10/13/2015© 2008 raymond p. jefferis iiilect 07 1 internet protocol
TRANSCRIPT
04/19/23 © 2008 Raymond P. Jefferis III Lect 07 1
Internet Protocol
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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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Connectionless Functions
• Unicasting of datagramseach datagram routed from source to destination
• Multicasting of datagramssingle datagram routed to many destinations
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Internet Protocol (IP)
• A connectionless (datagram) service
• Supports connectionless transport (TCP)(TCP also supports connection-oriented
transport)
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Internet Protocol Routing
• Allows interconnection of subnetworks within a Local Area Network
• Allows interconnection of Local Area Networks
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Subnet Interconnection
Workstation
Workstation
Hub Router
Workstation
Workstation
Hub
Subnet Subnet
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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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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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LAN Interconnection
Workstation
Workstation
Hub Router
Workstation
Workstation
Hub
Network 1 Network 2
OtherSubnets
Router
OtherSubnets
Router
OtherNetworks
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Larger Networks
• Wide Area Networks (WANs)
• May operate with different protocols
• Gateway couples these
• Internet is an example
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WAN Interconnection
Workstation
Workstation
Hub Router
Workstation
Workstation
Hub
Network 1 Network 2
OtherSubnets
Router
OtherSubnets
Router
Gateway
Internet
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Effect on Application Data
• TCP adds header at transport layer
• IP adds header at network layer
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TCP/IP Header Embedding
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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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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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MAC Address Format
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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 addressHost addresses may be subnetted
• left bits are Subnet
• rightmost bits are Host
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Network Address Classes
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Example
• Widener University - Class B address147.31.xxx.yyy
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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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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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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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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: N.N.S.H
• subnet mask is: 255.255.255.0
– Example: 510 hosts (H) in subnet (S)• IP address is: N.N.S-H.H
• subnet mask is: 255.255.254.0
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Subnet Calculators
• Simplify binary subnet calculations
• Are available free on the Internet
• Search on “subnet calculator”
• Example:– http://www.subnet-calculator.com/
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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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Address Translation
• IP to HardwareAddress Resolution Protocol (ARP)
• Hardware to IPReverse Address Resolution Protocol (RARP)
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ARP/RARP Overview
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ARP Request Packet
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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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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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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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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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IP Header
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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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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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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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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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ICMP
• Internet Control Message Protocol
• Conveys return error messages to source from an IP network
• No retransmission if lost
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ICMP Header Format
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Some ICMP Types & CodesTYPE CODE DESCRIPTION
0 Echo reply3 Destination unreachable3 0 Network unreachable3 1 Host unreachable3 2 Protocol unavailable3 3 Port unreachable3 4 Fragmentation needed4 Source quench5 Redirect
11 Time exceeded11 0 Time to live exceeded15 Information request16 Information reply
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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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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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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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RIP2 (RIP) Header
Note: White area repeats for each router addressed.
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RIP Commands
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
COMMAND DESCRIPTION
1 Request
2 Response
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RIP Version NumberVERSION DESCRIPTION
0 Ignore datagram1 Check 0-fields2 Newly defined fields
>2 Ignore 0-fields
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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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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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Weighted Digraph Representation
• Vertices– routers– networks
• Edges– paths
• to routers
• to networks
– corresponding costs
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OSPF Packet Format
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OSPF Fields
• Version Number• at present, always 1
• Packet Type• 1 = Hello
• 2 = Database Description
• 3 = Link State Request
• 4 = Link State Update
• 5 = Link State Acknowledgment
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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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Link State Tables
• Destination ID
• Next Hop ID
• Distance Metric– delay– data rate– unit cost ($)– combination
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Network Routing Diagram
N9 N5
N3
Router
R13 1
7
5
4
1
Router
R2
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SPF Routing Table for R2
Destination Next Hop Metric
N3 N3 1
N5 N5 4
R1 R1 7
N9 N5 4