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Internet Protocol
5/25/2017
© 2009 Raymond P. Jefferis III
Lect 07 1
What is the Internet?
• A collection of separate networks
• Interconnected by routers and gateways
– routers interconnect similar networks
– gateways interconnect differing networks
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© 2009 Raymond P. Jefferis III
Lect 07 2
Connectionless Functions
• Unicasting of datagrams
each datagram routed from source to destination
• Multicasting of datagrams
single datagram routed to many destinations
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© 2009 Raymond P. Jefferis III
Lect 07 3
Internet Protocol (IP)
• A connectionless (datagram) service
• Supports connectionless transport (TCP)
(TCP also supports connection-oriented transport)
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© 2009 Raymond P. Jefferis III
Lect 07 4
Internet Protocol Routing
• Allows interconnection of subnetworks
within a Local Area Network
• Allows interconnection of Local Area
Networks
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© 2009 Raymond P. Jefferis III
Lect 07 5
Subnet Interconnection
Workstation
Workstation
Hub
Hub
Workstation
Workstation
Subnet
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Router
Subnet
© 2009 Raymond P. Jefferis III
Lect 07 6
Router
•
•
•
•
•
Interconnects subnets
Many ports, each on separate subnet
Operates at Network Layer
Restricts traffic - only subnet traffic visible
Can interconnect Local Area Networks
(LANs)
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© 2009 Raymond P. Jefferis III
Lect 07 7
Hub
•
•
•
•
Interconnects hosts on subnet
Many ports, all on same subnet
Operates at Data Link Layer
Does not restrict traffic (all traffic visible)
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© 2009 Raymond P. Jefferis III
Lect 07 8
LAN Interconnection
Other
Subnets
Other
Networks
Other
Subnets
Workstation
Workstation
Hub
Router
Router
Router
Workstation
Workstation
Network 1
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Hub
Network 2
© 2009 Raymond P. Jefferis III
Lect 07 9
Larger Networks
•
•
•
•
Wide Area Networks (WANs)
May operate with different protocols
Gateway couples these
Internet is an example
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© 2009 Raymond P. Jefferis III
Lect 07 10
WAN Interconnection
Internet
Gateway
Other
Subnets
Other
Subnets
Workstation
Workstation
Hub
Router
Router
Router
Workstation
Workstation
Network 1
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Hub
Network 2
© 2009 Raymond P. Jefferis III
Lect 07 11
Effect on Application Data
• TCP adds header at transport layer
• IP adds header at network layer
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© 2009 Raymond P. Jefferis III
Lect 07 12
TCP/IP Header Embedding
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© 2009 Raymond P. Jefferis III
Lect 07 13
Addressing of Network Nodes
• Physical address (Ethernet address)
– Medium Access Control (MAC) format
• 6 octets (uniquely assigned to hardware)
• Network address
– Internet Protocol (IP) format
• 4 octets (assigned by agency)
• Translation
– Address Resolution Protocol (ARP)
– Reverse Address Resolution Protocol (RARP)
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© 2009 Raymond P. Jefferis III
Lect 07 14
Physical (Hardware) Address
• MAC (Medium Access Control) address
• 6 octets (48 bits) Note: 248 = 2.8147x1014
– 3 octets of vendor code (Assigned by IEEE)
• 1 octet of flag bits
• 2 octets of vendor number
– 3 octets of serial number (Assigned by vendor)
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© 2009 Raymond P. Jefferis III
Lect 07 15
MAC Address Format
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© 2009 Raymond P. Jefferis III
Lect 07 16
Network (IP) Address
• 4 octets (32 bits) Note: 232 = 4.2950x109
• Left octet(s) are Network address
• leftmost bits signify address class
• next bits are network address
• Right octets are Host address
Host addresses may be subnetted
• left bits are Subnet
• rightmost bits are Host
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© 2009 Raymond P. Jefferis III
Lect 07 17
Network Address Classes
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Lect 07 18
Example
• Widener University - Class B address
147.31.xxx.yyy
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Lect 07 19
Addressing limits
• Class A (Super WAN - e.g. country)
– 27 networks, 224 hosts (3 octets)
• Class B (WAN/LAN)
– 214 networks, 216 hosts (2 octets)
• Class C (LAN)
– 221 networks, 28 hosts (1 octet)
(Note: all address octets can be 0 to 255 )
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© 2009 Raymond P. Jefferis III
Lect 07 20
Subnets
• Needed to make efficient use of addresses
• Reduce routing effort by assigning a single
address to all the subnets
• Resolve local traffic locally; keep Intra-net
traffic off the Inter-net
• Organize hosts into groups (LANs)
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© 2009 Raymond P. Jefferis III
Lect 07 21
Example Class B Subnet
Note that the Subnet divides the Host address space
Subnet mask will contain 1s in Subnet space;
0s in Host space
A 9-bit host space is assumed (510 hosts)
A 7-bit subnet space remains (126 subnets)
Note: Addresses 0 and 255 are reserved
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© 2009 Raymond P. Jefferis III
Lect 07 22
Subnet Masks
• Router will AND mask with IP address and
pass result through to local network
– Example: 254 hosts (H) in subnet (S)
• IP address is:
• subnet mask is:
N.N.S.H
255.255.255.0
– Example: 510 hosts (H) in subnet (S)
• IP address is:
• subnet mask is:
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N.N.S-H.H
255.255.254.0
© 2009 Raymond P. Jefferis III
Lect 07 23
Subnet Calculators
•
•
•
•
Simplify binary subnet calculations
Are available free on the Internet
Search on “subnet calculator”
Example:
– http://www.ccci.com/tools/subcalc/f1.html
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© 2009 Raymond P. Jefferis III
Lect 07 24
Host Mask Design Procedure
• Specify expected number of hosts (N)
–
–
–
–
all computers
printers
network devices (hubs, routers, etc.)
add 2 (for reserved 0 and 255 addresses)
• Set k to next power of 2 giving at least N
addresses
• Mask is 1s complement of 2k-1
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© 2009 Raymond P. Jefferis III
Lect 07 25
Address Translation
• IP to Hardware
Address Resolution Protocol (ARP)
• Hardware to IP
Reverse Address Resolution Protocol (RARP)
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© 2009 Raymond P. Jefferis III
Lect 07 26
ARP/RARP Overview
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© 2009 Raymond P. Jefferis III
Lect 07 27
ARP Request Packet
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Lect 07 28
Address Translation Procedure
• Source computer to send
• Outgoing packet is put in queue
• Special ARP request packet is broadcast on network
• Target computer responds
• Target computer returns packet with missing address
• Note: its “target” is original “source” computer
• Source computer sends queued packet
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© 2009 Raymond P. Jefferis III
Lect 07 29
147.31.232.120 To Send
Hardware Address Protocol Address
Source
00:20:af:c4:1d:2a
147.31.232.120
Destination
00:00:00:00:00:00
147.31.232.100
This packet will be broadcast to every host on
147.31.232.0 network (subnet)
Only 147.31.232.100 responds (unicast response)
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© 2009 Raymond P. Jefferis III
Lect 07 30
147.31.232.100 Answers
Hardware Address Protocol Address
Source
00:80:72:00:61:dc
147.31.232.100
Destination
00:20:af:c4:1d:2a
147.31.232.120
147.31.232.120 now has the hardware address it
needs to build packets to 147.31.232.100.
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© 2009 Raymond P. Jefferis III
Lect 07 31
Name Translation
• Name to IP-Address
(engr.widener.edu => 147.31.230.10)
• Domain Name Server (DNS)
– a hierarchy of database servers on the network
– local resolution attempted first; then network
– secondary (backup), usually available
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© 2009 Raymond P. Jefferis III
Lect 07 32
IP Header
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© 2009 Raymond P. Jefferis III
Lect 07 33
IP Header Fields
• Version (4 bits)
– version number
• Header Length (4 bits)
– in 32-bit words (5 is minimum)
• Type of Service (8 bits)
– Precedence (bits 0-2)
– Throughput (bit 4)
– Delay (bit 3)
– Reliability (bit 5)
– bits 6 & 7 reserved for future use
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© 2009 Raymond P. Jefferis III
Lect 07 34
IP Header Fields (Cont’d)
• Total length
– length of datagram, including header [bytes]
– design minimum: 576 bytes
• Identification
– sequence number for fragments
• Flags (3 bits)
– bit 0 = 0 (reserved) bit 2 = more fragments
– bit 1 = don’t fragment
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© 2009 Raymond P. Jefferis III
Lect 07 35
IP Header Fields (Cont’d)
• Fragment offset (13 bits)
– location of fragment in datagram (8-byte units)
• Time to live [seconds]
– each router must count down by one
• Protocol type
– for higher level processing of datagram
– (TCP = 6, UDP = 17)
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© 2009 Raymond P. Jefferis III
Lect 07 36
IP Header Fields (Cont’d)
• Source address (32 bits)
– IP address
• Destination address (32 bits)
– IP address
• Options
– all devices must implement
– typical: security, upper level protocols, etc.
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Lect 07 37
ICMP
• Internet Control Message Protocol
• Conveys return error messages to source
from an IP network
• No retransmission if lost
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© 2009 Raymond P. Jefferis III
Lect 07 38
ICMP Header Format
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© 2009 Raymond P. Jefferis III
Lect 07 39
Some ICMP Types & Codes
TYPE CODE
DESCRIPTION
0
Echo reply
3
Destination unreachable
3
0
Network unreachable
3
1
Host unreachable
3
2
Protocol unavailable
3
3
Port unreachable
3
4
Fragmentation needed
4
Source quench
5
Redirect
11
Time exceeded
11
0
Time to live exceeded
15
Information request
16
Information reply
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© 2009 Raymond P. Jefferis III
Lect 07 40
Some ICMP Interpretations
• Destination unreachable
(router can’t find route)
• Source quench
(reduce source rate)
• Time exceeded
(TTL decremented to zero by router)
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© 2009 Raymond P. Jefferis III
Lect 07 41
Routing Methods
• Distance Vector Protocol
(uses RIP - Routing Information Protocol)
Bellman-Ford routing algorithm
• Link State Protocol
(uses OSPF - Open Shortest Path First)
SPF routing algorithm (Dijkstra)
All routers know complete network
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© 2009 Raymond P. Jefferis III
Lect 07 42
RIP - Routing Information Protocol
• A distance vector protocol
• Uses hop count as metric (1 - 16)
• Peer routers exchange distance vectors
every 30 seconds
• Router considered off-line if timeout
exceeded (180 seconds)
• Problematic above subnet level
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© 2009 Raymond P. Jefferis III
Lect 07 43
RIP2 (RIP) Header
Note: White area repeats for each router addressed.
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Lect 07 44
RIP Commands
COMMAND
DESCRIPTION
1
Request
2
Response
Request:
For all or part of routing table of target
router (destination address - via next-hop)
Response:
All or part of routing table from target
router - or update
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© 2009 Raymond P. Jefferis III
Lect 07 45
RIP Version Number
VERSION
0
1
2
>2
5/25/2017
DESCRIPTION
Ignore datagram
Check 0-fields
Newly defined fields
Ignore 0-fields
© 2009 Raymond P. Jefferis III
Lect 07 46
OSPF - Open Shortest Path First
• An internal link state routing protocol
• Hierarchical routing by “areas”
• Link State Protocol (LSP) packets advertise
routes
• Routers can advertise 1-hop hosts as sets
• One router of broadcast LAN is
the“designated” router; failover to “backup”
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© 2009 Raymond P. Jefferis III
Lect 07 47
More OSPF Features
• Allows multiple route definitions
– by service types
– by costs
– by load (allows load balancing)
• Secures router databases
– all data exchanges authenticated
– only authenticated data can be propagated
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© 2009 Raymond P. Jefferis III
Lect 07 48
Weighted Digraph Representation
• Vertices
– routers
– networks
• Edges
– paths
• to routers
• to networks
– corresponding costs
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© 2009 Raymond P. Jefferis III
Lect 07 49
OSPF Packet Format
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Lect 07 50
OSPF Fields
• Version Number
• at present, always 1
• Packet Type
•
•
•
•
•
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1 = Hello
2 = Database Description
3 = Link State Request
4 = Link State Update
5 = Link State Acknowledgment
© 2009 Raymond P. Jefferis III
Lect 07 51
OSPF Fields (cont’d)
• Packet length, including header [bytes]
• Source router address (ID)
• Area ID
– Note: packets usually cover only 1 hop
• Checksum (1s complement)
• Authentication type
• Authentication field (64-bit)
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© 2009 Raymond P. Jefferis III
Lect 07 52
Link State Tables
• Destination ID
• Next Hop ID
• Distance Metric
–
–
–
–
delay
data rate
unit cost ($)
combination
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© 2009 Raymond P. Jefferis III
Lect 07 53
Network Routing Diagram
Router
N9
3
R1
1
N5
7
4
5
Router
R2
1
N3
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© 2009 Raymond P. Jefferis III
Lect 07 54
SPF Routing Table for R2
Destination
Next Hop
Metric
N3
N3
1
N5
N5
4
R1
R1
7
N9
N5
4
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© 2009 Raymond P. Jefferis III
Lect 07 55