CCNA - Revision history

Admin: /* The Internet Layer Protocols */

2010-08-03T19:07:12Z

The Internet Layer Protocols

← Older revision		Revision as of 22:07, 3 August 2010
Line 939:		Line 939:

	It isn't a protocol as it's more of a service run by routers on the behalf of other devices ( usually PC machines ). It causes a lot of traffic and cause larger ARP tables but the advantage is that in case the gateway ( router ) goes down a machine on a subnet can reach remote subnets without routing ( or even a gateway ).		It isn't a protocol as it's more of a service run by routers on the behalf of other devices ( usually PC machines ). It causes a lot of traffic and cause larger ARP tables but the advantage is that in case the gateway ( router ) goes down a machine on a subnet can reach remote subnets without routing ( or even a gateway ).

			==IP Addressing==

			An IP address is a numeric identifier assigned to each machine on a network specifying its specific location in the network.

			Unlink the hardware address (MAC) which is hardcoded into the network interface card ( NIC ), the IP address is a software address ( logical address ). It was designed to allow a host on one network to be able to communicate to a host in a different network regardless of the type of LANs the hosts are in.

			===IP Terminology===

			A few stuff you should know before continuing:

			'''Bit''' - one digit .. either 1 or a 0

			'''Byte''' - 7 or 8 bits ( depending if the parity is used )

			'''Octet''' - 8 bits. Just an ordinary 8 bit binary number

			'''Network Address''' - The actual IP address used in routing to send packets to a remote network, like: 172.16.0.0 ; 10.0.0.0 ; 192.168.10.0

			'''Broadcast Address''' - Is an address used by applications and hosts to send information to all nodes on a network. Examples would be: 255.255.255.255 -> all networks, all nodes ; 172.16.255.255 -> all subnets on network 172.16.0.0 ; 10.255.255.255 -> all subnets on network 10.0.0.0

			===IP Addressing Scheme===

			An IP address consists of 32 bit of information divided into 4 sections ( octets ), each containing 1 byte - 8 bits. It is usually displayed as:

			* A Dotted decimal: 172.16.30.56

			* Binary : 10101100.00010000.00011110.00111000

			* Hexadecimal: AC.10.1E.38 - isn't used as often when IP addressing is discussed but is used by Windows in programs like Registry

			An IP address is a hierarchical address. The hierarchical addressing structures is a two- or three-level structure, structured by network and host or by network, subnet and host.

			===Network Addressing===

			A network address uniquely identifies a netowork. Every machine on a network shares the same network number as a part of its IP address. In 172.16.30.56 for example 172.16 is a network address and 30.56 is the node address ( uniquely identifying a machine on this network ).

			Based on the network size there are some classes. Class A is for a small number of networks with large number of nodes. Class C is reserved for a big number of networks with a small number of nodes. Class B is just in between !

			To ensure efficient routing the leading bits of an address are the important ones ( a router can speed up the routing by just reading the first bit ).

			[[File:Classes_of_networks.png]]

			====Network Address Range: Class A====

			A class A of network addresses always has the first bit set to 0 ( like this: 0xxxxxxx ) -> values between 0 and 127.

			'''0'''0000000 = 0<br/>
			'''0'''1111111 = 127

			====Network Address Range: Class B====

			A class B network always starts with the first bit set to 1 and the second to 0 ( like : 10xxxxxx ) -> values between 128 and 191

			'''10'''000000 = 128
			'''10'''111111 = 191

			====Network Address Range: Class C====

			A class C network always starts with the first two bits set to one and the 3rd to 0 ( like 110xxxxx ) -> values between 192 and 223

			'''110'''00000 = 192
			'''110'''11111 = 223

			====Network Addresses Ranges: Class D and E====

			Classes between 224 and 255 are reserved for D ( 224-239 - multicast ) and E ( 239-255 - scientific purposes ) networks.

			====Network Addresses Ranges: Special Purpose====

			Network address of all 0s - this network or segment

			Network address of all 1s - All networks

			Network 127.0.0.1 - loopback test. Local node can send itself a packet without generating network traffic.

			Node Address of all 0s - network address - any host on the network

			Node Address of all 1s - all nodes in a network

			Entire IP of 0s (0.0.0.0) - any network - default route

			Entire IP of 1s (255.255.255.255) - broadcast to all nodes on network

	==Subnetting==		==Subnetting==

Admin: /* The Internet Layer Protocols */

2010-08-03T16:37:59Z

The Internet Layer Protocols

Admin: /* Port Numbers */

2010-08-03T16:36:48Z

Port Numbers

← Older revision		Revision as of 19:36, 3 August 2010
Line 845:		Line 845:
	'''Data''' - Data from the upper layer		'''Data''' - Data from the upper layer

	===Port Numbers===		==Port Numbers==

	[[File:Port_numbers.png]]		[[File:Port_numbers.png]]

Admin: /* The Internet Layer Protocols */

2010-08-03T13:05:37Z

The Internet Layer Protocols

Admin: /* Port Numbers */

2010-08-03T13:04:32Z

Port Numbers

← Older revision		Revision as of 16:04, 3 August 2010
Line 845:		Line 845:
	'''Data''' - Data from the upper layer		'''Data''' - Data from the upper layer

	====Port Numbers====		===Port Numbers===

	[[File:Port_numbers.png]]		[[File:Port_numbers.png]]

Admin: /* The Internet Layer Protocols */

2010-08-03T13:02:28Z

The Internet Layer Protocols

← Older revision		Revision as of 16:02, 3 August 2010
Line 864:		Line 864:

	* Proxy ARP		* Proxy ARP

			=====Internet Protocol (IP)=====

			All the other protocols exist because of IP. It is essentially the Internet Layer.

			What it does it check each packet's address, then using a routing table decides where the packet should go next ( choosing the best path ) ( the lower layer - Network Access - doesn't know about these things, it only handles physical link ( local network)).

			Identifying devices on networks require a logical ( or software ) address ( which simplifies a lot the routing ) and a hardware address.

			IP gets the segments from the Host-to-Host layer fragmenting them into a data stream ( packets ) and then reassembles them back into segments on the receiving side. Each packet contains the IP address of the sender and receiver so each router ( layer 3 ) device makes routing decisions based on these info.

			[[File:Ip_header.png]]


			'''Version''' - IP version number ( 4 is most used now )

			'''Header Length''' - in 32-bit words

			'''Priority and Type of Service''' - the first 3 bits are the priority bits, the rest tell how the datagram should be handled

			'''Total Length''' - packet length including header and data

			'''Identification''' - Unique IP-packet value

			'''Flags''' - specifies if fragmentation should occur

			'''Fragment offset''' - it allows fragmentation and reassembly if the packet is too large for a frame. Also allows different maximum transmission units(MTUs)

			'''Time to Live''' - used to stop IP packets from continuously circle the network looking for a home. It is the number of "hops" a packet is allowed to pass to get to a home, if it doesn't 'till the TTL expires - it's gone

			'''Protocol''' - port of the upper-layer protocol. TCP has port 0x06, UDP has 0x17, ICMP 0x01, IP in IP(tunneling) 0x04, IGRP 0x09, EIGRP 0x88, OSPF 0x89, IPv6 0x41, GRE 0x47, Layer 2 TUNNEL L2TP 0x115 ( Complete list at [www.iana.org/assignments/protocol-numbers protocol numbers] ). It supports other Network Protocols like ARP/ICMP.

			'''Header checksum''' - CRC for header only

			'''Source IP address''' - 32-bit IP address of the sending station

			'''Destination IP address''' - 32-bit IP address of the destination station

			'''Options''' - used for network testing, debugging, security and more.

			'''Data''' - the actual data given from the upper-layers

			=====Internet Control Message Protocol (ICMP)=====

			An ICMP packet has the following characteristics:

			* It can provide hosts with information about network problems

			* It is encapsulated with IP datagrams

			The following are the most common events that an ICMP packet relates to:

			Destination Unreachable - is sent back to the sender if a router can't sent a datagram any further.

			Buffer Full - is sent while a router's buffer memory for receiving datagram is full

			Hops - because each IP datagram is allowed only a certain number of routers to pass through ( called hops ), if it reaches this hop limit before arriving at its destination, the last router to receive the datagram deletes it then it informs the sender of the deletion of the datagram

			2 of the most used programs that use this protocol are:

			Ping - Packet Internet Groper - uses ICMP to check the connectivity of machines in a network ( both logical and physical )

			Traceroute - using ICMP packets, discovers the path of a packet as it traverses a network to its destination

			=====Address Resolution Protocol (ARP)=====

			It's what gets the hardware address of a host when having the logical (IP) address. It does this like this: when the IP has something to send, the Network Access Layer needs to know the hardware address ( if it doesn't have it in cache already ). If it doesn't have it in cache it'll send a broadcast asking for the hardware address of the specified IP address.

			=====Reverse Address Resolution Protocol (RARP)=====

			It's the exact reverse of the ARP. It is used to find the IP address of a hardware address. Usually used by diskless machine who don't have an IP address first.

			=====Proxy Address Resolution Protocol (Proxy ARP)=====

			It isn't a protocol as it's more of a service run by routers on the behalf of other devices ( usually PC machines ). It causes a lot of traffic and cause larger ARP tables but the advantage is that in case the gateway ( router ) goes down a machine on a subnet can reach remote subnets without routing ( or even a gateway ).

	==Subnetting==		==Subnetting==

Admin: /* DoD Model */

2010-08-03T11:11:04Z

DoD Model

← Older revision		Revision as of 14:11, 3 August 2010
Line 701:		Line 701:
	* Internet Layer -> Network layer		* Internet Layer -> Network layer

	It designates the protocols relating to the logical transmission of packets over the entire network. It's taking care of hosts addressing giving them IP ( Internet Protocol ) addresses and routing of packets among multiple networks.		It designates the protocols relating to the logical transmission of packets over the entire network. It's taking care of hosts addressing giving them IP ( Internet Protocol ) addresses and routing of packets among multiple networks. None of the upper-layers have any functions related to routing.

	* Network Access Layer -> Data Link / Physical Layer		* Network Access Layer -> Data Link / Physical Layer

Admin: /* The Internet Layer Protocols */

2010-08-03T11:09:10Z

The Internet Layer Protocols

← Older revision		Revision as of 14:09, 3 August 2010
Line 854:		Line 854:

	====The Internet Layer Protocols====		====The Internet Layer Protocols====

			* Internet Protocol (IP)

			* Internet Control Message Protocol ( ICMP )

			* Address Resolution Protocol ( ARP )

			* Reverse Address Resolution Protocol ( RARP )

			* Proxy ARP

	==Subnetting==		==Subnetting==

Admin: /* Host-to-Host Layer Protocols */

2010-08-02T16:08:42Z

Host-to-Host Layer Protocols

← Older revision		Revision as of 19:08, 2 August 2010
Line 844:		Line 844:

	'''Data''' - Data from the upper layer		'''Data''' - Data from the upper layer

			====Port Numbers====

			[[File:Port_numbers.png]]

			Both UDP and TCP use port numbers to differentiate the conversations across the network. Source ports are randomly assigned by the sending host and are over 1024 to set up sessions. Numbers lower than 1024 are reserved by IANA for well-known ports. The (source) port numbers are different to differentiate the sessions. TCP and the upper-layers don't use hardware or logical addressing to understand the sending host's address like the Data Link or Network layers do.

			A ''syn'' packet is sent to the destination service telling the remote destination that the source station wants to create a session. The reply usually will be an accept message.

			====The Internet Layer Protocols====

	==Subnetting==		==Subnetting==

Admin: /* Transmission Control Protocol (TCP) */

2010-08-02T15:10:48Z

Transmission Control Protocol (TCP)

← Older revision		Revision as of 18:10, 2 August 2010
Line 765:		Line 765:
	====Transmission Control Protocol (TCP)====		====Transmission Control Protocol (TCP)====

	* ~~Connection Orientated~~		* Sequenced

	* Reliable		* Reliable

	* ~~Error checking~~		* Connection-orientated

	* ~~- Overhead~~		* Virtual Circuit

			* Acknowledgements

			* Windowing flow control

	TCP takes large blocks of information from an application and breaks them into segments. It applies sequences and numbers them so the destination TCP stack can put the information back in the order the application inteded. TCP waits for an acknowledgement from the receiving end so it can retransmit those that aren't acknowledged.		TCP takes large blocks of information from an application and breaks them into segments. It applies sequences and numbers them so the destination TCP stack can put the information back in the order the application inteded. TCP waits for an acknowledgement from the receiving end so it can retransmit those that aren't acknowledged.
Line 783:		Line 787:
	[[File:Tcp_segment_format.png]]		[[File:Tcp_segment_format.png]]

	The TCP header is 20 bytes long ( or up to 24 with options ). Here's a description of each field in the TCP segment:		The TCP header is 20 bytes long ( or up to 24 with options ... alot of overhead ). Here's a description of each field in the TCP segment:

	'''Source port''' - the port number (of the application sending the data) on the host sending the data		'''Source port''' - the port number (of the application sending the data) on the host sending the data

← Older revision		Revision as of 19:37, 3 August 2010
Line 853:		Line 853:
	A ''syn'' packet is sent to the destination service telling the remote destination that the source station wants to create a session. The reply usually will be an accept message.		A ''syn'' packet is sent to the destination service telling the remote destination that the source station wants to create a session. The reply usually will be an accept message.

	===The Internet Layer Protocols===		==The Internet Layer Protocols==

	* Internet Protocol (IP)		* Internet Protocol (IP)
Line 865:		Line 865:
	* Proxy ARP		* Proxy ARP

	====Internet Protocol (IP)====		===Internet Protocol (IP)===

	All the other protocols exist because of IP. It is essentially the Internet Layer.		All the other protocols exist because of IP. It is essentially the Internet Layer.
Line 906:		Line 906:
	'''Data''' - the actual data given from the upper-layers		'''Data''' - the actual data given from the upper-layers

	====Internet Control Message Protocol (ICMP)====		===Internet Control Message Protocol (ICMP)===

	An ICMP packet has the following characteristics:		An ICMP packet has the following characteristics:
Line 928:		Line 928:
	Traceroute - using ICMP packets, discovers the path of a packet as it traverses a network to its destination		Traceroute - using ICMP packets, discovers the path of a packet as it traverses a network to its destination

	====Address Resolution Protocol (ARP)====		===Address Resolution Protocol (ARP)===

	It's what gets the hardware address of a host when having the logical (IP) address. It does this like this: when the IP has something to send, the Network Access Layer needs to know the hardware address ( if it doesn't have it in cache already ). If it doesn't have it in cache it'll send a broadcast asking for the hardware address of the specified IP address.		It's what gets the hardware address of a host when having the logical (IP) address. It does this like this: when the IP has something to send, the Network Access Layer needs to know the hardware address ( if it doesn't have it in cache already ). If it doesn't have it in cache it'll send a broadcast asking for the hardware address of the specified IP address.

	====Reverse Address Resolution Protocol (RARP)====		===Reverse Address Resolution Protocol (RARP)===

	It's the exact reverse of the ARP. It is used to find the IP address of a hardware address. Usually used by diskless machine who don't have an IP address first.		It's the exact reverse of the ARP. It is used to find the IP address of a hardware address. Usually used by diskless machine who don't have an IP address first.

	====Proxy Address Resolution Protocol (Proxy ARP)====		===Proxy Address Resolution Protocol (Proxy ARP)===

	It isn't a protocol as it's more of a service run by routers on the behalf of other devices ( usually PC machines ). It causes a lot of traffic and cause larger ARP tables but the advantage is that in case the gateway ( router ) goes down a machine on a subnet can reach remote subnets without routing ( or even a gateway ).		It isn't a protocol as it's more of a service run by routers on the behalf of other devices ( usually PC machines ). It causes a lot of traffic and cause larger ARP tables but the advantage is that in case the gateway ( router ) goes down a machine on a subnet can reach remote subnets without routing ( or even a gateway ).

← Older revision		Revision as of 16:05, 3 August 2010
Line 853:		Line 853:
	A ''syn'' packet is sent to the destination service telling the remote destination that the source station wants to create a session. The reply usually will be an accept message.		A ''syn'' packet is sent to the destination service telling the remote destination that the source station wants to create a session. The reply usually will be an accept message.

	====The Internet Layer Protocols====		===The Internet Layer Protocols===

	* Internet Protocol (IP)		* Internet Protocol (IP)
Line 865:		Line 865:
	* Proxy ARP		* Proxy ARP

	=====Internet Protocol (IP)=====		====Internet Protocol (IP)====

	All the other protocols exist because of IP. It is essentially the Internet Layer.		All the other protocols exist because of IP. It is essentially the Internet Layer.
Line 906:		Line 906:
	'''Data''' - the actual data given from the upper-layers		'''Data''' - the actual data given from the upper-layers

	=====Internet Control Message Protocol (ICMP)=====		====Internet Control Message Protocol (ICMP)====

	An ICMP packet has the following characteristics:		An ICMP packet has the following characteristics:
Line 928:		Line 928:
	Traceroute - using ICMP packets, discovers the path of a packet as it traverses a network to its destination		Traceroute - using ICMP packets, discovers the path of a packet as it traverses a network to its destination

	=====Address Resolution Protocol (ARP)=====		====Address Resolution Protocol (ARP)====

	It's what gets the hardware address of a host when having the logical (IP) address. It does this like this: when the IP has something to send, the Network Access Layer needs to know the hardware address ( if it doesn't have it in cache already ). If it doesn't have it in cache it'll send a broadcast asking for the hardware address of the specified IP address.		It's what gets the hardware address of a host when having the logical (IP) address. It does this like this: when the IP has something to send, the Network Access Layer needs to know the hardware address ( if it doesn't have it in cache already ). If it doesn't have it in cache it'll send a broadcast asking for the hardware address of the specified IP address.

	=====Reverse Address Resolution Protocol (RARP)=====		====Reverse Address Resolution Protocol (RARP)====

	It's the exact reverse of the ARP. It is used to find the IP address of a hardware address. Usually used by diskless machine who don't have an IP address first.		It's the exact reverse of the ARP. It is used to find the IP address of a hardware address. Usually used by diskless machine who don't have an IP address first.

	=====Proxy Address Resolution Protocol (Proxy ARP)=====		====Proxy Address Resolution Protocol (Proxy ARP)====

	It isn't a protocol as it's more of a service run by routers on the behalf of other devices ( usually PC machines ). It causes a lot of traffic and cause larger ARP tables but the advantage is that in case the gateway ( router ) goes down a machine on a subnet can reach remote subnets without routing ( or even a gateway ).		It isn't a protocol as it's more of a service run by routers on the behalf of other devices ( usually PC machines ). It causes a lot of traffic and cause larger ARP tables but the advantage is that in case the gateway ( router ) goes down a machine on a subnet can reach remote subnets without routing ( or even a gateway ).