAT.
• With PAT, or address overloading, literally
  hundreds of privately addressed nodes can access
  the Internet using only one global address.
• The NAT router keeps track of the different
  conversations by mapping TCP and UDP port numbers.

49
Using IP unnumbered

• There are certain drawbacks that come with using
  IP unnumbered
• The use of ping cannot determine whether the
  interface is up because the interface has no IP
  address.
• A network IOS image cannot boot over an
  unnumbered serial interface.
• IP security options cannot be supported on an
  unnumbered interface. 

50
DHCP

• DHCP overview
• DHCP operation
• Configuring IOS DHCP server
• Easy IP

51
DHCP overview

• Administrators set up DHCP servers to assign
  addresses from predefined pools. DHCP servers can
  also offer other information
• DNS server addresses
• WINS server addresses
• Domain names
• Most DHCP servers also allow the ability to
  define specifically what client MAC addresses can
  be serviced and to automatically assign the same
  number to a particular host each time.
• Note BootP was originally defined in RFC 951 in
  1985. It is the predecessor of DHCP, and it
  shares some operational characteristics. Both
  protocols use UDP ports 67 and 68, which are well
  known as BootP ports because BootP came before
  DHCP.

52
DHCP operation

• The client sends a DHCPREQUEST broadcast to all
  nodes.
• If the client finds the offer agreeable, it will
  send another broadcast.
• This broadcast is a DHCPREQUEST, specifically
  requesting those particular IP parameters.
• Why does the client broadcast the request instead
  of unicasting it to the server?
• A broadcast is used because the very first
  message, the DHCPDISCOVER, may have reached more
  than one DHCP server.
• After all, it was a broadcast. If more than one
  server makes an offer, the broadcasted
  DHCPREQUEST lets the servers know which offer was
  accepted, which is usually the first offer
  received.

53
Configuring IOS DHCP server
Basic
More options

• Note The network statement enables DHCP on any
  router interfaces belonging to that network.

54
Configuring IOS DHCP server
55
Easy IP
56
Using helper addresses
57
Configuring IP helper addresses
By default, the ip helper-address command
forwards the eight UDPs services.
58
Configuring IP helper addresses
Broadcast
Unicast

• 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

59
Configuring IP helper addresses
Broadcast
Unicast

• Helper address configuration that relays
  broadcasts to all servers on the segment.
• RTA(config)interface e0
• RTA(config-if)ip helper-address 172.24.1.255
• But will RTA forward the broadcast?

60
Directed Broadcast

• Notice that the RTA interface e3, which connects
  to the server farm, is not configured with helper
  addresses.
• However, the output shows that for this
  interface, directed broadcast forwarding is
  disabled.
• This means that the router will not convert the
  logical broadcast 172.24.1.255 into a physical
  broadcast with a Layer 2 address of
  FF-FF-FF-FF-FF-FF.
• To allow all the nodes in the server farm to
  receive the broadcasts at Layer 2, e3 will need
  to be configured to forward directed broadcasts
  with the following command
• RTA(config)interface e3
• RTA(config-if)ip directed-broadcast

61
Configuring IP helper addresses
L3 Broadcast
L2 Broadcast

• Helper address configuration that relays
  broadcasts to all servers on the segment.
• RTA(config)interface e0
• RTA(config-if)ip helper-address 172.24.1.255
• RTA(config)interface e3
• RTA(config-if)ip directed-broadcast

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IP address issues solutions

• This module has shown that IPv4 addressing faces
  two major issues
• The depletion of addresses, particularly the key
  medium-sized space
• The pervasive growth of Internet routing tables
• In 1994, the Internet Engineering Task Force
  (IETF) proposed IPv6 in RFC 1752 and a number of
  working groups were formed in response. IPv6
  covers issues such as the following
• Address depletion
• Quality of service
• Address autoconfiguration
• Authentication
• Security
• It will not be easy for organizations deeply
  invested in the IPv4 scheme to migrate to a
  totally new architecture. As long as IPv4, with
  its recent extensions and CIDR enabled hierarchy,
  remains viable, administrators will shy away from
  adopting IPv6. A new IP protocol requires new
  software, new hardware, and new methods of
  administration. It is likely that IPv4 and IPv6
  will coexist, even within an autonomous system,
  for years to come. 

63
IPv6

• Three general types of addresses exist
• Unicast An identifier for a single interface. A
  packet sent to a unicast address is delivered to
  the interface identified by that address.
• Anycast An identifier for a set of interfaces
  that typically belong to different nodes. A
  packet sent to an anycast address is delivered to
  the nearest, or first, interface in the anycast
  group.
• Multicast An identifier for a set of interfaces
  that typically belong to different nodes. A
  packet sent to a multicast address is delivered
  to all interfaces in the multicast group.

64
IPv6

• To write 128-bit addresses so that they are
  readable to human eyes, the IPv6 architects
  abandoned dotted decimal notation in favor of a
  hexadecimal format.
• Therefore, IPv6 is written as 32 hex digits, with
  colons separating the values of the eight 16-bit
  pieces of the address.

65
IPv6

• IP v6, or IPng (IP the Next Generation) uses a
  128-bit address space, yielding
• 340,282,366,920,938,463,463,374,607,431,768,2
  11,456
• possible addresses.

66
Summary

• This module described how all of the following
  could enable more efficient use of IP addresses
• Subnet masks
• VLSMs
• Private addressing
• Network address translation (NAT)