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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