More on the IP

1
More on the IP

• Internet Protocol

2
Internet Layer Process

• Transport layer process passes EACH TCP segment
  to the internet layer process for delivery

Transport LayerProcess
TCP segment
Internet LayerProcess
3
IP Connectionless Service

• The Internet Protocol (IP)
• Internet layer protocol
• Governs transmission between router and host
• Governs transmission between pairs of routers
• Gives end-to-end route across many routers

User PC
Webserver
Router
Router
4
IP Connectionless Service

• The Internet Protocol (IP)
• IP messages are called IP packets
• No connections are established
• No open, close, error correction, flow control
• Low overhead

IP Packet
Internet Process
Internet Process
5
IP Connectionless Service

• IP is unreliable
• No error handling (Let TCP catch errors!)
• No sequence numbers, so no way to put arriving IP
  packets in order (Let TCP put the TCP segments
  these IP packets contain in order!)

IP Packet
Internet Process
Internet Process
6
TCP/IP Partnership

• TCP checks for errors once, at the destination
  host
• IP is used in many hops between routers
• Not checking for errors at each step greatly
  reduces overall processing work
• Reduces router costs

Check Only Once
Transport
Transport
Internet
Internet
Internet
Host
Router
Host
7
Connectionless IP

• IP is unreliable (does not catch errors)
• But this is not bad
• First, errors are corrected--at the next-higher
  layer (transport) if TCP is used
• Second, avoiding error correction at each hop
  between routers lowers router costs
• Far less expensive to correct errors on one
  destination host than on many routers along the
  way

8
IP Addresses and Router Forwarding

• Routers use the destination IP address of an
  incoming packet in the router forwarding
  decision, that is, to decide what output port to
  use to send the packet back out to the
  destination host or to another router (B, C or D?)

B
B?
D?
Router A
D
Packet
C?
C
9
Router Delivery

• If Destination Host is On the Source Hosts
  Subnet, Source Host Delivers the Packet Directly
• No router is involved

Source Host
Subnet
Subnet
Destination Host
10
Router Delivery

• If Destination Host is NOT On the Source Hosts
  Subnet, Source Host Sends the Packet to a Router
  for Delivery

Subnet
Subnet
11
Router Delivery

• If Destination Host is On One of the Routers
  Subnets, the Router Sends the Packet to the
  Destination Host for Delivery

Subnet
Subnet
12
Router Delivery

• If Destination Host is NOT On One of the Routers
  Subnets, the Router Sends the Packet to a
  Next-Hop Router for Delivery
• May have to choose among several possible
  next-hop routers for delivery

Subnet
Subnet
13
Router Delivery

• Border Routers Connect Networks, Not Subnets
• Select between next-hop router on own network or
  on another network

Own Network
Other Network
14
IP Addresses and Router Forwarding

• Routers look at destination IP address of packet
  to make decisions
• What do I do with this packet, based upon its IP
  destination address

B
B?
D?
Router A
D
Packet
C?
C
15
IP Address

• 32-bit Strings
• Often given in dotted decimal notation
  128.171.17.13
• Fits into 32-bit source and destination address
  field of IP headers

IP Packet
32-bit Source and Destination Addresses
16
IP Addresses
City 1
Letter
City 2
City 3

• Many Addressing Systems Use Hierarchical
  Addressing
• Postal delivery city, street address
• Post office looks at city first
• If not P.O.s city, put in bag for other city
• If in P.O.s city, put in bag for sorting by
  street address
• Hierarchical addressing greatly speeds sorting at
  each post office
• Imagine if we needed a sorting bin for each
  address in the country!

17
IP Addresses

• For IP, Routers Take the Place of Post Offices
• There are hundreds of millions of IP addresses on
  the Internet
• Routers cannot store decision rules for reaching
  each address individually
• So router makes decisions first based on the
  network of subnet containing the destination host
• This is the router forwarding decision

18
IP Addresses
Network
Network

• The Internet is Made of Many Individual Networks
  Owned by Different Organizations
• For instance, there is the University of Hawaii
  network
• Note that Network is an organizational
  (concept)
• Border routers connect different networks

19
IP Addresses
Subnet
Subnet

• Most large organizations divide their networks
  into subnets managed by smaller units
• At the University of Hawaii, the College of
  Business Administration is a subnet
• Subnet is also an organizational concept
• Internal routers within organizations connect
  subnets

20
IP Addresses

• Each Organization is Given a Network Part Number
• For the University of Hawaii, this is 128.171
• All IP Addresses in that organizations network
  begin with that Network Part

Network Part
IP Address
128.171
21
IP Addresses

• Network Parts can be 8 to 24 bits long
• For University of Hawaii, it is 16 bits long
• 16 bits is only an example

Network Part (8 to 24 bits)
IP Address
22
IP Addresses
Network
Network

• Between different organization networks, routers
  look first at the Network Part of an arriving IP
  packets destination address
• If the network part is not that of the
  organization, the router cannot deliver the IP
  packet locally
• Passes the IP packet on to another router, called
  a next-hop router, to move the IP packet closer
  to the destination host

Network Part
23
Assigning Network Parts

• Organization applies to an Internet IP address
  registrar
• Registrar gives organization a network part
• Organization assigns the local part to its hosts
  internally
• Only large organizations and ISPs get network
  parts

128.171.17.13
Registrar
Firm
128.171
128.171.123.130
24
IP Addresses

• Network Part is Followed by a Subnet Part
• Identifies the subnet within the network
• Remaining bits are the Host Part, designating a
  particular host on that subnet

Network Part
Subnet Part
Host Part
IP Address (32 bits total)
25
Assigning Parts

• Example
• IP address registrar gave the University of
  Hawaii the network part 128.171
• UH gave the College of Business Administration
  the subnet part 17
• College of Business Administration gave the host
  part 13 to a computer it later gave the host name
  voyager.cba.hawaii.edu
• So the computers IP address became 128.171.17.13.

26
Assigning Subnet Parts

• Organization Assigns Subnet Parts
• Assigns subnet parts to suborganizations
• Suborganization assigns host bits to hosts

128.171
128.171.17.13
Suborganization
Registrar
Firm
128.171.17.13
Host
27
IP Addresses
Subnet
Subnet

• Within an organizational Network
• Router looks at Network Plus Subnet Part Combined
• If destination host is on a subnet attached to
  the router, delivers the IP packet to the host
• Otherwise, passes the packet on to a next-hop
  router

Network Part
Subnet Part
Host Part
IP Address (32 bits total)
28
Importance of Part Sizes

• Determine Number of Possible Networks, Subnets,
  or Hosts
• If There are N Bits in the Part, there can be 2N
  possible Networks, Subnets, or Hosts
• Actually, 2N-2
• All zeros cannot be used for a part
• All ones cannot be used for a part
• Example if part has 8 bits, 28-2 possibilities
  (254)

29
Masks

• Problem Just looking at an IP address does not
  tell you what bits belong to each part
• Solution Create a second 32-bit number, a mask,
  to tell the size of
• The network part for border router decisions
• The network plus subnet parts for internal router
  decisions

30
Masks

• Two Types Network Masks and Subnet Masks
• Network Mask Tells the Length of the Network Part
• Subnet Mask Tells the length of the Network Plus
  Subnet Parts (not just subnet part)
• IP Address will be paired with one or the other,
  but not both simultaneously
• The correct pairing happens automatically

31
Masks

• Masks Begin with 1s, End with 0s (11100)
• For network masks, 1s are in Network Part bits
  0s are in Subnet and Host Parts
• For subnet masks, 1s are in Network and Subnet
  Parts 0s are in Host part
• Again, always total 32 bits

11111111111111110000000000000000
32
Masks

• IP Address-Mask Pairs often Written with Prefix
  Notation
• 128.171.17.13/16
• 16 means that the mask has 16 initial 1s
• Total number of bits is 32 in an IP address, so
  there must be 16 trailing 0s

11111111111111110000000000000000
33
IP Address Classes

• How large is the network part in an IP address?
• Today we use network masks to tell
• Originally, IP had address classes with fixed
  numbers of bits in the network part
• Class A 8 bits (24 bits in local part)
• Class B 16 bits (16 bits in local part)
• Class C 24 bits (8 bits in local part)

34
Class A IP Address

• IP address begins with 0
• 7 remaining bits in network part
• Only 128 possible Class A networks
• Really, 127 because all zeros is not allowed
• 24 bits in local part
• Over 16 million hosts per Class A network!
• All Class A network parts are assigned or reserved

35
Class B IP Address

• IP address begins with 10 (1st zero in 2nd
  position)
• 14 remaining bits in network part
• Over 16,000 possible Class B networks
• 16 bits in local part
• Over 65,000 possible hosts
• A good trade-off between number of networks and
  hosts per network
• Most have been assigned

36
Class C IP Address

• IP address begins with 110 (1st zero in 3d
  position)
• 21 more bits in network part
• Over 2 million possible Class C networks!
• 8 bits in local part
• Only 254 possible hosts per Class C network!
• Unpopular, because even firms with 400 hosts
  cannot use them

37
CIDR
New Not in Book

• If a firm has 400 hosts, must get a whole Class B
  address, wasting most of the 65,000 addresses in
  such networks
• By the early 1990s, we were running out of Class
  B Internet addresses, and most firms were too
  large for Class C addresses
• This is why Classless InterDomain Routing (CIDR)
  has replaced class addressing

38
CIDR
New Not in Book

• CIDR does not limit the network part to 8, 16, or
  24 bits
• For a firm with 400 hosts, prefix can be, say
  /22, allowing 10 host bits and therefore over
  1,000 addresses
• A Class B address is not needed
• Has temporarily solved the problem of running out
  of IP addresses

39
Class D IP Address

• IP address begins with 1110
• Used for multicasting, not defining networks
• Sending message to group of hosts
• Not just to one (unicasting)
• Not ALL hosts (broadcasting)
• Say to send a videoconference stream to a group
  of receivers

40
Class D IP Address

• All hosts in a multicast group listen for this
  multicast address as well as for their specific
  own host IP address

In Group Accept
Packets to Multicast Address
Not in Group Reject
In Group Accept
41
Multicasting

• Traditionally, unicasting and broadcasting
• Unicasting send to one host
• Broadcasting send to ALL hosts
• Multicasting
• Send to SOME hosts
• 500 stations viewing a video course
• 50 computers getting software upgrades
• Standards exist and are improving
• Not widely implemented yet

42
Why Multicasting

• Do not need to send an IP packet to each host
• Routers split when needed
• Reduces traffic

Multiple Packets
Single Packet
43
Mask Operations

• Masks were introduced in Chapter 3
• IP addresses alone do not tell you the size of
  their network or subnet parts
• Network Mask
• Has 1s in the network part
• Has 0s in the remaining bits
• Subnet Mask
• Has 1s in the network plus subnet parts
• Has 0s in the remaining bits

44
Mask Operations

• Based on Logical AND
• Both must be true (1) for the result to be true
  (1)
• Example
• 1010101010 Data
• 1111100000 Mask
• 1010100000 Result

45
Mask Operations

• Based on Logical AND
• If mask bit is 1, get back original data
• If mask bit is 0, bet back zero
• Example
• 1010101010 Data
• 1111100000 Mask
• 1010100000 Result

46
Mask Operations

• IP packet arrives at a router
• Router sees destination IP address
• 11111111 01000000 10101010 00000000
• Compares to each router forwarding table row
• Address Part in First Entry
• 11111111 01000000 00000000 00000000
• Mask in First Entry
• 11111111 11100000 00000000 00000000

47
Mask Operations

• Mask the IP destination Address
• 11111111 01000000 10101010 00000000 (IP address)
• 11111111 11100000 00000000 00000000 (mask)
• 11111111 01000000 00000000 00000000 (result)
• Compare Result with First Entry Address part
• 11111111 01000000 00000000 00000000 (address
  part)
• 11111111 01000000 00000000 00000000 (result)
• The Entry is a Match!

48
Mask Operations

• Recap
• Read destination IP address of incoming IP packet
• For each entry in the router forwarding table
• Read the mask (prefix)
• Mask the incoming IP address
• Compare the result with the entrys IP address
  part
• Do they match or not?

49
Mask Operations

• Simple for Computers
• Computers have circuitry to AND to numbers
• Computers have circuitry to COMPARE two numbers
  to see if they are equal or not
• Very computer-friendly, so used on routers
• Difficult for people, unfortunately

50
Router Forwarding Tables

• Routers make forwarding decisions using router
  forwarding tables
• Generic format..
• Network or subnet
• Decision rule (deliver directly or pass on to a
  particular router) if Network or Subnet bits
  match those of IP destination address

51
Router Forwarding Tables
Refinement

• Note
• Book calls first column the IP address part
• More precisely, designates a particular network
  or subnet
• All packets to that network or subnet are
  forwarded in the same way

52
Router Forwarding Tables

• Router Compares Destination IP Address to Each
  Row in Router Forwarding Table
• If matches, delivers according to Delivery rule
• If destination address of IP packet is
  128.171.17.13, network and subnet bits
  (128.171.17) match, so router delivers packet
  locally (directly)

53
Router Forwarding Tables

• Also Has a Mask Column
• Tells number of network or networksubnet bits
• If Mask in a row is 24 bits long, router only
  compares first 24 bits of packets IP destination
  address to Net/Subnet bits in table row
• Tells size of network part or networksubnet parts

54
Router Forwarding Tables

• Also Has a Mask Column
• A network mask for a host outside the
  organizations network
• A subnet mask for an internal host
• Cant tell which by looking at the mask
• Dont worry. Its all automatic

55
Router Forwarding Tables

• Example
• Destination IP Address is 128.171.17.13
• Mask is 24, so only look at 128.171.17
• Matches rows network/subnet bits, so use Local
  (direct) delivery

56
Router Forwarding Tables

• Longest Match Principle
• Must select one row to determine delivery
• If two rows match, use longest match, that is
  match to greatest number of bits
• For 128.171.17.13, use local delivery (24-bit
  match)

57
Router Forwarding Tables

• Metric
• If same length of match, turn to metric column
• Metric describes the desirability of a choice
• If metric is cost, choose lowest cost
• For other metrics (speed, etc.), may chose
  largest value

58
Router Forwarding Tables

• There May be No Matches
• One IP Address Part is Always 0.0.0.0
• If there is no match, choose its next-hop router
  (called the Default Router)

59
Router Forwarding Tables

• Recap of Selection Rules
• Compare destination IP address of an arriving
  packet against ALL rows within the router
  forwarding table because there may be multiple
  matches
• Select a single row that matches
• If multiple rows match, select the longest match
• If multiple rows tie on the longest match, select
  the row with the largest or smallest metric,
  depending on the specific metric
• If there is no match, select the default router
  row

60
Router Forwarding Tables

• Delivery
• Table not only designates local delivery or a
  next hop router
• Also designates the router interface (port) that
  will be used for delivery

61
Dynamic Routing Protocols

• How Do Routers Get Information for their Router
  Forwarding Tables?
• Share router forwarding table information
• Standards for these exchanges are called dynamic
  routing protocols

Router Forwarding Table Information
62
Dynamic Routing Protocols

• How Do Routers Get Information for their Router
  Forwarding Tables?
• Thanks to dynamic routing protocols, the Internet
  needs no central point of control
• Routers create their router forwarding tables
  strictly by information from peers and their own
  knowledge

Router Forwarding Table Information
63
Internet Control Message Protocol (ICMP)
64
ICMP

• Internet Control Message Protocol
• IP is the delivery standard at the TCP/IP
  internet layer
• ICMP is the standard for supervisory messages
• IP and ICMP are designed to work together Even
  have adjacent RFC (standard) numbers
• ICMP message is carried in the information field
  of an IP packet

65
ICMP

• Several ICMP Message Types
• Error messages warn of problems
• Not error correction, because there is no
  transmission of lost or damaged packets

Error Message
66
ICMP

• Several ICMP Message Types
• ICMP query request message asks host if it is
  active
• Queried host sends back a query response message
• Also called Echo and Ping

Echo Request
Echo Response
67
ICMP

• Several ICMP Message Types
• Flow control Source quench ICMP message asks
  other side to slow down

Source Quench
68
Source Quench

• Weak form of flow control
• When host sending packets gets source quench, it
  slows down
• If another source quench message arrives, slows
  down even more
• If source quench messages stop, slowly increases
  speed

69
ICMP

• ICMP Implements Other Supervisory Messages
• We have only given a few important examples

70
Dynamic Routing Protocols

• Why Dynamic Routing Protocols?
• Each router acts independently, based on
  information in its router forwarding table
• Dynamic routing protocols allow routers to share
  information in their router forwarding tables

Router Forwarding Table Data
71
Routing Information Protocol (RIP)

• Routing Information protocol (RIP) is the
  simplest dynamic routing protocol
• Each router broadcasts its entire routing table
  frequently
• Broadcasting makes RIP unsuitable for large
  networks

Routing Table
72
Routing Information Protocol (RIP)

• RIP is the simplest dynamic routing protocol
• Broadcasts go to hosts as well as to routers
• RIP interrupts hosts frequently, slowing them
  down Unsuitable for large networks

Routing Table
73
Routing Information Protocol (RIP)

• RIP is Limited
• RIP routing table has a field to indicate the
  number of router hops to a distant host
• The RIP maximum is 15 hops
• Farther networks are ignored
• Unsuitable for very large networks

Hop
Hop
74
Routing Information Protocol

• Is a Distance Vector Protocol
• New York starts, announces itself with a RIP
  broadcast
• From this message, Chicago learns that New York
  is one hop away
• Passes this on in its broadcasts

NY is 1
New York
Chicago
Dallas
1 hop
75
Routing Information Protocol

• Learning Routing Information
• Dallas receives broadcast from Chicago
• Already knows Chicago is one hop from Dallas
• So New York must be two hops from Dallas
• Places this information in its routing table

NY is 1
New York
Chicago
Dallas
1 hop
1 hop
NY is 2
76
Routing Information Protocol

• Slow Convergence
• Convergence is getting correct routing tables
  after a failure in a router or link
• RIP converges very slowly
• May take minutes
• During that time, many packets may be lost

77
Routing Information Protocol

• Encapsulation
• Carried in data field of UDP datagram
• Port number is 520
• UDP is unreliable, so RIP messages do not always
  get through
• A single lost RIP message, however, does little
  or no harm

UDP Header
UDP Data Field RIP Message
78
OSPF Routing Protocol

• Link State Protocol
• Link is connection between two routers
• OSPF routing table stores more information about
  each link than just its hop count cost,
  reliability, etc.
• Allows OSPF routers to optimize routing based on
  these variables

Link
79
OSPF Routers

• Network is Divided into Areas
• Each area has a designated router

Area
Designated Router
80
OSPF Routers

• When a router senses a link state change
• Sends this information to the designated router

Area
Designated Router
Notice of Link State Change
81
OSPF Routers

• Designed Router Notifies all Routers
• Within its area

Area
Designated Router
Notice of Link State Change
82
OSPF Routers

• Efficient
• Only routers are informed (not hosts)
• Usually only updates are transmitted, not whole
  tables

Area
Designated Router
Notice of Link State Change
83
OSPF

• Fast Convergence
• When a failure occurs, a router transmits the
  notice to the designated router
• Designated router send the information back out
  to other routers immediately

84
OSPF

• Encapsulation
• Carried in data field of IP packet
• IP protocol field value is 89
• IP is unreliable, so OSPF messages do not always
  get through
• However, a single lost OSPF message usually does
  little or no harm

IP Header
IP Data Field OSPF Message
85
Selecting RIP or OSPF

• Within a network you control, it is your choice
• Your network is an autonomous system
• Select RIP or OSPF based on your needs
• Interior routing protocol

86
Selecting RIP or OSPF

• RIP is fine for small networks
• Easy to implement
• 15 hops is not a problem
• Broadcasting, interrupting hosts are not too
  important

87
Selecting RIP or OSPF

• OSPF is Scalable
• Works with networks of any size
• Management complexities are worth the cost in
  large networks

88
Border Gateway Protocol (BGP)

• To connect different autonomous systems
• Must standardized cross-system routing
  information exchanges
• BGP is most popular today
• Gateway is the old name for router
• Exterior routing protocol

Autonomous System
Autonomous System
BGP
89
Border Gateway Protocol (BGP)

• Distance vector approach
• Number of hops to a distant system is stored in
  the router forwarding table
• Normally only sends updates

Autonomous System
Autonomous System
BGP
90
Border Gateway Protocol (BGP)

• Encapsulation
• BGP uses TCP for delivery
• Reliable
• TCP is only for one-to-one connections
• If have several external routers, must establish
  a TCP and BGP connection to each

Autonomous System
Autonomous System
BGP
91
Internet Control Message Protocol (ICMP)
92
ICMP

• Internet Control Message Protocol
• IP is the delivery standard at the TCP/IP
  internet layer
• ICMP is the standard for supervisory messages
• IP and ICMP are designed to work together Even
  have adjacent RFC (standard) numbers
• ICMP message is carried in the information field
  of an IP packet

93
ICMP

• Several ICMP Message Types
• Error messages warn of problems
• Not error correction, because there is no
  transmission of lost or damaged packets

Error Message
94
ICMP

• Several ICMP Message Types
• ICMP query request message asks host if it is
  active
• Queried host sends back a query response message
• Also called Echo and Ping

Echo Request
Echo Response
95
ICMP

• Several ICMP Message Types
• Flow control Source quench ICMP message asks
  other side to slow down

Source Quench
96
Source Quench

• Weak form of flow control
• When host sending packets gets source quench, it
  slows down
• If another source quench message arrives, slows
  down even more
• If source quench messages stop, slowly increases
  speed

97
ICMP

• ICMP Implements Other Supervisory Messages
• We have only given a few important examples

98
Dynamic Routing Protocols

• Why Dynamic Routing Protocols?
• Each router acts independently, based on
  information in its router forwarding table
• Dynamic routing protocols allow routers to share
  information in their router forwarding tables

Router Forwarding Table Data
99
Routing Information Protocol (RIP)

• Routing Information protocol (RIP) is the
  simplest dynamic routing protocol
• Each router broadcasts its entire routing table
  frequently
• Broadcasting makes RIP unsuitable for large
  networks

Routing Table
100
Routing Information Protocol (RIP)

• RIP is the simplest dynamic routing protocol
• Broadcasts go to hosts as well as to routers
• RIP interrupts hosts frequently, slowing them
  down Unsuitable for large networks

Routing Table
101
Routing Information Protocol (RIP)

• RIP is Limited
• RIP routing table has a field to indicate the
  number of router hops to a distant host
• The RIP maximum is 15 hops
• Farther networks are ignored
• Unsuitable for very large networks

Hop
Hop
102
Routing Information Protocol

• Is a Distance Vector Protocol
• New York starts, announces itself with a RIP
  broadcast
• From this message, Chicago learns that New York
  is one hop away
• Passes this on in its broadcasts

NY is 1
New York
Chicago
Dallas
1 hop
103
Routing Information Protocol

• Learning Routing Information
• Dallas receives broadcast from Chicago
• Already knows Chicago is one hop from Dallas
• So New York must be two hops from Dallas
• Places this information in its routing table

NY is 1
New York
Chicago
Dallas
1 hop
1 hop
NY is 2
104
Routing Information Protocol

• Slow Convergence
• Convergence is getting correct routing tables
  after a failure in a router or link
• RIP converges very slowly
• May take minutes
• During that time, many packets may be lost

105
Routing Information Protocol

• Encapsulation
• Carried in data field of UDP datagram
• Port number is 520
• UDP is unreliable, so RIP messages do not always
  get through
• A single lost RIP message, however, does little
  or no harm

UDP Header
UDP Data Field RIP Message
106
OSPF Routing Protocol

• Link State Protocol
• Link is connection between two routers
• OSPF routing table stores more information about
  each link than just its hop count cost,
  reliability, etc.
• Allows OSPF routers to optimize routing based on
  these variables

Link
107
OSPF Routers

• Network is Divided into Areas
• Each area has a designated router

Area
Designated Router
108
OSPF Routers

• When a router senses a link state change
• Sends this information to the designated router

Area
Designated Router
Notice of Link State Change
109
OSPF Routers

• Designed Router Notifies all Routers
• Within its area

Area
Designated Router
Notice of Link State Change
110
OSPF Routers

• Efficient
• Only routers are informed (not hosts)
• Usually only updates are transmitted, not whole
  tables

Area
Designated Router
Notice of Link State Change
111
OSPF

• Fast Convergence
• When a failure occurs, a router transmits the
  notice to the designated router
• Designated router send the information back out
  to other routers immediately

112
OSPF

• Encapsulation
• Carried in data field of IP packet
• IP protocol field value is 89
• IP is unreliable, so OSPF messages do not always
  get through
• However, a single lost OSPF message usually does
  little or no harm

IP Header
IP Data Field OSPF Message
113
Selecting RIP or OSPF

• Within a network you control, it is your choice
• Your network is an autonomous system
• Select RIP or OSPF based on your needs
• Interior routing protocol

114
Selecting RIP or OSPF

• RIP is fine for small networks
• Easy to implement
• 15 hops is not a problem
• Broadcasting, interrupting hosts are not too
  important

115
Selecting RIP or OSPF

• OSPF is Scalable
• Works with networks of any size
• Management complexities are worth the cost in
  large networks

116
Border Gateway Protocol (BGP)

• To connect different autonomous systems
• Must standardized cross-system routing
  information exchanges
• BGP is most popular today
• Gateway is the old name for router
• Exterior routing protocol

Autonomous System
Autonomous System
BGP
117
Border Gateway Protocol (BGP)

• Distance vector approach
• Number of hops to a distant system is stored in
  the router forwarding table
• Normally only sends updates

Autonomous System
Autonomous System
BGP
118
Border Gateway Protocol (BGP)

• Encapsulation
• BGP uses TCP for delivery
• Reliable
• TCP is only for one-to-one connections
• If have several external routers, must establish
  a TCP and BGP connection to each

Autonomous System
Autonomous System
BGP
119
IP Version 6

• Current Version of IP is IP Version 4
• This is the version we have been discussing
• Has 32-bit IP address fields
• Not long enough running out of IP addresses
• Next Version will be IP Version 6
• Will have 128-bit IP address fields
• Will allow vast numbers of IP addresses (2128)
• Being adopted slowly

120
IPv6

• Current version of the Internet Protocol is
  Version 4 (v4)
• Earlier versions were not implemented
• The next version will be Version 6 (v6)
• No v5 was implemented
• Informally called IPng (Next Generation)
• IPv6 is Already Defined
• Continuing improvements in v4 may delay its
  adoption

121
IPv6

• IPv6 will raise the size of the internet address
  from 32 bits to 128 bits
• Now running out of IP addresses
• Will solve the problem
• But current work-arounds are delaying the need
  for IPv6 addresses

122
IPv6

• Improved Security
• But, through IPsec, v4 is being upgraded in
  security as well
• Improved Quality of Service (QoS)
• But under IETF Differentiated Services (diffserv)
  initiative, IPv4 is being upgraded in this area
  as well

123
IPv6

• Extension Headers
• IPv4 Headers are complex
• IPv6 basic header is simple
• Has extension headers for options

Basic Header
Extension Header 1
Extension Header 2
124
IPv6

• Extension Headers
• Basic header has 8-bit Next Header field
• Identifies first extension header or says that
  payload follows (256 possible)

Basic Header
NH
Extension Header 1
Extension Header 2
125
IPv6

• Extension Headers
• Each extension header also has 8-bit Next Header
  field
• Identifies next extension header or says that
  payload follows

Basic Header
Extension Header 1
NH
Extension Header 2
126
IPv6

• Extension Headers
• Next header field is an elegant way to allow
  options
• Easy to add new extension headers for new needs

Basic Header
Extension Header 1
NH
Extension Header 2
127
Terminology Confusion

• TCP/IP is a Standards Architecture
• Includes not only TCP and IP but also UDP, HTTP,
  and many other protocols
• May not even use TCP (UDP instead) or IP (ARP
  instead, as discussed in Module A)
• TCP and IP are Individual Standards
• Within the TCP/IP Architecture

128
More on PPP

• Point-to-Point Protocol

129
Data Link Layer Process

• Internet layer process passes EACH IP packet to
  the data link layer process for delivery over the
  data link

Internet LayerProcess
IP Packet
Data Link LayerProcess
130
PPP

• Point-to-Point Protocol
• Popular data link layer protocol for dial-in
  connections
• Supported by Microsoft Windows
• Between data link layer processes on user PC and
  first router
• Not between user PC and the destination host

PPP
DLL Process
DLL Process
User PC
First Router
131
PPP

• Negotiation Phase
• Before exchanging data frames, the two sides
• Negotiate conditions of PPP operation
• Also negotiate how specific protocols will be
  handled, such as IP
• Not limited to IP

PPP
DLL Process
DLL Process
User PC
First Router
132
PPP

• Data Frames
• Header
• Information field (IP packet or other
  information)
• Trailer with Frame Check Sequence field
• Error detection but not correction
• If an error is found, PPP frame is discarded

Trailer
Information Field
Header
IP Packet
133
PPP

• Flag Fields (1 Octet Each)
• Always contain 01111110
• Designates start of frame and end of frame
• No length field necessary

Flag
Addr
Ctrl
Prot
Info
CRC
Flag
134
PPP

• Address Field (1 Octet)
• PPP was designed to allow several devices at each
  end
• For modem-modem communication, only one device at
  each end
• Has fixed value 11111111

Flag
Addr
Ctrl
Prot
Info
CRC
Flag
135
PPP

• Control Field (1 Octet)
• PPP was designed to allow control information
• Not used in PPP included because PPP is based on
  an older protocol that used this field
• In PPP, the control field contains the fixed
  value 00000011

Flag
Addr
Ctrl
Prot
Info
CRC
Flag
136
PPP

• Protocol Field (2 Octets)
• Identifies the contents of the information field
• There are values for IP, IPX, other internet
  layer protocols that may be carried in the
  information field
• There are values for supervisory messages

Flag
Addr
Ctrl
Prot
Info
CRC
Flag
137
PPP

• Cyclical Redundancy Check (2 Octets)
• For error-checking information
• Allows receiver to detect a PPP frame with a
  transmission error
• Receiver discards such frames error detection
  but not reliability (no error correction)

Flag
Addr
Ctrl
Prot
Info
CRC
Flag
138
Physical Layer Process

• Data link layer process passes EACH data link
  layer frame to the physical layer process for
  delivery to the next computer (router or host)

Data Link LayerProcess
DL Frame
Physical LayerProcess
139
Physical Layer Process

• Physical layer process does not create a protocol
  data unit
• Sends one bit at a time over the data link
  connecting the sending computer to the next
  computer
• It is the data link layer process that organizes
  these bits into frames over the data link

Physical LayerProcess
Physical LayerProcess
10110
140
Key Point

141
Reliability

• Only TCP is Reliable or Needs to Be
• Corrects errors, gives application programs clean
  data
• Corrects errors that occur a the transport layer
  or lower layers because only correctly received
  TCP segments are acknowledged