Posts Tagged ‘Ip Address’


In order for two sites to exchange replication data, they must be connected by a site link. A site link is a connection that enables replication traffic to travel between sites. Site links represent the physical connections available between sites.


Why to create Site Link?

When you create additional sites, you must select at least one site link for each site. Unless a site link is in place, connections cannot be made between computers at different sites, and replication between sites cannot take place. Additional site links are not created automatically; you must use Active Directory Sites and Services to create them.


Default Site Link

When you create the first domain in a forest, a default site link named DEFAULTIPSITELINK is also created. It includes the first site, and is located in the IP container in Active Directory. The site link can be renamed.


Site link attributes

When you create a site link, you must select the transport protocol it will use, give it a name, and add two or more sites to it. The sites are then connected. The characteristics of this connection are determined by the site link attributes, which can be configured. The connection characteristics are configured on the link, so all sites connected by a single site link will use the same replication path and transport. Configuring site link attributes is one part of configuring replication between sites. Site link attributes determine the characteristics of the connection in terms of the cost, frequency of replication traffic, and the protocols used.


Site link cost

Site link cost is a dimensionless number that represents the relative speed, reliability and preference of the underlying network. The lower the site link cost, the higher the priority for that link. For example, your organization has a site in Denver and a site in Paris with two connections between them: a high-speed connection and a dial-up connection in case the high-speed connection fails. You would configure two site links, one for each connection. Because the high-speed connection is preferable to a dial-up connection, you would configure the site link representing it with a lower cost than the site link for the dial-up line. Because the site link representing the high-speed connection has a lower cost, it has a higher priority, and that site link will always be used if possible. Setting site link cost enables you to determine the relative priority for each site link. The default cost value is 100, with possible values from one to 99999.


Site link replication Schedule

Replication schedule is another site link attribute that can be configured. When you configure the link’s schedule, you specify the times when the link is available for replication. Often, replication availability is configured for times when there is little other network traffic, for example from 1:00 A.M. to 4:00 A.M. The fewer hours a link is available for replication, the greater the latency between sites that are connected by that link. The need to have replication occur at off-peak hours should be balanced against the need for up-to-date information at each site connected by the link.


Site link replication frequency

When you configure the frequency of replication, you specify how many minutes Active Directory should wait before using the link to check for updates. The default value for replication frequency is 180 minutes, and the value you choose must fall between 15 minutes and one week. Replication frequency only applies to the times when the link is scheduled to be available. Longer intervals between replication cycles reduce network traffic and increase the latency between sites. Shorter intervals increase network traffic and decrease latency. The need to reduce network traffic should be balanced against the need for up-to-date information at each of the sites connected by the link.


Site link transport protocols

A transport protocol is a common language shared by computers to communicate during replication. Within a single site, there is only one protocol used for replication. When you create a site link, you must choose to use one of the following transport protocols:

1. Remote procedure call (RPC) over IP. RPC is an industry standard protocol for client/server communications, and provides reliable, high speed connectivity within sites. Between sites, RPC over IP enables replication of all Active Directory partitions. RPC over IP is the best transport protocol for replication between sites.

2. Simple mail transfer protocol (SMTP). SMTP supports intersite and interdomain replication of the schema, configuration, and global catalog. This protocol cannot be used for replication of the domain partition. This is because some domain operations, for example Group Policy, require the support of the File Replication service (FRS), which does not support an asynchronous transport for replication. If you use SMTP, you must install and configure a certificate authority to sign the SMTP messages and ensure the authenticity of directory updates. Additionally, SMTP does not provide the same level of data compression that RPC over IP enables.



Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and routing Internet Protocol packets. It is a way to allocate and specify the Internet addresses used in inter-domain routing more flexibly than with the original system of Internet Protocol (IP) address classes. As a result, the number of available Internet addresses has been greatly increased. CIDR is now the routing system used by virtually all gateway hosts on the Internet’s backbone network.

IP addresses are described as consisting of two groups of bits in the address: the more significant part is the network address, which identifies a whole network or subnet, and the less significant portion is the host identifier, which specifies a particular interface of a host on that network. This division is used as the basis of traffic routing between IP networks and for address allocation policies. Classful network design for IPv4 sized the network address as one or more 8-bit groups, resulting in the blocks of Class A, B, or C addresses. Classless Inter-Domain Routing allocates address space to Internet service providers and end users on any address bit boundary, instead of on 8-bit segments. In IPv6, however, the interface identifier has a fixed size of 64 bits by convention, and smaller subnets are never allocated to end users.

CIDR notation is a syntax of specifying IP addresses and their associated routing prefix. It appends to the address a slash character and the decimal number of leading bits of the routing prefix, e.g., for IPv4, and 2001:db8::/32 for IPv6.

The core function of DHCP is to assign addresses. DHCP functions at the Application Layer of the Open System Interconnection (OSI) reference model, as defined by the International Organization for Standardization (ISO) and the Telecommunication Standards Section of the International Telecommunications Union (ITU-T).

The OSI model is used for reference and teaching purposes; it divides computer networking functions into seven layers. From top to bottom, the seven layers are application, presentation,

session, transport, network, data-link, and physical


In brief, DHCP provides four key benefits to those managing and maintaining a TCP/IP network:


  • Centralized administration of IP configuration—DHCP IP configuration information can be stored in a single location and enables the administrator to centrally manage all IP configuration information. A DHCP server tracks all leased and reserved IP addresses and lists them in the DHCP console. You can use the DHCP console to determine the IP addresses of all DHCP-enabled devices on your network. Without DHCP, not only would you need to manually assign addresses, you would also need to devise a method of tracking and updating them.
  • Dynamic host configuration—DHCP automates the host configuration process for key configuration parameters. This eliminates the need to manually configure individual hosts when TCP/IP is first deployed or when IP infrastructure changes are required.
  • Seamless IP host configuration—the use of DHCP ensures that DHCP clients get accurate and timely IP configuration parameters, such as the IP address, subnet mask, default gateway, IP address of the DNS server, and so on, without user intervention. Because the configuration is automatic, troubleshooting of misconfigurations, such as mistyped numbers, is largely eliminated.
  • Flexibility and scalability—Using DHCP gives the administrator increased flexibility, allowing the administrator to more easily change IP configurations when the infrastructure changes. DHCP also scales from small to large networks. DHCP can service networks with ten clients as well as networks with thousands of clients. For very small, isolated networks, Automatic Private IP Addressing (APIPA) can be used.

Before delving into VoIP configurations, a brief introduction with terminology is necessary:


  • Public Switched Telephone Network (PSTN) —PSTN is the world’s collection of interconnected public voice telephone networks. It is also known as the Plain Old Telephone Service (POTS). It is set up and managed by the government and commercial organizations. It has evolved from the early days of Alexander Graham Bell to mostly digital, circuit-switched telephone network.
  • Private branch exchange (PBX) —This is a device located within an organization that routes telephone calls to internal extensions or to the PSTN. It provides additional features such as voicemail and call-forwarding. A PBX is less expensive than connecting an external line to every telephone. Numbers within the PBX (internal numbers) can be dialed using the last few numbers of the entire phone number and without going through the PSTN. A PBX usually has more than 125 ports.
  • Key telephone system —This is used like a PBX in small offices where far fewer phones are required. Each key telephone system supports up to a hundred ports.
  • Software IP phones —These consist of a headset that plugs into the USB or serial interface of a PC. The PC needs client software that supports IP telephony.
  • Hardware IP phones —These look like regular telephone sets, but they are plugged into a LAN switch. Most IP phones get power from the switch (power over Ethernet or PoE) and encapsulate voice data into IP frames for transmission over the LAN.
  • H.323—This was approved by the International Telecommunications Union (ITU) in 1996 as a standard for multimedia and audiovisual transmission across disparate networks. In 1998, it was followed by version 2. It also includes several functions such as bandwidth management, call control, multimedia management, and interoperability between different network types. H.323 has come to be the most popular protocol for VoIP.
  • Session initiation protocol (SIP)—SIP is IETF’s standard for multimedia communication over IP networks. It is an application-layer control protocol that initiates, manages, and terminates calls between two or more terminals. It is picking up as an alternative to H.323.

Subnetting is a technique of dividing a full Class A, B, or C network into smaller networks. It defines how 1 or more bits are taken from the host portion and added to the network portion. Following are the advantages of this technique:


  •  Saves IP addresses —Avoids the need to assign an entire IP range within a network to one location.
  •  Simplifies network management—Smaller, independent subnets can be created by routers. Internal networks can be restructured without impacting DMZ or external networks.
  •  Reduces network traffic —Links with high network traffic can be isolated to a subnet. Examples are NFS and backup subnets. NFS client (such as a filer) interfaces can be on a one subnet and backup server and dedicated client NICs on another.
  •  Improves security —It is easy to keep DMZ and front-facing networks separated from internal networks.


Subnetting requires taking a bit from the host portion and giving it to the network portion. The more bits we steal from host portion, the more the number of subnets. But more subnets come at the expense of IPs that would otherwise be used for hosts. Each new subnet requires two IP addresses: one for the network ID and the other for its broadcast ID.

Automatic Private IP Addressing


Automatic Private IP Addressing (APIPA) is a feature introduced with Windows 2000; it is also included in Windows XP and Windows Server 2003.


APIPA allows a computer that is configured to obtain an automatic IP address to assign itself an address from a private range should no DHCP server be available. APIPA assigns addresses in the range through—a range reserved by Microsoft for just this purpose.


APIPA is really designed for small networks that don’t use a DHCP server. APIPA allows computers running Windows 2000, Windows Server 2003, or Windows XP to plug into a network and recognize one another with little configuration necessary. If your network uses a DHCP server and you see that a client has been assigned an address in the APIPA range, it means the client could not locate a DHCP server.


Routing is the process of moving information along a path from a source to a destination.

On a TCP/IP network, the source and destination are called hosts and the information is broken apart into small packets that are transmitted between these hosts. The IP handles the routing of all these packets for the network.


Remember that a protocol such as TCP or UDP hands down a packet of data to the IP protocol for transmission to a remote host. IP must determine where the packet goes.

First, it compares the network ID of the local host with the network ID of the destination host identified in the packet. If the two network IDs match, the two hosts are on the same network segment and the packet can be sent directly to the destination host.


If IP determines that the network IDs of the local host and the remote host do not match, that means that the two hosts are on different network segments and the packet cannot be sent directly. Instead, IP must send the packet to a gateway, which is a router connecting one network segment to another. When this gateway receives the packet, its IP protocol goes through the process of comparing network IDs to determine the best place to send the packet. If the destination host is on one of the network segments to which the gateway is directly connected, the gateway can forward the packet straight to the destination host. Otherwise, the gateway forwards the packet on to another gateway, and then perhaps another, until the packet finally reaches its destination. Each time a packet crosses a gateway that is referred to as a hop. For example, if a packet must cross three routers to reach its destination that is considered three hops.


Usually, the source host is configured with the IP address of a default gateway, a router to which all packets are sent if the destination host is not found on the same network segment. Routers (and all devices with IP installed, for that matter) are able to consult routing tables that are stored in the router’s memory. A routing table holds information on preferred routes for various network IDs. This way, the router can determine the best gateway to which to send a packet based on the network ID of the packet’s destination host. There are two ways in which a router can build its routing table:


Static A static router has a routing table that is constructed and updated manually.

In other words, someone must actually access the routing table to create

routes the router can use.


Dynamic A dynamic router builds and updates its own routing table as it finds

appropriate routes. When it finds shorter routes, it favors those over longer routes.

Most important, dynamic routers can also share their information with other

routers on the network. Almost all the routers in use today are dynamic routers—

manual routers are just too much work. Dynamic routers use one of two common

routing protocols: Routing Information Protocol (RIP) and Open Shortest Path First



Ip Address is a unique address assigned to each computer on a network in order to identify and communicate with each other utilizing the Internet Protocol standard (IP)

Basic Format

A IP address consists of 4 parts (known as Octet), each having three digit ranging from 0 -255 separated by a decimal point.

Example of Valid IP:

10.31.11.* (* means all numbers ranging from 0-255 in last octet)

10.31.*.* (* means all numbers ranging from 0-255 in 3rd and 4th octet) (25-155 means all number ranging from 25 to 155).

Problem: What Is the IP Address of a Router?

A typical home network router possesses two IP addresses, one for the internal home (LAN) and one for the external Internet (WAN) connection. How can you find the router IP addresses?


The internal, LAN-IP address is normally set to a default, private number. Linksys routers, for example, use for their internal IP address. D-Link and Netgear routers typically use Some US Robotics routers use, and some SMC routers use No matter the brand of router, its default internal IP address should be provided in documentation. Administrators often have the option to change this IP address during router setup. In any case, however, the private LAN-IP address remains fixed once set. It can be viewed from the router’s administrative console.

The external, WAN-IP address of the router is set when the router connects to the Internet service provider. This address can also be viewed on the router’s administrative console. Alternatively, the WAN-IP address can be found by visiting a Web-based IP address lookup service like from any computer on the home LAN.

Another way to identify the public IP addresses of routers, involves executing a ping or “traceroute” command. From inside a home network, the (DOS) command “ping -r 1” will send a message through the home router that will cause its IP address to be displayed. For example, “ping -r 1” should result in a message like the following displayed on the command prompt:

Reply from bytes=32 times=293ms TTL=56

In this example, the IP address after “Route:” ( corresponds to the router WAN address.

On corporate networks, network discovery services based on SNMP can automatically determine the IP addresses of routers and many other network devices.

1. Click on “Start” in the bottom left hand corner of screen

2. Click on “Run”

3. Type in “command” and hit ok

You should now be at an MSDOS prompt screen.

4. Type “ipconfig /release” just like that, and hit “enter”

5. Type “exit” and leave the prompt

6. Right-click on “Network Places” or “My Network Places” on your desktop.

7. Click on “properties”

You should now be on a screen with something titled “Local Area Connection”, or something close to that, and, if you have a network hooked up, all of your other networks.

8. Right click on “Local Area Connection” and click “properties”

9. Double-click on the “Internet Protocol (TCP/IP)” from the list under the “General” tab

10. Click on “Use the following IP address” under the “General” tab

11. Create an IP address (It doesn’t matter what it is. I just type 1 and 2 until i fill the area up).

12. Press “Tab” and it should automatically fill in the “Subnet Mask” section with default numbers.

13. Hit the “Ok” button here

14. Hit the “Ok” button again

You should now be back to the “Local Area Connection” screen.

15. Right-click back on “Local Area Connection” and go to properties again.

16. Go back to the “TCP/IP” settings

17. This time, select “Obtain an IP address automatically”

18. Hit “Ok”

19. Hit “Ok” again

20. You now have a new IP address

With a little practice, you can easily get this process down to 15 seconds.


This only changes your dynamic IP address, not your ISP/IP address. If you plan on hacking a website with this trick be extremely careful, because if they try a little, they can trace it back