OSI Model - All People Seem To Need Data Processing
7 Application
6 Presentation
5 Session
4 Tranport
3 Network
2 Data Link
1 Physical
Layer 2 - switches - communicates using MAC addresses
Protocols such as Ethernet that operate at layer 2 do not see beyond
the local network.
The Internet layer, also often called layer 3 or the network layer, describes a global and configurable software addressing scheme that allows devices to communicate when they reside on remote network segments. The main protocol that operates at layer 3 is IP, and the network device that reads data at this layer is a router. Routers block broadcasts by default.
IPv6 uses 128-bit addresses instead of the 32-bit addresses used with IPv4, and, as a result, it can define many more addresses. Because few Internet routers are IPv6- compatible, IPv6 today is used over the Internet with the help of tunneling protocols. However, IPv6 is supported natively in Windows Vista, Windows 7, Windows Server 2008, and Windows Server 2008 R2.
TCP communication is two-way and reliable.
Many network services (such as DNS) rely on UDP instead of TCP as a transport protocol. UDP enables fast transport of datagrams by eliminating the reliability features of TCP, such as acknowledgments, delivery guarantees, and sequence verification. Unlike TCP, UDP is a connectionless service that provides only best-effort delivery to network hosts. A source host that needs reliable communication must use either TCP or a program that provides its own sequencing and acknowledgment services.
Network Map shows a map of all devices connected to the LAN. It relies on two components:
■ The Link Layer Topology Discovery (LLTD) Mapper component queries the network for devices to include in the map.
■ The LLTD Responder component responds to the queries from the Mapper I/O. Although these two components are included only in Windows Vista, Windows 7, Windows Server 2008, and Windows Server 2008 R2, you can install an LLTD Responder component on computers running Windows XP so that they will appear on a Network Map on other computers.
To open Network connection from a command line type ncpa.cpl
The three types of network components that can be bound to a connection:
■ Network Clients In Windows, network clients are software components, such as Client For Microsoft Networks, that allow the local computer to connect with a particular network operating system. By default, Client For Microsoft Networks is the only network client bound to all local area connections. Client For Microsoft Networks allows Windows client computers to connect to shared resources on other Windows computers.
■ Network Services Network services are software components that provide additional features for network connections. File And Printer Sharing For Microsoft Networks and QoS Packet Scheduler are the two network services bound to all local area connections by default. File And Printer Sharing For Microsoft Networks allows the local computer to share folders for network access. QoS Packet Scheduler provides network traffic control, including rate-of-flow and prioritization services.
■ Network Protocols Computers can communicate through a connection only by using network protocols bound to that connection. By default, four network protocols are installed and bound to every network connection: IPv4, IPv6, the Link-Layer Topology Discovery (LLTD) Mapper, and the LLTD Responder.
When you enable network bridging on a connection, all points entering the server (wireless, Token Ring, and Ethernet) appear on the same network. Hence, they can all share the wireless connection and get out to the Internet.
If you also want to define a default gateway along with the IPv4 configuration, you can add that information to the end of the command. For example, to configure the same IPv4 address for the local area connection with a default gateway of 192.168.33.1, type the following: netsh interface ipv4 set address “local area connection” static 192.168.33.5 255.255.255.0 192.168.33.1
To configure the Local Area Connection to obtain an address automatically, type the following:
netsh interface ipv4 set address "Local Area Connection" dhcp
Ping, Tracert, and Pathping utilities all rely on a layer 3 messaging protocol named Internet Control Message Protocol (ICMP).
ICMP is blocked by default by Windows Firewall, and it is also blocked by some routers and stand-alone firewalls. Consequently, to use Ping, Tracert, and PathPing successfully, you need to ensure that ICMP is not blocked by the remote host. To enable a firewall exception for ICMP on a computer running Windows Server 2008 R2, use Windows Firewall with Advanced Security console to enable the File and Printer Sharing (Echo Request – ICMPv4-In) firewall rule. To enable a firewall exception for ICMPv6, enable the File and Printer Sharing (Echo Request – ICMPv6-In) firewall rule. You can also enable these firewall rules throughout the domain by using Group Policy.
PathPing is similar to Tracert except that PathPing is intended to find links that are causing intermittent data loss. PathPing sends packets to each router on the way to a final destination over a period of time and then computes the percentage of packets returned from each hop.
arp converts an IP address to MAC address
arp -a displays arp cache
arp -d deletes arp cache
To resolve IP-to-MAC address mappings, IPv6 uses a protocol named Neighbor Discovery (ND) instead of the ARP protocol used by IPv4. For this reason, a nice benefit of an all- IPv6 network is that it prevents the possibility of Arp cache poisoning.
Note also that the same connection has been assigned a link-local IPv6 address beginning with fe80::.
This address is the IPv6 equivalent of an APIPA address.
ipv4 addresses are 32 bit and are divided between the network and host ID's
Each ipv4 address is 4 octet of 8 bits each
The subnet mask is used to determine which part of a 32-bit IPv4 address should be considered its network ID. For example, when you write 192.168.23.245/24, the /24 represents the subnet mask and indicates that the first 24 of the 32 bits in that IPv4 address should be considered its network ID. For the IPv4 address 131.107.16.200 shown in Figure 1-29 earlier, the first 16 bits according to the picture are used for the network ID. Therefore, the appropriate subnet mask to be used by a host assigned that address is /16.
So far, the discussion has focused on subnet masks in slash notation—also known as Classless Inter Domain Routing (CIDR) notation or network prefix notation. Slash notation is a common way of referring to subnet masks both on the 70-642 exam and in the real world. However, subnet masks are represented just as commonly in 32-bit dotted-decimal notation. In dotted-decimal notation, the subnet mask takes the form of a 32-bit IPv4 address. For example, the subnet mask /16 is represented in dotted-decimal notation as 255.255.0.0, and the subnet mask /24 is represented in dotted-decimal notation as 255.255.255.0.
When converting decimal to binary go left to right
200 = 11001000 128+64+0+0+8+0+0+0
Remember these essential points about routing and default gateways:
■ A default gateway must share the same network ID and be located within the same broadcast domain as the hosts it is serving.
■ If a host has no default gateway setting configured, that host will be unable to connect to the Internet or to any computers beyond broadcast range. For example, a private internal server that occasionally needs to download content from the Internet needs to have a default gateway configured.
■ Leaving the default gateway setting unconfigured on a host prevents access to that host from all points beyond the local subnet. In certain situations, therefore, you might in fact want to leave the default gateway setting unconfigured for security reasons.
An address block is the complete group of contiguous IP addresses that shares any single network ID. For example, an organization may purchase from an ISP a /24 address block with network ID 206.73.118. The range of addresses associated with this address block is 206.73.118.0–206.73.118.255.It is essential to understand that the addresses within an address block constitute a single network, and unless the network is subnetted—a possibility we will consider later in this lesson—that address block will serve a single broadcast domain with a single router, or way out of the network. The default gateway is the address assigned to that router within the same broadcast domain. Stated another way, an address block by default is designed to serve a single subnet.
A subnet is a group of hosts within a single broadcast domain that share the same network ID and the same default gateway address.
/x = The subnet mask
Block size = number of addresses
The maximum host capacity of an address block is always two fewer than the number of addresses in that network.
21 = 2
22 = 4
23 = 8
24 = 16
25 = 32
26 = 64
27 = 128
28 = 256
29 = 512
210 = 1024
211 = 2048
212 = 4096
Shortcut to calculate the number of addresses for a network:
2^(32–n) = number of addresses
For example, a /27 network includes 2^(32 – 27) = 2^5 = 32 addresses.
If the subnet mask value provided is 255.255.255.0 or greater, the calculation is fortunately very easy. Just use the following formula, where z is the value of the last octet: 256 – z = number of addresses
For example, if a network has a subnet mask of 255.255.255.240, the block size is 256 – 240 = 16 addresses. If a network has a subnet mask of 255.255.255.192, the block size is 256 – 192 = 64 addresses. If a network has a subnet mask of 255.255.255.0, the block size is 256 – 0 = 256 addresses. Remember that the block size will always be a power of 2, so if you have the powers of 2 memorized, you should be able to perform the calculation in your head. If the subnet mask value for a network is between 255.255.0.0 and 255.255.255.0, the calculation is still fairly easy. Just use the following formula, where y is the value of the third octet: (256 – y) * 256 = number of addresses
For example, if a network has a subnet mask of 255.255.252.0, the block size is (256 – 252) * 256 = 4 * 256 = 1024 addresses. If a network has a subnet mask of 255.255.240.0, the block size is (256 – 240) * 256 = 16 * 256 = 4096 addresses. Again, the block size will always be a power of 2, so if you have the powers of 2 memorized, you might still be able to perform the calculation in your head.
Network administrators rarely need to determine the address block size for a network with a subnet mask between 255.0.0.0 and 255.255.0.0, and you will not need to perform such a calculation on the 70-642 exam. However, for completeness, the formula is presented here (where x is the value of the second octet):
(256 – x) * 256 * 256 = number of addresses
For example, if you are designing a new network with 30 computers, you need 30 + 2, or 32, addresses for the subnet. Because 2^5 = 32, the value 32 is the smallest power of 2 that is big enough to accommodate your needs. 256 – 32 = 224, so you need a subnet mask of 255.255.255.224 to accommodate your new network. If p ≥ 256, set the first two octets to 255 and the fourth octet to 0. Then determine the following value and place it in the third octet: 256 – (p / 256).
The easiest way to subnet a network is to use one new and extended subnet mask on all computers within your internal address space. Doing so generates a number of subnets of equal size. When you subnet your network in this way, you can determine how many logical subnets have been created by using the formula 2^(n2– n1) = number of subnets where n2 is the length (in bits) of the new network ID used internally within the organization, and n1 is the length of the original network ID assigned externally to refer to the entire address block. For example, if you subnet a 10.0.100.0 /24 address space by using a /27 subnet mask on all hosts in your internal network, you generate 2^(27–24) = 2^3 = 8 subnets. Each of these 8 subnets includes 2^(32–27) = 2^5 = 32 addresses.
Variable Length Subnet Masks - When different subnets use different subnet masks depending on needed amount of addresses
To determine whether IP addresses are on the same subnet, first ensure that the hosts you are comparing have the same subnet mask configured. Then, compare the network IDs of the addresses. For /8, /16, and /24 subnet masks, this comparison is easy: simply compare the IP address values of the first, the first two, or the first three octets, respectively. If and only if the values are identical, the computers are configured on the same subnet. For example, the addresses 192.168.5.1 /24, 192.168.5.32 /24, and 192.168.5.64 /24 are all on the same subnet because they all share the network ID 192.168.5. For subnet masks of /25 and higher, divide the value of the last octet in each address by the address block size, and drop any remainder so that you are left with a whole number such as 0, 1, or 2. If and only if the resulting whole numbers are the same, the addresses are on the same subnet. For example, 192.168.5.1 /26 and 192.168.5.32 /26 are on the same subnet because the block size of a /26 network is 64, and if you discount the remainder, both 1 ÷ 64 and 32 ÷ 64 equal zero. However, 192.168.5.64 is on a different subnet because 64 ÷ 64 = 1. For subnet masks between /16 and /24, first convert the subnet mask to dotted-decimal notation by using a reference chart or by memorization. Subtract the value of the third octet in the subnet mask from 256, and then divide the value of the third octet in the IP addresses you want to compare by this resulting difference, dropping any remainders. If and only if the resulting values are the same, the addresses are on the same subnet. For example, if you want to compare 10.0.40.100 /21 and 10.0.41.1 /21, first determine that the dotted-decimal equivalent of /21 is 255.255.248.0, and then subtract 248 from 256 to obtain a value of 8. Finally, because 40 ÷ 8 = 5 and 41 ÷ 8 = 5 with some remainder, the two addresses are located on he same subnet.
Calculating the number of subnets
Calculate the bits in the subnet mask and default mask for the class of the ip. then calculate 2^x power where x is the number of bits that are 0 in default mask but 1 in subnet mask
ex 172.20.0.0
default mask 255.255.0.0 11111111 11111111 00000000 00000000
subnet mask 255.255.255.0 11111111 11111111 11111111 00000000
2^8 = 256
Calculating the number of hosts
Calculate the bits in the subnet mask and default mask for the class of the ip. then calculate 2^x power -2 where x is the number of bits of host bits (0's)
default mask 255.255.0.0 11111111 11111111 00000000 00000000
subnet mask 255.255.255.0 11111111 11111111 11111111 00000000
2^8 = 256
Findout out which subnet an IP address is on
Convert IP address and subnet mask to binary over one another. Match the bits and if both boths are 1's keep it and if not it's 0.Once done convert bits back to binary.
Ex IP 178.56.21.9 SN 255.255.255.0
IP - 10110010 00111000 00010101 00001001
SN - 11111111 11111111 11111111 00000000
This = 10110010 00111000 00010101 00000000 = 178.56.21.0 subnet
Calculate network address/1st host/last host/broadcast address
write IP given and subnet mask out in binary
Turn host bits to all 0 to calculate network address
network address +1 = 1st host
All host bits set to 1 = broadcast
broadcast address -1 = last host
IPv6 addresses are written by using eight blocks of four hexadecimal digits. Each block,
separated by colons, represents a 16-bit number. The following shows the full notation of
an IPv6 address:
2001:0DB8:3FA9:0000:0000:0000:00D3:9C5A
You can shorten an IPv6 address by eliminating any leading zeroes in blocks. By using this
technique, you can shorten the representation of the preceding address to the following:
2001:DB8:3FA9:0:0:0:D3:9C5A
You can then shorten the address even further by replacing all adjacent zero blocks as a
single set of double colons (“::”). You can do this only once in a single IPv6 address.
2001:DB8:3FA9::D3:9C5A
Because IPv6 addresses consist of eight blocks, you can always determine how many blocks
of zeroes are represented by the double colons. For example, in the previous IPv6 address,
you know that three zero blocks have been replaced by the double colons because five
blocks still appear.
Global Addresses
IPv6 global addresses are the equivalent of public addresses in IPv4 and are globally reachable
on the IPv6 portion of the Internet. The address prefix currently used for global addresses is
2000::/3, which translates to a first block value between 2000–3FFF in the usual hexadecimal
notation. An example of a global address is 2001:db8:21da:7:713e:a426:d167:37ab.
Link-Local Addresses
Link-local addresses are similar to APIPA addresses (169.254.0.0/16) in IPv4 in that they are
self-configured, nonroutable addresses used only for communication on the local subnet.
However, unlike an APIPA address, a link-local address remains assigned to an interface as a
secondary address even after a routable address is obtained for that interface. Link-local addresses always begin with “fe80”.
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