You have seen how the TCP/IP protocol suite is used to allow communication between different networks.
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TCP/IP (Transmission Control Protocol/Internet Protocol) was developed to allow communication between different types of computers and networks.

The features incorporated in the design produced a very reliable protocol suite that became widely used in other organisations.

TCP/IP was first implemented on ARPAnet which eventually became the Internet.

The TCP/IP protocol stack maps closely to the layers of the OSI model.

The Internet Protocol (IP) provides connectionless best-effort delivery routing of packets.

Delivery of these packets is not guaranteed, nor are they guaranteed to arrive in the sequence in which they were sent.

The Internet Control Message Protocol (ICMP) is used to send error and control messages between hosts and gateways.

The Address Resolution Protocol (ARP) is used to map an IP address to a physical address.

The Reverse Address Resolution Protocol (RARP) maps physical or MAC addresses to IP addresses.

The Transmission Control Protocol (TCP) is a connection-oriented transport layer protocol that provides reliable full-duplex data transmission.

TCP guarantees packet delivery and data integrity.

It also initiates handshaking, controls packet sequencing, flow control, and handles errors.

The User Datagram Protocol (UDP) is a simple protocol that exchanges packets without acknowledgements or guaranteed delivery.

It is used in situations where the reliability of TCP is not needed, for example, with protocols such as SNMP.

Both UDP and TCP use port or socket numbers to pass information to the upper layers of the protocol stack.

The File Transfer Protocol (FTP) provides a way to move files between computer systems.

Trivial File Transfer Protocol (TFTP) is a simplified version of FTP used by routers.

The Network File System (NFS) Protocol, is a distributed file system that allows remote file access across a network.

The protocol that provides electronic mail with a transport mechanism is the Simple Mail Transfer Protocol (SMTP).

The Telnet protocol allows logins to remote systems, and is used by routers to connect to other routers.

The rlogin command is similar to Telnet.

The Simple Network Management Protocol (SNMP) enables administrators to monitor a network from a single workstation.

It enables routers to return information about their routing tables.
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You have seen how IP addresses are assigned and host names resolved in a TCP/IP environment.
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Each IP address uniquely identifies a host within an internetwork.

Part of an IP address identifies a particular network, part identifies a subnetwork if present, and part identifies a specific host.

An IP address is a 32-bit address which consists of two parts, the network part and the host part.

An IP address must be unique on the internetwork.

IP addressing supports five different network classes, the most common of which are classes A, B, and C.

The most significant bit pattern determines the class of the address, as well as how many bits make up the network portion of the address.

Class A addresses are used for very large networks. The first bit in a class A address is set to 0. Class A network numbers range from 1.0.0.0 to 126.0.0.0.

Class B addresses always have the first two address bits set to 10. Class B network numbers range from 128.1.0.0 to 191.254.0.0.

The first three bits in a class C address are 110. Class C network numbers range from 192.0.1.0 to 223.255.254.0.

Class D addresses are used for multicast packets. They lie in the range 224 to 239 decimal, and begin with the binary digits 1110.

Class E addresses are reserved for future additions to the IP addressing scheme, and are in the range 240 to 255. The first four bits in a class E address
are 1111.

Sometimes host names are used instead of addresses. These names must be translated to the Internet or IP address before the data can be delivered.

Host tables and network tables are used to resolve frequently used host names to IP addresses on small networks.

Large networks such as the Internet use the Domain Name System (DNS) to resolve host names.
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You have seen how subnets and subnet masks are created and planned.
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Subnets allow you to utilize addressing space more efficiently.

Subnetting involves using part of the node component of an IP address to act as an additional network address.

Subnet masking is a technique you can use to adapt IP addresses to subnets.

Routing decisions are then based on network and subnet numbers.

A subnet mask is a 32-bit number that you apply to an IP address to override the default network/node address division.

Subnet masks indicate which of the bits in the host field are used to specify the subnets in a particular network.

You assign a value of 1 to each bit in the subnet mask that corresponds to a part of the IP address that refers to the network rather than the node.

Class A, B, and C addresses all have default subnet masks that reflect their default network/node address divisions.

There is a trade-off between the number of available subnet addresses and the number of hosts that can be supported on each subnet.

The number of possible subnets you can have depends on the number of bits allocated to the subnet address.

The number of hosts per subnet is obtained from the number of unmasked bits (0s) in the subnet mask.

The RFC 1219 system allows for changes to the subnet mask without reassigning existing IP addresses.
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You have seen how IP addresses are configured on a router interface.
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A new Cisco router can obtain an initial IP address and configuration file if another router, a BOOTP server, or a DNS server exist on the network.

When none of these exist on the network, you can configure the router manually using the System Configuration Dialog.

The System Configuration Dialog guides you
through the steps necessary to create an
initial configuration file.
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You have learned about using hierarchical addressing and variable length subnet masks.
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A scalable routing protocol should 

^B«»^b be able to handle address limitations

^B«»^b support hierarchical topology

IP routers make decisions based on hierarchical addressing.

A prefix identifies a block of host numbers and is used for routing to that block.

Address classes, subnet masks, and length
indications are used to identify important
contiguous bits in a prefix.

Classful routers only accept certain prefix lengths while classless routers accept any prefix length.

Variable length subnet masking (VLSM) involves masking already existing subnets.

VLSM reduces the number of IP addresses required in networks.

VLSM subnets should be grouped to enable consolidation of routing information.

Classless routing supports VLSM because it includes a prefix length indication with its address.
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