Posts Tagged ‘Networking’

There are around 5 types of routers:

– Wired Router: These are devices that connect directly to computers using cable. One of the ports on the Wired Router allows the router to connect to a modem for receiving internet, while the other set of ports transmits the data to computers using the network cable.

– Wireless Router: This is almost same as the wired router, this device connects to the Modem using wire, but while transmitting the data it can do it in two types, the Wired and Wireless. This device converts the data packets to radio signals.

– Core Routers: A core router is a wired or wireless router that distributes Internet data packets within a network, but does not distribute data packets between multiple networks.

– Edge Routers: an edge router is a wired or wireless router that distributes Internet data packets between one or more networks, but does not distribute data packets within a network.

– Virtual Router: Unlike a physical wired or wireless router, a virtual router acts as a default router for computers sharing a network. The router functions using the Virtual Router Redundancy Protocol (VRRP), which becomes active when a primary, physical router fails or otherwise becomes disabled.

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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., 192.0.2.0/24 for IPv4, and 2001:db8::/32 for IPv6.

Here is a quick reference you can use to determine which tools to use to help locate and resolve problems with your AD network.

Q: User unable to access network resources?

Is the network functioning at all? Can you view a list of networked systems or even access resources on other computers? If not, you have network connectivity problems. The troubleshooting tools you should start with include: Event Viewer, Ping, IPCONFIG, NLTEST, NetDiag and Network Monitor.

Q: User unable to locate resources by name?

Is name resolution functioning? Can you resolve NetBIOS or domain names into IP addresses using Windows Explorer or PING? If not, you have name resolution service problems. The troubleshooting tools you should start with include: Event Viewer, NSLOOKUP, NBTSTAT and DNSCMD.

Q: User unable to log in and obtain its roaming profile?

If not, your DC is having problems. The troubleshooting tools you should start with include: Event Viewer, DCDiag, DSASTAT and NTDSUTIL.

Q: User is unable to authenticate?

Can any client log on locally or remotely? If not, your DC is not authenticating properly. The troubleshooting tools you should start with include: Event Viewer and NetSetup.

Q: User unable to access resources as expected?

Can you access objects that you should be granted access to, and are you restricted from objects that you should not have access to? If not, then either the ACLs or DC is not functioning properly. The troubleshooting tools you should start with include: Event Viewer, DSACLS, NETDOM and SDCHECK.

Other Posts related to Active Directory:

https://ignitedsoul.com/2012/07/03/troubleshooting-tools-for-common-active-directory-problems/

https://ignitedsoul.com/2012/06/22/how-the-active-directory-communication-does-happens/

https://ignitedsoul.com/2012/01/23/what-is-the-sysvol-folder/

https://ignitedsoul.com/2012/01/23/replmon/

https://ignitedsoul.com/2011/10/12/how-to-restore-the-system-state-on-a-domain-controller-2/

https://ignitedsoul.com/2011/10/12/how-many-fsmo-roles/

https://ignitedsoul.com/2011/08/10/active-directory-roles/

https://ignitedsoul.com/2011/08/01/intrasite-and-intersite-replication/

https://ignitedsoul.com/2011/07/05/active-directory-intersite-replication/

https://ignitedsoul.com/2011/07/05/support-files-of-active-directory/

https://ignitedsoul.com/2011/03/04/active-directory-naming-and-ldap/

https://ignitedsoul.com/2011/01/05/review-of-active-directory-in-server-2008/

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.

 

System area networks (SANs) represent an area of computer architecture that has evolved quickly. The term SAN in this section refers to “system” (not “storage”) area networks. After various competing standardization efforts starting in the late 1990s, the state of the SAN field became temporarily unclear. However, the technology has emerged with a richer set of

features that promise to impact the server and clustering arena.

 

A SAN uses high-speed connections to attach high-performance computers in a cluster configuration. The configuration delivers very high bandwidth of 1+ GB/sec with very low latency. They are switched, with a typical hub What’s Next 579 supporting 4 to 8 nodes. Larger SANs are built with cascading hubs with cable length limitations that vary from a few meters to a few kilometers.

 

Interconnections in a SAN differ from other existing high-performance media (such as gigabit Ethernet and ATM) in several ways. SAN adapters implement reliable transport services that are similar to TCP or SPX, but directly in hardware. SANs have very low error rates. SANs are often made highly available by deploying redundant interconnect fabrics.

 

SANs provide bulk data transfer through a remote direct memory access (RDMA) mechanism. The performance within a SAN resembles more that of a memory subsystem than a traditional network (such as an Ethernet LAN). The initiator specifies a buffer on the local system and a buffer on the remote system. Data is then transferred directly between the local and remote systems by the network adapters without involving either of the host CPUs. Both read and write operations are supported in this manner.

 

 

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.

Hubs and switches are similar in many ways. Both contain connection ports into which twisted-pair RJ-45 connectors (similar to phone RJ-11 jacks) plug. They can be administered remotely. Either can be used to create a LAN, and they funnel messages to the network backbones.

 

There are salient differences between hubs and switches, however:

 

  • Shared or dedicated bandwidth —The main distinction is how they operate. Hosts in a hub-based network share the full bandwidth, but a switch is capable of creating independent full-speed connections for any two devices on the LAN that must communicate. Each connection operates at the full switch bandwidth.
  • How they handle signals —A hub acts like a repeater. It takes an incoming frame and retransmits it to all other attached hosts. Each hub port has a single host connected to it. Hubs are dumb devices and cannot learn. Switches examine incoming frames and immediately transmit them to one or more other ports. This process is very fast. Each switch port can have a single host or a LAN segment connected to it. Switches learn media access control (MAC) addresses and build a contentaddressable memory (CAM) table.
  •  Cost —Switches are more expensive than hubs for the same number of ports because they have more powerful hardware and software capabilities. Switches have more memory, a CPU, and a complete suite of software tools to manage them. Hubs have a trimmed-down version of the firmware code.

 

Like switches, bridges are also layer 2 devices. They learn MAC addresses, filter and forward frames, and can be used to segment LANs. However, they usually have 16 or fewer ports. Much of the functionality of bridges has been moved to routers.

 

Just as routers have replaced bridges at layer 3, switches (as their cost continues to fall) may eventually replace hubs at layer 2, but that has not happened yet. Hubs, it must be pointed out, have become smarter, less expensive, and easier to set up and manage. As more and more LANs are being set up, network managers continue to deploy hubs as an easy and inexpensive way to connect printers, low-traffic servers, PCs, and management consoles. The number of installed hubs is increasing mainly because of cost and simplicity.

EF stands for “Education First”. Founded in 1965 by entrepreneur Bertil Hult, EF is a privately-held company with 16 divisions that offer a range of educational programs from language training, educational travel, and academic degrees to cultural exchanges. With a mission to break down barriers in language, culture and geography, EF has helped people of all ages and nationalities become citizens of the world.

From Berlin to Beijing, Moscow to Mexico City, Dubai to Denver, EF operates 400 schools and offices in over 50 countries. EF’s global network includes 9,000 staff and 25,000 teachers and guides. To date, EF has helped over 15 million people to learn a new language, discover the world, or earn an academic degree.

“Education First” is more than our company name. It is our corporate passion.

EF’s mission is to break down the barriers of language, culture and geography that divide us.

The Official Website

 

About EF Bangalore

It all started with the idea that rather than outsourcing our systems development and maintenance, we could do it smarter and better ourselves – with our own people!

Just over a year and a half ago, a team of people therefore came to Bangalore, the Santa Barbara of India, interviewing hundreds and hundreds of people to find the most remarkable talent the market could offer. We started small, hiring only the best of the best, and began the journey from a very tiny temporary office.

 

As the number of highly skilled people grew, we also initiated the hunt for a bigger and more suitable workplace. After months of negotiations with landlords and architects, innumerous approval stamps, vanished construction workers and delayed furniture, we finally got everything in place and moved in to our new EF office on Cambridge Road on February 1st.

The office was built on the notion that you should feel at home, even when you are in the office; it should be a place where creativity and ideas spire, where you can feel the energy and power to achieve the impossible, and where your friends and colleagues inspire you to walk the extra mile.

We in Bangalore are very proud of our new office and would love for you to come and visit, maybe have a chai in our coffee lounge or enjoy the views from our roof terrace. And, we would of course take the opportunity to show you what we can and will achieve with technology!

Get IT right! Own IT!

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 169.254.0.1 through 169.254.255.255—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

(OSPF).