Download Scaling the Network: The Internet Protocol Networking CS 3470, Section 1

Scaling the Network:
The Internet Protocol
Networking
CS 3470, Section 1
Network Layer: Introduction
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How does it all fit?
Data link layer
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Network layer
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Delivers frames between two
physically connected hosts
Delivery of packets from
machine to machine
Hop by hop between hosts and routers
Transport layer
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Between two end hosts
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Today
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Networking forwarding
Internet Protocol (IP)
IP Classful Address Scheme
ARP!
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Network Layer Functions
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Addressing
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Globally unique address for each routable device
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Assigned by network operator
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Need to map to MAC address
Forwarding
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Logical address, unlike MAC address
From input port to appropriate output port in a router
Routing
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Which path to use to forward packets from src to dest
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Network Layer Forwarding
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Forwarding input port to appropriate output
port in a router
We already talked about forwarding over the
network layer
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Datagram / Connectionless
Virtual Circuit Switching
Which one is used with IP?
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Datagram vs Virtual Circuit
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Datagram (example: IP)
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Data exchange among computers
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“Smart” end systems (computers)
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“Elastic” service, no strict timing req.
Can adapt, perform control, error recovery
Simple inside network, complexity at “edge”
Many link types
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Different characteristics
Uniform service difficult
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Datagram vs Virtual Circuit
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Virtual Circuit (Example: ATM)
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Evolved from telephony
Human conversation:
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Strict timing, reliability requirements
Need for guaranteed service
Quality of service
“Dumb” end systems
Complexity inside network
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Internetworking
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What is an internetwork?
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An arbitrary collection of networks interconnected to provide
some sort of host-host packet delivery service
IP
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IP stands for Internet Protocol
Key tool used today to build scalable,
heterogeneous internetworks
IP
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A IP router is a gateway from one network to
another
Can interface with many network types
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Ethernet
PPP
Token Ring
802.11
... more
[TCP/UDP]/IP
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Two well-known transport level protocols that
run on top of IP at the hosts are UDP and TCP
TCP
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Connection-based protocol
Error recovery
Packets arrive in order
UDP
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Connectionless protocol
No error recovery
Packets can arrive in any order, or not at all
Internetworking
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A simple internetwork showing the protocol
layers
IP connects them all!
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IP Service Model
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Packet Delivery Model
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Connectionless model for data delivery
Best-effort delivery (unreliable service)
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What bad stuff can happen?
Global Addressing Scheme
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Provides a way to identify all hosts in the network
Packet Format
IP Fragmentation and Reassembly
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Each network has some MTU (Maximum
Transmission Unit)
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Ethernet (1500 bytes), FDDI (4500 bytes)
Strategy
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Fragmentation occurs in a router when it receives a
datagram that it wants to forward over a network
which has (MTU < datagram)
Reassembly is done at the receiving host
All the fragments carry the same identifier in the
Ident field
Fragments are self-contained datagrams
IP does not recover from missing fragments
IP Fragmentation and Reassembly
IP datagrams traversing the sequence of physical networks
IP Fragmentation and Reassembly
Header fields used in IP fragmentation. (a) Unfragmented packet; (b) fragmented packets.
IP Addressing
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Globally unique logical address for a host
Address resolution
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Logical to physical address mapping
What was the physical address?
Is possible to address any host in the
network
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Even if on different physical network
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IP Addressing
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A 32-bit number that uniquely identifies a
location
Written using dotted decimal notation
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Common form: 134.161.240.211
Binary representation:
10000110 10100001 11110000 11010011
Two-level hierarchy: network id and host id
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Network IDs administered by Internet Assigned
Number Authority (IANA)
Host IDs administered locally
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IP Addressing
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IP address is assigned to each network
interface (NIC)
Routers connect two or more physical
networks
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Each interface has its own address
Multi-homed host
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A host having multiple connections to Internet
Multiple addresses identify the same host
Does not forward packets between its interfaces
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IP Addressing
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Classful addressing scheme separates groups of
addresses into classes
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Class A
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Class B
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8 bits used for network (256)
24 bits used for hosts and network devices (16,777,216)
Binary address starts with 0
16 bits for networks (65,536)
16 bits for hosts and network devices (65,536)
binary address starts with 10
Class C
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24 bits for the network (16,777,216)
8 bits for the host (256)
Binary address starts with 110
IP “Classful” Addressing Scheme
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Three unicast address classes: A, B, and C
One multicast: class D
class
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A
0 network
B
10
C
110
D
1110
1.0.0.0 to
127.255.255.255
host
network
128.0.0.0 to
191.255.255.255
host
network
multicast address
host
192.0.0.0 to
223.255.255.255
224.0.0.0 to
239.255.255.255
32 bits
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Address Resolution
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IP address is virtual
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Not understood by underlying physical networks
IP packets need to be transmitted by the
underlying physical network
Address resolution
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Translating IP address to physical address
Address Resolution Protocol (ARP)
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ARP
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A router has to know where to deliver
packets on the local network
ARP is used to discover MAC addresses
based on IP addresses
ARP Cache
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Each computer maintains a cache table
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IP address  hardware address mapping
Only about computers on the same network
Exchanges ARP messages
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To resolve IP addresses with unknown hardware
addresses
Encapsulated in Ethernet data frame
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ARP Protocol
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When a node sends an IP packet
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Look up destination address in the ARP table
If not found
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To another node on the same physical network
Broadcast a request to the local network
Whose IP address is this?
What info should the request message
contain?
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ARP Example
arp who-has 192.168.10.1 tell node31.ceee.lab
arp reply 192.168.10.1 is-at 00:60:08:ce:9d:3b
arp who-has node31.ceee.lab tell 192.168.10.254
arp reply node31.ceee.lab is-at 00:02:3f:b4:cd:87
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ARP Response
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The target node responds to sender (unicast?)
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On receiving the response
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Requester updates its table
Other nodes upon receiving the request
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With its physical address
Adds the requester into its ARP table (why?)
Refresh the requester entry if already there
No action otherwise (why?)
Table entries deleted if not refreshed for a while
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ARP Example
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ARP broadcast by W requesting hardware
address of Y
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