My Netwok Dictionary

A broadcast storm occurs when you receive a large amount of broadcast packets on a port. The sending of these packets can cause the network is slow or that the time limit expires. Storm control is configured for the switch as a whole but operates port. Storm control is disabled by default.

Preventing broadcast storms by setting too high or low values of threshold discards excessive broadcast MAC traffic, multicast or unicast. In addition, the configuration of securities to raise thresholds in a switch can disable the port.

STP problems include broadcast storms, loops, BPDU and dropped packets. The function of STP is to ensure that there are no logical loops in a network by designating a root bridge. The root bridge is the focal point of a spanning-tree configuration that controls the way the protocol operates. 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 »

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 »

Although the original objective of the ICMP protocol is the notify errors and unusual conditions (which require special attention with regard to the IP protocol), it is possible to make an improper use of this protocol for identifying traces of a remote system.

Here are some examples of how to obtain these tracks from the various answers given by the ICMP traffic:

ICMP echo:

The use of ICMP echo traffic allows the exploration of active systems. Thus, this exploration is to identify existing equipment within the network you want to explore, normally accessible from the Internet. Read the rest of this entry »

CHAP is used to initiate a link and check, periodically, the identity of the remote node through an exchange of signals three routes on a regular basis. CHAP is carried out upon establishing the initial link and is repeated during the time that the last link.

After completing the establishment phase of the PPP link, the host sends a test message to the remote node. The remote node responds with a value calculated by one-way hash function that, in general, Message Digest 5 (MD5). This response is based on the password and check messages. Read the rest of this entry »

The ICMP protocol does not use service port number and is therefore a little more difficult to collect details. ICMP uses a number of different types of datagrams. Many of these are harmless and normal, while others will only be observed under special circumstances. Sometimes people with too much time on their hands try to maliciously damage a user’s access to the network, generating large amounts of ICMP messages.

This is commonly called saturated ping2. While the IP accounting can not do anything to prevent this problem (although the IP firewall can help!), we can at least put accounting rules in a place that will show whether someone has been trying. ICMP does not use the ports as these do it TCP and UDP. Read the rest of this entry »

To enable the delivery of broadcast routing updates a Frame Relay in star topology, configure the central router logically assigned interfaces. These interfaces are called subinterfaces. Subinterfaces are logical subdivisions of a physical interface. In split-horizon environments, it is possible to forward routing updates received on one subinterface through another subinterface.

In a configuration of subinterfaces, each virtual circuit can be configured as a connection point to point. This allows each subinterface acts similarly to a leased line. By using a Frame Relay interface point to point, each pair of routers is point to point on its own subnet. Read the rest of this entry »

Often invites designers and network administrators to make decisions with respect to bandwidth. A decision could be on the need to increase the size of the WAN connection to add a new database. Another decision could be if the current LAN backbone bandwidth reaches for a fluid video training program.

The answers to such problems are not always easy to find, but you can start with a simple calculation of data transfer. Using the formula transfer time = size of file / bandwidth (T = S/BW), a network administrator can estimate several of the important components of network performance. If you know the typical size of a file for a given application, the file size divided by the bandwidth of the network, we obtain an estimate of the fastest time in which you can transfer the file.

There are two important points to consider when making this calculation:

• The result is only an estimate, because the size of the file does not include the added expense for the encapsulation.
• It is likely that the result is the transfer time in the best case, since the available bandwidth is rarely the theoretical maximum for the type of network.

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The model of client-server computing distributes processing across multiple computers. Distributed processing allows access to remote systems to share information and network resources. In a client-server, the client and the server share or distribute the processing responsibilities.

Most network operating systems use the client-server model to provide network services to users. The computers on a network can be called hosts, workstations, clients or servers. Any computer running TCP / IP, either a workstation or server, is considered a host computer.

The following are definitions of other terms commonly used:

• Local Host: The computer that you work at that time.
• Remote Host: A system that the user has access from another system.
• Server: Provides resources to one or more clients via a network.
• Client: A computer that uses the services of one or more servers on a network.

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