Basic fundamental concepts in Inter-networking...

1. INTERNETWORKING
Why : Interconnect External World for Effective Communication
Goal : Make an Communication system
 Seamless, Uniform, General-purpose
 Universal, Hides heterogeneity from user
Heterogeneity Is Inevitable : No single networking technology
best for all needs
Let’s look at how to build an internet from ground up…
By,
Mahendhira kumar.C
3rd ECE-A
JSRGI
INTERCONNECT+NETWORK’s

2. 2
TCP/IP Layers
• Layer 1: Physical
– Basic network hardware
• Layer 2: Network Interface(N2N)
– MAC frame format
– MAC addressing
– Interface between computer and network
• Layer 3: Internet
– Facilities to send packets across
internet composed of multiple routers
• Layer 4: Transport(P2P)
– Transport from an application on one
computer to application on another
• Layer 5: Application(User)
– Everything else
Messages (UDP) or
Streams (TCP)
Application
Transport
Internet
UDP or TCP packets
IP datagrams
Network-specific frame
Message
Layers
Underlying network
Network interface
Howis it possible to send bits across incompatible
LANs and WANs?
Solution: protocol software running on each host and router
smooth's out differences between different networks
Implements an internet protocol (i.e., set of rules) that
governs how hosts and routers should cooperate when
they transfer data from network to network.
TCP/IP is protocol (family) for global IP Internet
Note: TCP/IP layering model replaces the old ISO model

3. • Typically, packet starts in its LAN. Gateway receives it (broadcast
on LAN to “unknown” destination).
• Gateway sends packet to gateway on the destination network
using its routing table. If it can use the packet’s native protocol,
sends packet directly. Otherwise, tunnels it.
 What happens when large packet
wants to travel through network
with smaller maximum packet
size? Fragmentation(MTU <
datagram)
 HOW :
• Gateways break packets into
fragments; each sent as
separate packet.
• Gateway on the other side have
to reassemble fragments into
original packet.
How internet Works?
Problem’s In internet
Ethernet :1500 Bytes,
FDDI: 4500 Bytes,
PPP : 512 Bytes.

4. Transparent Fragmentation
Non-Transparent Fragmentation
2 kinds of fragmentation
 Small-packet network transparent to
other subsequent networks.
 Fragments of a packet addressed to
the same exit gateway, where packet
is reassembled.
 All fragments to go through same
gateway
 Only reassemble at destination host.
 Each fragment becomes a separate
packet.
 Thus routed independently.
 Problems : Hosts must reassemble.
Every fragment must carry header
until it reaches destination host.

5. Internet as Collection of Sub-networks

6. Internet Protocol -Kahn-Cerf
What is IP (Glue)
• IP stands for Internet Protocol
• Key tool used today to build scalable, heterogeneous internetworks
IP addresses
• Configured, or learned dynamically
• Like a postal mailing address
• Hierarchical name space of 32 bits (e.g., 12.178.66.9)
• Not portable, and depends on where the host is attached
• Used to get a packet to destination IP subnet.
• Another way of thinking of this is that it is unreliable
Work Flow
• Transport layer breaks data streams into datagrams; fragments
transmitted over Internet, possibly being fragmented.
• When all packet fragments arrive at destination, reassembled by network
layer and delivered to transport layer at destination host.
dataIP address of destinationIP address of source
header
up to 64 kilobytes
 IP address identifies the host computer.
 Port number identifies a running
process in the host computer

7. IP (Internet Protocol) : “Network" layer protocol (H2H) for addressing
Connection-less(Un-Reliable)
TCP (Transmission Control Protocol) : Transport layer (P2P)
Connection-oriented (Reliable)
UDP (User Datagram Protocol) : Transport layer (P2P)
Connection-less(Un-Reliable)
Faster than TCP
Con’d (Internet Protocol)
UDP carries the port numbers of
source and destination, and an
optional checksum, in addition
 Telnet
 Serial Line Internet Protocol (SLIP)
 Point-to-Point Protocol (PPP)
 Simple Mail Transport Protocol (SMTP)
 Simple Network Management Protocol (SNMP)
 File Transfer Protocol (FTP)
 Routing Information Protocol (RIP)
Other Similar Protocol’s :

8. Packet Delivery Model (Datagram Delivery)
 Connectionless model for data delivery
 Best-effort delivery (unreliable service)
• packets are lost
• packets are delivered out of order
• duplicate copies of a packet are delivered
• packets can be delayed for a long time

9. Packet Format(IPv6)Packet Format(IPv4)
 Version (4): currently 4
 Hlen (4): number of 32-bit words in
header
 TOS (8): type of service (not widely
used)
 Length (16): number of bytes in this
datagram
 Ident (16): used by fragmentation
 Flags/Offset (16): used by
fragmentation
 TTL (8): number of hops this
datagram has traveled
 Protocol (8): demux key (TCP=6,
UDP=17)
 Checksum (16): of the header only
 DestAddr & SrcAddr (32)
Source address
(128 bits)
Destination address
(128 bits)
Version (4 bits) Traffic class (8 bits) Flow label (20 bits)
Payload length (16 bits) Hop limit (8 bits)Next header (8 bits)
IPv4 : 2^32 ~ 4M-Addresses
IP addresses:128 bits (16 bytes)
IPv6 : 2^128 Addresses
IP addresses:32 bits (4 bytes)
Migration from IPv4
 backward compatibility: IPv6
addresses include IPv4 addresses
 Islands of IPv6 networks, traffic
tunnels though other IPv4 networks

10. IP ADDRESSES
 IP address formats.
10
 4 Billion IP address: Half are A type, ¼ is B type, and 1/8 is C type.
 Type’s: IPv4: Current, predominant version (32-bit long)
IPv6( IPng): Evolution of IPv4 (16-byte long)
Unused -

11. IPClassification
• Class A: 128 networks with 16M hosts each.
• Class B: 16,384 networks with 65K hosts each.
• Class C: 2M networks with 256 hosts each.
More than 500K networks connected to the Internet.
Network numbers centrally administered by ICANN.
• Class D: Class D is reserved for multicast addresses
• Class E: It is reserved for future use as a Class E IP address.
Problem: A single A, B, or C address refers to a single
network.
As organizations grow, what happens?

12. 12
Solution=>Sub-netting
• Sub-netting: Add another level to address/routing hierarchy : subnet
• Divide the organization’s (A, B, and C) address space into multiple
“subnets”.
• How? Use part of the host number bits as the “subnet number”.
• Example: Consider a university with 35 departments.
• With a class B IP address, use 6-bit subnet number and 10-bit
host number.
• This allows for up to 64 subnets
each with 1024 hosts.
• For Increases routing efficiency

13. TunnelingSub-netMask
A B
IPv6 IPv6
IPv6 encapsulated in IPv4 packets
Encapsulators
IPv4 network

14.  Transition away from address classes
–Enables more conservative allocation of IP addresses
 CIDR notation
– Specify network through combination of
IP + Routing prefix(/n)
– (/n) number of leftmost contiguous bits to be used for the
network mask
 Example: 69.166.48.43/23 IP address Routing prefix
Classless Inter-Domain Routing (CIDR)

15. Problem: We need to send message to some IP address, but don’t know
what MAC address to send to
ARP : Protocol to query machines on a network for the correct MAC
address
 Broadcasts “Who has IP address: 1.2.3.4”???
 1.2.3.4 should respond “MAC address 00:11:22:33:44:55, for
1.2.3.4”
 So that, System can now correctly address the link layer frame
Security Issue: Attacker can send ARP reply's with wrong address to
“hijack” network traffic!
1=Request
2=Reply
= IPv4
Address Resolution Protocol (ARP)

16.  Defines a collection of error messages that are sent back to the source host
whenever a router or host is unable to process an IP datagram successfully.
 Protocol to support Network diagnosis/Error reporting/Simple queries
 Can identify sender when an error message occurs:
Internet Control Message Protocol (ICMP)
Packet Format

17. Question : How do hosts get an IP address, net-mask, routing when they first
join a network?
DHCP :
 DHCP server is responsible for providing configuration information to
hosts.
 There is at least one DHCP server for an administrative domain
Protocol :
 Discovery – client sends broadcast UDP packet asking for an address
lease
 Offer – server will offer a lease for an address
 Request – client a sends acknowledgement that they want to accept the
offer
 Acknowledgement – includes lease configuration information and
duration
Dynamic Host Configuration Protocol (DHCP)

18. IEEE No. Name Title Reference
802.3 Ethernet CSMA/CD Networks (Ethernet) [IEEE 1985a]
802.4 Token Bus Networks [IEEE 1985b]
802.5 Token Ring Networks [IEEE 1985c]
802.6 Metropolitan Area Networks [IEEE 1994]
802.11 WiFi Wireless Local Area Networks [IEEE 1999]
802.15.1 Bluetooth Wireless Personal Area Networks [IEEE 2002]
802.15.4 ZigBee Wireless Sensor Networks [IEEE 2003]
802.16 WiMAX Wireless Metropolitan Area Networks[IEEE 2004a]
IEEE Version’s

19. Quiz’s
 For a CIDR address of the form W.X.Y.Z/20, what is the maximum
number of hosts possible in the network?
 Segment it with 5 possible Segments with starting address 22,050. When
9000 bytes are transferred?
 What is the subnet address if the destination IP address is 144.16.34.124
and the subnet mask is 255.255.240.0?
 For an IP address 10.17.5.122 and subnet mask 255.255.128.0, what is
the subnet address? How many hosts per subnet are possible?
 For the subnet mask 255.255.192.0, how many hosts per subnet are
possible?
 Which of the following can be the starting address of a CIDR block that
contains 512 addresses?
144.16.24.128 144.16.75.0
144.16.24.0 144.16.0.0
 Using simple subnets, is it possible to divide a network into unequal sized
subnets?

20. THANK YOU FOR YOUR ATTENTION…
Questions
...

21. 21
Example: A Sending a Packet to B
How does host A send an IP packet to host B?
A
R
B
A sends packet to R, and R sends packet to B.

22. 22
Host A Decides to Send Through R
• Host A constructs an IP packet to send to B
– Source 111.111.111.111, destination 222.222.222.222
• Host A has a gateway router R
– Used to reach destinations outside of 111.111.111.0/24
– Address 111.111.111.110 for R learned via DHCP
A
R
B

23. 23
Host A Sends Packet Through R
• Host A learns the MAC address of R’s interface
– ARP request: broadcast request for 111.111.111.110
– ARP response: R responds with E6-E9-00-17-BB-4B
• Host A encapsulates the packet and sends to R
A
R
B

24. 24
R Decides how to Forward Packet
• Router R’s adaptor receives the packet
– R extracts the IP packet from the Ethernet frame
– R sees the IP packet is destined to 222.222.222.222
• Router R consults its forwarding table
– Packet matches 222.222.222.0/24 via other adaptor
A
R
B

25. 25
R Sends Packet to B
• Router R’s learns the MAC address of host B
– ARP request: broadcast request for 222.222.222.222
– ARP response: B responds with 49-BD-D2-C7-56-2A
• Router R encapsulates the packet and sends to B
A
R
B