Other Chapter Notes:

[Chapter One]

[Chapter Two]

[Chapter Three]

[Chapter Four]

[Chapter Five]

[Chapter Six]

[NID Outline]

[Back to Notes]

[Home]

IP Concepts

• Transmission Control Protocol/Internet Protocol (TCP/IP)
• Required to communicate between hosts on the internet
• TCP/IP is the standard for global communications between hosts and networks
• The TCP/IP Internet Model
• Layers (figure 1.1 on page 5)  
• OSI vs. TCP/IP and Data Types
• Application Layer
• Date type: Data Stream
• Handles implementation of user applications
• Software supports the implementation of the application (web browser and web server)
• Transport Layer
• Data type:  TCP segment
• Manages end-to-end communications between hosts
• Concerned with providing reliability over inherently unreliable layers
• Two transport layers
• TCP
• Ensures data delivery
• UDP (User Datagram Protocol)
• No promise of reliable delivery
• Network Layer
• Data type: IP datagram
• Gets data from source to destination
• Link Layer
• Data type: Ethernet frame
• Manages data transfer to and from physical medium
• Data Flow
• Data flows down TCP/IP stack of source computer and then it goes up the TCP/IP stack of the destination computer.
• Each layer talks to its “peer” layer, although the two computers do not directly interact with each other.
• Each layer adds it own leader and the receiving host reverses this by removing the header information.
• Process id repeated for each layer of the stack
• Packaging
• Bits, Bytes, and Packets
• Bit
• Binary
• Either a 0 or 1
• Byte
• Eight bits
• Large enough for an ASCII (American Standard Code for Information Interchange) character
• Multiple bytes are grouped together and sent over the network as a packet.
• A field know as the cyclical redundancy check (CRC), or checksum, is used to violate that the frame has not been damaged or corrupted in transit.
• IP packets need to include the sender and receiver addresses
• MAC Addresses
• Media Access Control
• 48 bits long
• Unique to each NIC
• Frame
• Frame header (14 bytes)
• Source and destination MAC addresses
• Frame data
• Trailer of 4 bytes that represent CRC
• Encapsulation revisited
• Layered packing configuration
• TCP header
• IP datagram
• Frame Header
• Ready to be sent
• First the data is gathered into the TCP segment and includes the TCP header and TCP data.
• If this was UDP, this would be a datagram.
• At the IP layer adds header information, then known as an IP datagram.
• The link layer adds another header and it is known as a frame.
• Process is repeated in reverse on the other computer.
• Interpretation of Layers
• Each protocol has its own layouts and formats.
• Refer to figure 1.5 on page 10 for IP header format.
• There are a set number of bits for each field.
• The protocol field lets you know which protocol is being used.
• Addresses
• Physical addresses, media access controller addresses
• MAC addresses will NOT be in the IP headers, MAC addresses mean nothing to IP.
• Physical MAC addresses are how the NIC interfaces with the network, and doesn’t know anything about IP addresses.
• Not uncommon to not know your IP address.
• Many times you are “loaned” an IP address for your session, either by an ISP or by DHCP (Dynamic Host Configuration Protocol).
• DHCP is good because it helps with the limit of available IP addresses.  By allowing an IP address to be used to a certain amount of time it can then use that address for another system instead of using two separate IP address.
• The Internet Address Number Authority (IANA) has set aside a block of IP addresses for internal addresses only.
• 192.168 and 176.12 subnets are to be used for hosts talking within a particular network.
• These should not leave the gateway.
• The ARP (Address Resolution Protocol) enables you to resolve the translation of physical MAC addresses to logical IP addresses.
• The source host broadcasts an ARP request, then the destination host picks it up and replies with its MAC address.
• During this, the source, destination, and all other listening hosts save this information.
• This saving cuts down on the number of ARP requests.
• Length is 48 bits, future plans are to expand that 128 bits.
• Logical Addresses, IP Addresses
• IP address is a 32 bit number.
• Classes
• Class A
• First 8 bits for network
• Last 24 bits for hosts
• More than 16 million possible hosts (2²⁴-1)
• 32 Bits for IP Address Space

•  
• Classes A, B, and C are unicast, when you send a packet; presumably you are addressing a single machine.
• Class D is multicast
• Class E is reserved for experimental use.
• Address Classes and IP Ranges

• Subnet Masks
• The masks informs a computer how many bits in its IP address have been relegated to the network and how many to the host.
• Service Ports
• TCP and UDP have 16-bit port number fields in their respective header fields.
• This means you can have up to 65,536 different ports.
• Most processes have an assigned port number, but there is nothing stopping you from changing that number to one of your choosing.
• Any service can run at any port.
• IP Protocols
• Two different transport models
• Connection-oriented model (TCP)
• Software ensures that the communication is reliable and complete and begins the process establishing a handshake connection.
• Ensures that all data sent is received.
• Reliable because each packet is acknowledged when it is received.  If a packet is not received, it is resent.
• Connectionless model (UDP)
• Send and pray delivery.
• No handshake and no promise of delivery.
• Just assemble packets and fire them into the network.
• Application must ignore the missing pieces or ask for them.
•  
• TCP is slower than UDP because of all the checking, but because of that it is a lot more reliable than UDP.
• ICMP (Internet Control Message Protocol)
• Ping
• Determine if a given network host is reachable.
• More information in Chapter 4.  
• IP Header Table
• Domain Name System
• A.k.a DNS
• DNS is a distributed database because the entire address table is not stored on a single host.
• Distributed across many servers.
• Translates a domain name to an IP address so you can go to that server.
• Routing: How you get there from here
• TCP/IP network layer is concerned with routing and how to get from one host to another.
• Layer where IP addresses are used.
• ARP is used to get an IP address from a MAC address so a packet can be sent.
• When the destination host is not on the local network, the traffic is sent to a default router.
• That router is responsible for sending the packet one hop closer to its destination.
• Routers maintain tables of routes that they know about. They use dynamic routing protocols to update their tables.
• Routing Protocols:
• Interior Gateway Protocols (IGPs)
• Routing traffic within a network that is under the same administration, also known as Autonomous System (AS).
• Routing Information Protocol (RIP)
• Open Shortest Path First (OSPF)
• Exterior Gateway Protocols (EGPs)
• Required when packets must travel between different Autonomous Systems.
• Border Gateway Protocol (BGP)is a widely used EGP.
• Currently provides routing protocol that supports the internet backbone.
• BGP servers must maintain routing table that include all of the external addresses on the internet.  
• TCP Header Table
• Ethernet Frame Header