4a1

1
Chapter 4 Network Layer

• Chapter goals
• understand principles behind network layer
  services
• routing (path selection)
• dealing with scale
• how a router works
• advanced topics IPv6, mobility
• instantiation and implementation in the Internet

2
Chapter 4 Network Layer

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

3
Network layer

• takes segments from transport layer
• on sending side, encapsulates segments into
  datagrams
• sends the datagrams to its nearby router
• on rcving side, extracts the transport-layer
  segments
• delivers segments to transport layer
• network layer protocols in every host and router
• router examines header fields in all IP datagrams
  passing through it

4
Key network-layer functions

• Analogy
• routing process of planning trip from source to
  dest
• forwarding process of getting through single
  interchange
• Packet switch
• link-layer switch the forwarding is based on the
  link-layer address
• router the forwarding is based on the
  network-layer address

• Forwarding and routing
• forwarding move packets from routers input to
  appropriate router output
• routing determine route taken by packets from
  source to dest
• routing algorithms

5
Interplay between routing and forwarding
6
Connection setup

• 3rd important function in some network
  architectures
• ATM, frame relay, X.25
• Before datagrams flow, two hosts and intervening
  routers establish virtual connection
• routers get involved
• Network and transport layer connection service
• network between two hosts
• transport between two processes

7
Network service model
Q What service model for channel transporting
datagrams from sender to rcvr?

• Example services for individual datagrams
• Guaranteed delivery
• Guaranteed delivery with bounded delay (for
  example, within 100 msec)

• Example services for a flow of datagrams
• In-order datagram delivery
• Guaranteed minimal bandwidth
• Guranted maximum jitter
• Restrictions on changes in inter-packet spacing

8
Network layer service models
Guarantees ?
Network Architecture Internet ATM ATM ATM ATM
Service Model best effort CBR VBR ABR UBR
Congestion feedback no (inferred via
loss) no congestion no congestion yes no
Bandwidth none constant rate guaranteed rate gua
ranteed minimum none
Loss no yes yes no no
Order no yes yes yes yes
Timing no yes yes no no

• Internet model being extended (chapter 7)
• Integrated service (Intserv)
• Differentiated service (Diffserv)

9
ATM network service model (1)

• constant bit rate (CBR) network service
• class A circuit emulation
• it is intended to emulate a copper wire or
  optical wire, suited for carrying real-time,
  constant-bit-rate audio and video traffic
  circuit emulation
• cell-transfer delay (CTD), cell-delay variation
  (CDV), and cell-loss rate (CLR) are guaranteed to
  be less than some specified values
• allocated transmission rate (peak cell rate, PCR)
  is defined for the connection and the sender is
  expected to offer data to the network at this
  rate

10
ATM network service model (2)

• variable bit rate (VBR) network service class B
• real-time VBR
• acceptable cell-loss rate, delay, and delay
  jitter are specified as in CBR service
• however, the actual source rate is allowed to
  vary according to parameters specified by the
  user to the network
• e.g., interactive compressed video (video
  conferencing)
• non-real-time VBR
• timely delivery is important but a certain amount
  of jitter can be tolerated
• e.g., multimedia email

11
ATM network service model (3)

• available bit rate (ABR) network service
• class C connection oriented data
• minimum cell transmission rate (MCR) is
  guaranteed
• if the network has enough free resources at a
  given time, a sender may actually be able to send
  traffic at a higher rate than the MCR
• congestion feedback from the network to the
  sender that controls how the sender should adjust
  its rate between the MCR and the PCR
• connection-oriented data
• unspecified bit rate (UBR) network service
• class D connectionless data
• with the exception of in-order delivery, it is
  equivalent to the Internet best-effort service
  model.
• connectionless data

12
Chapter 4 Network Layer

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

13
Network layer connection and connectionless
service

• The network-layer connection and connectionless
  services are analogous to the transport-layer
  services, but
• service
• in the network layer, it is host-to-host service
• in the transport layer, it is process-to-process
  service
• no choice
• in the network layer, network provides one or the
  other
• datagram network provides network-layer
  connectionless service
• virtual-circuit network provides network-layer
  connection service
• implementation
• in the network layer, connection-oriented service
  is implemented in the router (the network core)
• in the transport layer, it is implemented at the
  edge of the network

14
Virtual circuits

• source-to-dest path behaves much like telephone
  circuit
• performance-wise
• network actions along source-to-dest path

• call setup before data can flow, teardown for
  each call
• each packet carries VC identifier (not
  destination host ID)
• every router on source-dest path maintains
  state for each passing connection
• transport-layer connection only involved two end
  systems
• link, router resources (bandwidth, buffers) may
  be allocated to VC
• to get circuit-like performance

15
VC implementation

• A VC consists of
• a path between the source to destination hosts
• VC numbers, one number for each link along the
  path
• entries in forwarding tables in each router along
  the path
• A aacket belonging to a virtual curcuit carries a
  VC number in its header.
• Each intervening router must replace the VC
  number of each traversing packet with a new one.
• New VC number comes from the forwarding table

16
Forwarding table
Forwarding table in R1
Routers maintain connection state information!
17
Virtual circuits signaling protocols

• used to setup, maintain teardown VC
• used in ATM, frame-relay, X.25
• not used in todays Internet

6. Receive data
5. Data flow begins
4. Call connected
3. Accept call
1. Initiate call
2. incoming call
18
Datagram networks

• no call setup at network layer
• routers no state about end-to-end connections
• no network-level concept of connection
• packets forwarded using destination host address
• packets between same source-dest pair may take
  different paths

1. Send data
2. Receive data
19
Forwarding table

• Suppose that all destination addresses are 32
  bits
• There are more than 4 billion possible address

Destination Address Range
Link Interface
11001000 00010111 00010000 00000000
through
0
11001000 00010111 00010111 11111111
11001000 00010111 00011000 00000000
through
1
11001000 00010111 00011000 11111111
11001000 00010111 00011001 00000000
through
2
11001000 00010111 00011111 11111111
otherwise
3
20
Longest prefix matching
Examples DA 11001000 00010111 00010110
10100001 Which interface? DA 11001000
00010111 00011000 10101010 Which
interface?

21
Datagram or VC network why?

• Internet
• data exchange among computers
• elastic service, no strict timing req.
• smart end systems (computers)
• can adapt, perform control, error recovery
• simple inside network, complexity at edge
• many link types
• different characteristics
• uniform service difficult

• ATM
• evolved from telephony
• human conversation
• strict timing, reliability requirements
• need for guaranteed service
• dumb end systems
• telephones
• complexity inside network

22
Chapter 4 Network Layer

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

23
Router Architecture Overview

• two key router functions
• run routing algorithms/protocols (RIP, OSPF, BGP)
• forwarding datagrams from incoming to outgoing
  link
• four components of router
• input ports
• switching fabric
• output ports
• routing processors

24
Input Port Functions
physical layer bit-level reception
data link layer e.g., Ethernet

• decentralized switching
• given datagram dest., lookup output port using
  routing table in input port memory
• goal complete input port processing at line
  speed
• speeding routing table lookup
• binary search
• content addressable memory (CAM)
• caching recently accessed routing table entry
• if a packet is temporarily blocked from entering
  the switching fabric, the blocked packet must be
  queued

25
Three types of switching fabrics

• Switching via memory
• Switching via a bus
• Switching via an interconnection network

26
Switching via Memory

• First generation routers
• input port with arriving packet signals the
  routing processor via an interrupt
• the packet is copied from the input port into
  processor memory
• routing processor extracts the destination
  address from the header, look up an appropriate
  output port in the routing table, and copies the
  packet to the output port's buffer
• memory bandwidth is B packets/sec -gt switch
  throughput is less than B/2.

• Modern routers
• input port processor performs lookup, storing
  into memory
• e.g., Ciscos Catalyst 8500 series

27
Switching via Bus

• datagram from input port memory to output port
  memory via a shared bus
• bus contention switching bandwidth is limited
  to bus speed
• 1 Gbps bus, Cisco 1900 sufficient speed for
  access and enterprise routers (not regional or
  backbone)

28
Switching via an Interconnection Network

• overcome bus bandwidth limitations
• Delta, Omega networks, other interconnection nets
  initially developed to connect processors in
  multiprocessor computer architecture
• one current trend
• fragment a variable length IP datagram into
  fixed-length cells, and then tag and switch the
  cells through the interconnection network
• the cells are then reassembled into the original
  datagram at the output port.
• Cisco 12000 switches 60 Gbps through the
  interconnection network

29
Output Ports

• Buffering required when datagrams arrive from
  fabric faster than the transmission rate
• Packet scheduler chooses among queued datagrams
  for transmission
• first-come-first-served (FCFS) scheduling
• weighted fair queuing (WFQ)
• Packet scheduling plays a crucial role in
  providing quality-of-service (QoS) guarantees
  (Ch. 7)

30
Output port queueing

• buffering when arrival rate via switch exceeds
  output line speed
• queueing (delay) and loss due to output port
  buffer overflow!
• active queue management (AQM) algorithms
• random early detection (RED)

31
Input Port Queuing

• Fabric slower than input ports combined -gt
  queueing may occur at input queues
• Head-of-the-Line (HOL) blocking queued datagram
  at front of queue prevents others in queue from
  moving forward
• queueing delay and loss due to input buffer
  overflow!

32
Chapter 4 Network Layer

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

33
The Internet Network layer

• Three major components of the network layer
• network protocol IPv4, IPv6 for the Internet
  Protocol
• path determination component routing protocols
• facility to report errors in datagrams and
  respond to requests for certain network-layer
  information

Transport layer TCP, UDP
Network layer
Link layer
A look inside the Internets network layer
Physical layer
34
Chapter 4 Network Layer

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

35
IP datagram format

• how much overhead with TCP?
• 20 bytes of TCP
• 20 bytes of IP
• 40 bytes app layer overhead

36
IP Header

• Version number (4bits) 4 for IPv4 and 6 for IPv6
  
• Header length (4bits)
• number of 32-bit words in the header
• it limits the header length to 60 bytes
• TOS (type of service, 8bits)
• precedence (ignored today, 3 bits)
• TOS (RFC 1340, 1349) only 1 of 4 bits can be
  turned on
• 0000 - Normal service, 1000 - Minimize
  delay, 0100 - Maximize throughput,
• 0010 - Maximize reliability, 0001
  - Minimize monetary cost,
• MBZ(must be zero, 1 bits) Reserved for future
  use
• Datagram length (16 bits)
• Total length of the IP datagram in bytes.
• Maximum size of the datagram is 65535 bytes
• Identification (16 bits)
• it normally increments by 1 each time a datagram
  is sent
• Flags (3 bits)
• bit 0 reserved, must be zero
• bit 1 (DF) 0 - may fragment, 1 - don't fragment
• bit 2 (MF) 0 - last fragment, 1 - more
  fragments

37
IP Header (cont.)

• TTL (time to live, 8 bits) upper limit on the
  number of routers through which a datagram can
  pass
• sender decides the value of TTL
• this field is decremented by each router.
• if it reaches 0, the datagram must be discarded.
  ICMP message is sent to the sender
• Protocol (8 bits) demultiplex incoming datagrams
  according to protocol value
• 1 - ICMP, 2 - IGMP, 6 - TCP, 17
  UDP, 89 OSPF
• Header checksum (16 bits)
• checksum field 16-bit 1s complement sum
• IP header checksum checksum
• Source IP address and Destination IP address (32
  bits each)
• Options (variable length)
• security and handling restriction
• record route
• timestamp
• loose source routing,

38
IP Fragmentation Reassembly

• network links have MTU (maximum transfer unit)
• largest possible link-level frame.
• different link types, different MTUs
• large IP datagram divided (fragmented) within
  net
• one datagram becomes several datagrams
• reassembled only at final destination
• IP header bits used to identify, order related
  fragments

39
IP Fragmentation and Reassembly
4000 20 3980 bytes in data field
Assume MTU of forwarding link is 1500 Then, one
large datagram becomes several smaller datagrams
1st fragment 1480 bytes in data field
2nd fragment 1480 bytes in data field offset
1480/8 185
3rd fragment 3980 21480 1020 bytes in data
field

• Data in all but the last fragment should be a
  multiple of 8 bytes
• All data-link protocols supported by IP are
  supposed to have MTUs of at least 576 bytes.
  Thus, fragmentation can be entirely eliminated by
  using an MSS of 536 bytes, 20 bytes of TCP header
  and 20 bytes of IP header. This is why most TCP
  segments for bulk data transfer (such as with
  HTTP) are 512-536 bytes long.

40
Chapter 4 Network Layer

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

41
IPv4 Addressing

• interface connection between host, router and
  physical link
• routers typically have multiple interfaces
• host may have multiple interfaces
• IP addresses associated with interface, not host,
  router
• IP address 32-bit identifier for host, router
  interface
• typically written in dotted-decimal number
• each byte of the address is written in decimal
  form and is separated by a period ("dot")

42
Subnets

• IP address
• subnet part (high order bits)
• host part (low order bits)
• Whats a subnet?
• device interfaces with same subnet part of IP
  address
• can physically reach each other without
  intervening router
• a subnet is also called an IP network or simply a
  network
• e.g., 223.1.1.0/24, where the "/24" notation
  (subnet mask) indicates that the leftmost 24 bits
  of the 32-bit quantity define the subnet address
• any additional host attached to 223.1.1.0/24
  subnet has an address of the form 223.1.1.xxx

interface addresses and subnets
43
Subnets (cont.)

• How to find the subnets?
• To determine the subnets, detach each interface
  from its host or router, creating islands of
  isolated networks, with interfaces terminating
  the endpoints of the isolated networks.
• Each isolated network is called a subnet.

Three routers interconnecting six subnets
44
IP Addresses

• IP address a.b.c.d/x
• network address (network prefix)
• host address
• class-full addressing

45
IP addressing CIDR

• classful addressing
• inefficient use of address space, address space
  exhaustion
• e.g., class B net allocated enough addresses for
  65K hosts, even if only 2K hosts in that network
• CIDR Classless InterDomain Routing
• network portion of address of arbitrary length
• address format a.b.c.d/x, where x is the number
  of bits in network portion of address
• subnetting
• the division of the local part of the IP address
  into subnet ID and host ID, which can be chosen
  freely by the local administrator
• subnet mask 32-bit value containing 1 bits for
  the network ID and subnet ID, and 0 bits for the
  host ID

host part
subnet part
11001000 00010111 00010000 00000000
11111111 11111111 11111110 00000000
subnet mask
200.23.16.0/23
46
IP addresses how to get one?

• Q How does host get IP address?
• hard-coded by system admin in a file
• Wintel ??? ? ???? ?? ? ?????? ? ?? ? tcp/ip
• UNIX /etc/rc.config
• DHCP Dynamic Host Configuration Protocol
• dynamically get address from a server
• plug-and-play (more in next chapter)

47
IP addresses how to get one?
Q how does network get network part of IP
addr? A gets allocated portion of its ISPs
address space
ISP's block 11001000 00010111 00010000
00000000 200.23.16.0/20 organization 0
11001000 00010111 00010000 00000000
200.23.16.0/23 organization 1 11001000
00010111 00010010 00000000 200.23.18.0/23
organization 2 11001000 00010111 00010100
00000000 200.23.20.0/23 ...
..
. . organization
7 11001000 00010111 00011110 00000000
200.23.30.0/23
48
Hierarchical addressing route aggregation

• hierarchical addressing allows efficient
  advertisement of routing information
• this ability to use a single network prefix to
  advertise multiple networks is often referred to
  as address aggregation or route summarization

49
Hierarchical addressing more specific routes

• ISPs-R-Us has a more specific route to
  Organization 1
• when routers in the larger Internet see the
  address blocks 200.23.16.0/20 (from
  Fly-By-Night-ISP) and 200.23.18.0/23 (from
  ISPs-R-Us) and want to route to an address in the
  block 200.23.18.0/23, they will use a longest
  prefix matching rule, and route toward ISPs-R-Us

50
IP addressing the last word...

• Q How does an ISP get block of addresses?
• A ICANN Internet Corporation for Assigned Names
  and Numbers
• allocates addresses
• manages DNS
• assigns domain names, resolves disputes
• actual assignment of addresses is managed by
  regional Internet registries
• as of mid-2000, there are three such regional
  registries
• ARIN (American Registry for Internet Number,
  which handles registrations for North America)
• LACNIC (Latin American and Caribbean IP Address
  Regional Registry)
• AfriNIC (African Network Information Center)
• RIPE NCC (RIPE Network Corporation Center
  Europe, Middle East, Central Asia)
• APNIC (Asia Pacific Network Information Center)

51
NAT Network Address Translation
rest of Internet
local network (e.g., home network) 10.0.0/24
10.0.0.1
10.0.0.4
10.0.0.2
138.76.29.7
10.0.0.3
All datagrams leaving local network have same
single source NAT IP address 138.76.29.7, differe
nt source port numbers
Datagrams with source or destination in this
network have 10.0.0/24 address for source,
destination (as usual)
52
NAT Network Address Translation

• Motivation local network uses just one IP
  address as far as outside world is concerned
• no need to be allocated range of addresses from
  ISP - just one IP address is used for all devices
• can change addresses of devices in local network
  without notifying outside world
• can change ISP without changing addresses of
  devices in local network
• devices inside local net not explicitly
  addressable, visible by outside world (a security
  plus).

53
NAT Network Address Translation

• Implementation NAT router must
• outgoing datagrams replace (source IP address,
  port ) of every outgoing datagram to (NAT IP
  address, new port )
• remote clients/servers will respond using (NAT IP
  address, new port ) as destination addr.
• remember (in NAT translation table) every (source
  IP address, port ) to (NAT IP address, new port
  ) translation pair
• incoming datagrams replace (NAT IP address, new
  port ) in dest fields of every incoming datagram
  with corresponding (source IP address, port )
  stored in NAT table

54
NAT Network Address Translation
NAT translation table WAN side addr LAN
side addr
138.76.29.7, 5001 10.0.0.1, 3345

10.0.0.1
10.0.0.4
10.0.0.2
138.76.29.7
10.0.0.3
4 NAT router changes datagram dest addr
from 138.76.29.7, 5001 to 10.0.0.1, 3345
3 Reply arrives dest. address 138.76.29.7,
5001
55
NAT Network Address Translation

• 16-bit port-number field
• 60,000 simultaneous connections with a single
  WAN-side address!
• NAT is controversial
• port numbers are meant to be used for addressing
  process, not for addressing hosts
• routers should only process packets up to layer 3
• violates end-to-end argument
• address shortage should instead be solved by IPv6

56
Chapter 4 Network Layer

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

57
ICMP Internet Control Message Protocol

• used by hosts, routers, gateways to communicate
  network-level information
• error reporting unreachable host, network, port,
  protocol
• echo request/reply (used by ping)
• network-layer above IP
• ICMP msgs carried in IP datagrams
• ICMP error message type, code plus first 8 bytes
  of IP datagram causing error
• e.g., ping program sends an ICMP type 8 code 0
• destination sends an ICMP type 0 code 0 (echo
  reply)

Type Code description 0 0
echo reply (ping) 3 0 dest. network
unreachable 3 1 dest host unreachable
3 2 dest protocol unreachable 3 3
dest port unreachable 3 6 dest
network unknown 3 7 dest host unknown
4 0 source quench (congestion
control - not used) 8 0 echo
request (ping) 9 0 route advertisement
10 0 router discovery 11 0 TTL
expired 12 0 bad IP header
58
Traceroute and ICMP

• Source sends series of UDP segments to dest
• first has TTL 1
• second has TTL 2, etc.
• unlikely port number
• When nth datagram arrives to nth router
• router discards datagram
• and sends to source an ICMP message (type 11,
  code 0)
• message generally includes name of router and IP
  address
• when ICMP message arrives, source calculates RTT
• traceroute does this 3 times

• Stopping criterion
• UDP segment eventually arrives at destination
  host
• destination returns destination port
  unreachable ICMP message (type 3, code 3)
• when source gets this ICMP, stops.

59
Chapter 4 Network Layer

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats inside a router
• 4.4 IP Internet Protocol
• Datagram format
• IPv4 addressing
• ICMP
• IPv6

• 4.5 Routing algorithms
• Link state
• Distance Vector
• Hierarchical routing
• 4.6 Routing in the Internet
• RIP
• OSPF
• BGP
• 4.7 Broadcast and multicast routing

60
IPv6

• Initial motivation
• 32-bit address space completely allocated by 2008
• larger address 128 bits
• Additional motivation
• header format helps speed processing/forwarding
• header changes to facilitate QoS
• new anycast address route to best of several
  replicated servers
• IPv6 datagram format
• fixed-length 40 byte header
• no fragmentation allowed

40 bytes
61
IPv6 Header

• Version (4bits) IPv6 carries a value of 6 in
  this field
• Traffic class (8bits) this eight-bit field is
  similar in spirit to the TOS field in IPv4
• Flow label (20 bits) identify datagrams in same
  flow
• concept of flow not well defined

RFC 1752 and RFC 2460 it may be used by a source
to label sequences of packets for which it
requests special handling by the IPv6 routers,
such as non-default quality of service or
"real-time" service
62
IPv6 Header (cont.)

• Payload length (16 bits) unsigned integer giving
  the number of bytes in the IPv6 datagram
  following the fixed-length, 40-byte packet header
• Next header (8 bits) specifies the type of the
  following header.
• Hop limit (8 bits) it is decremented by one by
  each router that forwards the datagram. if the
  hop limit count reaches zero, the datagram is
  discarded
• Source and destination address IPv6 128-bit
  address are described in RFC 2373.
• Data the payload portion of the IPv6 datagram.
  when the datagram reaches its destination, the
  payload will be removed from the IP datagram and
  passed on to the protocol specified in the next
  header field.

63
IPv6 Address

• IPv6 address is 16 bytes (128 bits) long
• colon hexadecimal notation (or colon hex)
• 16-bit quantity is represented in hexadecimal
  separated by colon
• 68E68C64FFFFFFFF0118096AFFFF
• zero compression
• FF05000000B3
• ? FF05B3
• partial address
• 12ABCD300000/60
• ? 12AB00000000CD3 (first 60 bits)

64
Other Changes from IPv4

• Fragmentation/Reassembly
• IPv6 does not allow for fragmentation at
  intermediate routers
• if an IPv6 datagram is too large to be forwarded
  over the link, the router simply drops the
  datagram and sends a packet too big" ICMP error
  message back to the sender. the sender can then
  resend the data, using a smaller IP datagram
  size.
• Checksum removed entirely to reduce processing
  time at each hop
• Options allowed, but outside of header,
  indicated by next header field
• ICMPv6 (RFC 2463) new version of ICMP
• additional message types, e.g. packet too big,
  unrecognized IPv6 options"
• subsumes the functionality of Internet Group
  Management Protocol (IGMP)

65
Transition From IPv4 To IPv6

• not all routers can be upgraded simultaneous
• no flag days
• how will the network operate with mixed IPv4 and
  IPv6 routers?
• Two proposed approaches
• dual stack
• IPv6-capable nodes also have a complete IPv4
  implementation as well
• referred to as IPv6/IPv4 node in RFC 1933
• IPv6/IPv4 nodes must have both IPv6 and IPv4
  addresses
• tunneling
• IPv6 carried as payload in IPv4 datagram among
  IPv4 routers

66
Dual Stack Approach
IPv6
IPv6
IPv6
IPv6
IPv4
IPv4
A-to-B IPv6
B-to-C IPv4
B-to-C IPv6
B-to-C IPv4
67
Tunneling
IPv6 inside IPv4
tunnel
Logical view
IPv6
IPv6
IPv6
IPv6
Physical view
IPv6
IPv6
IPv6
IPv6
IPv4
IPv4
SrcB Dest E
SrcB Dest E
Flow X Src A Dest F data
Flow X Src A Dest F data
A-to-B IPv6
E-to-F IPv6
B-to-C IPv6 inside IPv4
B-to-C IPv6 inside IPv4
68
TCP/IP Layering
69
Demultiplexing of a Received Ethernet Frame