My Netwok Dictionary

Although you can use a router to segment the LAN, it is used primarily as a WAN device. Routers have LAN and WAN interfaces. In fact, routers communicate with each other through WAN connections. Routers are the backbone of the large internal networks and the Internet. It operates at Layer 3 of the OSI model, making decisions based on network addresses.

The two main functions of a router are the selection of the best route to and switching of frames to the corresponding interface. The router accomplishes this through the creation of routing tables and information sharing network of these tables with other routers. An administrator can maintain the routing tables by configuring static routes, but generally speaking, routing tables are maintained dynamically through the use of a routing protocol that exchanges information with other routers network topology (route). Read the rest of this entry »

You can configure a serial interface from the console or through a virtual terminal line. Follow these steps to configure a serial interface:

• 1.Enter global configuration mode.
• 2. Enter interface configuration mode.
• 3. Specify the interface address and subnet mask.
• 4. If the cable is DCE, set the sync speed. Skip this step if the cable is DTE.
• 5. Activate the interface.

Each active serial interface must be assigned an IP address and corresponding subnet mask, if required to interface to route IP packets. Set the IP address using the following commands:

Router (config) # interface serial 0 / 0
Router (config-if) # ip address

The serial interfaces require a synchronization signal that controls the communication. In most environments, a DCE device such as a CSU provides the signal. By default, Cisco routers are DTE devices but can be configured as DCE devices. Read the rest of this entry »

For a LAN is effective and meets the needs of users, it must be designed and implemented in accordance with a planned series of systematic steps. This article describes the following steps:

• Gather requirements and expectations
• Analyze requirements and data
• Design the structure or topology of Layers 1, 2 and 3 of the LAN
• Document the physical and logical implementation of the network

The information is gathering process to help clarify and identify any actual network problem. This information includes the history of the organization and its current status, projected growth, operational policies and procedures of administration, office systems and procedures and points of view of people who actually use the LAN. Read the rest of this entry »

The rapid growth of the Internet has left stunned most observers. One of the reasons why the Internet has grown so quickly is due to the flexibility of the original design. Without the development of new technologies for IP address assignment, the rapid growth of the Internet would have exhausted the current number of IP addresses. To compensate for this lack of IP addresses, we searched for different solutions. One solution widely deployed, is the Network Address Translation (NAT).

NAT is a mechanism for conserving registered IP addresses in large networks and simplifying management tasks IP address. Tools package is routed through a network device, usually a border router or firewall, the source IP address is translated from a private internal network address to a routable public IP address. Read the rest of this entry »

This article describes some problems of physical and logical connectivity that occur between different VLAN. When VLAN are connected together, there are some technical problems. Two of the most common problems that can arise in an environment of multiple VLAN are as follows:

• The need for end user devices to achieve non-local hosts.
• The need for the hosts in different VLAN can communicate with each other.

When a router needs to make a connection to a remote host, it checks its routing table to determine if any known route. If the remote host enters a subnet that knows how to reach the destination, the system checks if you can connect through this interface. If all known paths fail, the system has one last option, the default route. Read the rest of this entry »

A typical example of transformation is the end of the line: SMTP characters are represented, While in Unix are represented only. Another example: some mail on Unix, especially the older readers interpret that in a voicemail, the sequence of characters “From” at the beginning of the line indicates the beginning of a new message.

In these systems, when a message arrives that contains this sequence at the beginning of a line, it automatically adds “>” character in front of the line (the most modern mail readers use the Content-Length header to know where each message ends and where the next begins).

Therefore, when cryptographic operations must be applied to a message, you must do so on a canonical that is convertible to local format encoding in unambiguous way. Thus, if we have to send a confidential message, encrypt the message to canonical form when the receiver decrypts it can convert to your local format. Read the rest of this entry »

Despite the complexity of DUAL, configuring EIGRP can be relatively simple. The EIGRP configuration commands vary according to the protocol to be routed. Some examples of these protocols are IP, IPX and AppleTalk. This article describes how to configure EIGRP for IP protocol.

Follow these steps to configure EIGRP for IP routes:

1. Use the following to enable EIGRP and define the autonomous system:

router (config) # router eigrp autonomous-system-number

The autonomous system number is used to identify all routers belonging to the internetwork. This value must match all routers within the internetwork. Read the rest of this entry »

By default, routers learn routes to the destination in three different ways:

Static routes: The system administrators manually define static routes as the next hop to a destination. Static routes are useful for safety and traffic reduction as it does not know any other route.

Default routes: The system administrator manually defines default routes as the route to take when there is no known route to the destination default routes keeps routing tables shorter. When there is no entry for a destination network in a routing table, the packet is sent to the default network.

Dynamics routes: Dynamic routing means that the router will find out the routes to the destination by means of periodic updates sent from other routers. Read the rest of this entry »

This article explains how the switches and bridges filter frames. In the terms switch and bridge are synonymous. Most bridges can filter frames based on any field Layer 2 frame. For example, a bridge can be programmed to reject, without sending, all frames that originate from a particular network. As the data link layer often includes reference to a higher layer protocol, bridges usually can filter based on this parameter.

In addition, filters can be useful for managing unnecessary broadcast packets and multicast. Once the bridge has created a local address table is ready to operate. When receives the frame, it examines the destination address. If the address of the story is local, the bridge passes by. If the frame is the address of another LAN segment, the bridge copies the frame to the second segment.

• Skipping a frame is called filtering.
• Copy the frame is called send.

Read the rest of this entry »

Sometimes it is useful to view or alter the content of the kernel ARP tables, for example, when you suspect a duplicate IP address is the home of an intermittent problem on your network. The arp tool was made for situations like this. Your options are: arp [-v] [-t tipohw]-[machine] arp [-v] [-t tipohw]-s machine direccionhw arp [-v]-d machine [machine...]

All arguments hostname can be symbolic names or IP addresses in dotted quad notation. The first command displays the table row corresponding to the specified IP address or machine, or if none is passed, will display all records. For example, invoking arp in vlager would get: showing vlager, vstout and vale Ethernet addresses. The list can be limited to a hardware type specified using the option -t. The possible values are ether, ax25, or ProNet, and refer to 1 0Mbps Ethernet, AMPR AX.25, and IEEE 802.5 token ring equipment, respectively.

The option-s is used to permanently add the Ethernet address of the machine specified the ARP tables. The argument specifies hardware address, which by default is supposed to be an Ethernet address specified as six hexadecimal bytes separated by colons. You can even define the hardware addresses for other types of hardware, using the option -t. Read the rest of this entry »