Untitled

10/30/00

Internet Protocol

- Layering used with TCP/IP




	-This layering represents the internet more closer than the ISO-7 layer model
	-Physical layer
		- Basic network hardware
	-Network interface
		-Media Access (MAC)
			format and addressing
	-Internet layer
		- Facilities to send packets across the internet using multiple routers
	-Transport layer
		- Transport of data from one application to another
	- Application
		-User program



- Layering Principles
	Software implementing layer N at the destination receives exactly the message sent by software implementing layers N at the source.



Internet Protocol IP


-Layer 3
-Defines
	- Internet addressing
	- Packet format
	- Routing
-IP addressing
	-32 bits long
	  	-> 2³²=2¹²M=2²K M ~ 4 Billion addresses
	- Independent of hardware addressing
	- An abstraction	
	- Unique value for each host
	- One IPAddress belongs only to one host
	- Some host(routers) can have more than one IPaddress  because they could be connected to others

Important
	An IP address identifies a connection between a computer and a network.  A computer with multiple network connections(e.g.. routers) must be assigned one IP address for each connection
	
	
	


e.g.. CISCO 1 is main router in lab
> host CISCO 1
	All IP addresses of CISCO 1
	
>ypcat host -> gives all IP addresses used in CS department
	e.g.. ypcat host | grep CISCO 1 -> all IP addresses of CISCO 1
	
	e.g.. ypcat host | grep 128.10.3.x -> gives all IP address in net 128.10.3
	
	e.g.. ypcat passwd - all users

IP Address


-Divided into 2 parts
	- Prefix identifies network
	- Suffix identifies the host
- A global authority assigning a unique prefix for a network
- A local administrator assigns a unique suffix for a host







Classes of Address

11/01/00
Dotted Decimal Notation


- Shorthand for IP address
- Each octet is represented in decimal and separated by dots

- Each digit is in the range from 0-255
Important
	THIS IS NOT THE SAME AS DNS NAMES LIKE mentor.cc.purdue.edu
	DNS=Domain Name Service
	


129.52.6.0 -> class ?   (129 = 1000 0001)
           -> class B
		   		Net number 129.52.0.0(Put zeros in host # spaces) 
				Host # 6.0
128.0.2.3 -> class B
				Net number 128.10.0.0
				Host # 2.3
192.5.48.3 -> class c    (192 = 1100 0000)
				Net number 192.5.48   
				Host # 3
10.2.0.32 -> class A      (10 = 0000 1010)
				Net number 10.0.0.0
				Host # 2.0.32

Class A -> Large Network
Class B -> Medium Network
Class C -> Small Network

For each Class we can represent the NET portion as 1's and Host portion as 0's.  This is called "Network Mask"

Class		network Mask 
    A						255.0.0.0 
    B						255.255.0.0
    C						255.255.255.0
	

Network # = IPAddr & Network Mask
      & = bitwise and
e.g.. 10.2.0.32 & 255.0.0.0 = 10.0.0.0


Special IPAddresses

All 0's All 0's this host Boot strapping(IP Addr is not available)
Net # All 0's network number When you refer to a net
Net # All 1's Directed Broadcast (Broadcast in this network)
e.g 129.10.255.255
Progs that use broadcast
>rusers -users in every machine in the local network. (Routers usually have the options turned off)(Applications that need broadcast)
All 1's All 1's Broadcast in all attached networks (Limited Broadcast) 
127(first byte) Any ex. 127.0.0.1 Loopback The same computer (all the time)


 
 
 
 
 


IP Packets
-IP runs on heterogeneous networks
-A router that connects two networks with different king of hardware can not copy the packet as it is and place it in the other network.


-IP Packets were created to run on basically ANY kind of network hardware
-A router will copy the IP packet and place it in a new hardware frame when routing.  The old frame is discarded
-There is a RFC for almost every network hardware that tells you how to implement IP on that hardware.
ex: IP on Ethernet, token ring, serial line, ATM

11/3/00

IP Packets

20 Bytes(fixed IP hdr) Vers - 4 HLen - Header length Serv-Priority (IPSRC) ID and Offset, and last "fragmentation bit" - Fragmentation and reassembly -Max length of IP packet = 64K bytes -Max Ethernet packet = 1500 bytes -MTU -> Maximum Transfer Unit eth MTU=1500 bytes -IP packets may need to be fragmented if the packet is larger than the MTU

-Routers may need to fragment IP packets -ID and Offset are used for reassembly -Reassembly is done at the destination. This is because packets may follow different paths and it would be impossible to reassembly in the routers. - Time to Live - # of secs packet has been in the internet(including routers) -Max is 255 seconds - After 255 secs packet is discarded - By default, a router will decrement the TTL field by one when the packet is routed - This prevents that a packet may circulate forever due to a routing loop - ID needs to be recycled after 64K packets. The TTL sets a limit when an old ID is still valid. - Type - protocol used on TCP of IP, TCP, UDP, ICMP - Hdr Checksum - Header Checksum - Src and Dest IP - Src and dest - IP options - optional - recording route - Data - is just data

IP Routing Internet - Hosts,Networks, Routers Routers - A piece of hardware that performs IP routing - Computer with specialiezed software - UNIX BSD(Berkely Standard Distribution) includes a program called "Routed" that can be run to use a host as a router. The host needs to have more than one network interface to connect two networks. "Routed" was substituted by "gated" ... www.gated.com


All 0's	All 0's	this host	Boot strapping(IP Addr is not available)
Net #	All 0's	network number	When you refer to a net
Net #	All 1's	Directed Broadcast (Broadcast in this network) e.g 129.10.255.255 Progs that use broadcast >rusers -users in every machine in the local network.	(Routers usually have the options turned off)(Applications that need broadcast)
All 1's	All 1's	Broadcast in all attached networks (Limited Broadcast)
127(first byte)	Any	ex. 127.0.0.1 Loopback	The same computer (all the time)