Networking Tips Tricks

What is a Digital Signature? An introduction to Digital Signatures Tom (Tom's public key) (Tom's private key) Tom has been given two keys. One of Tom's keys is called a Public Key, the other is called a Private Key. Tom's Co-workers:    Anyone can get Tom's Public Key, but Tom keeps his Private Key to himself Jerry Henry Jenny Tom's Public key is available to anyone who needs it, but he keeps his Private Key to himself. Keys are used to encrypt information. Encrypting information means "scrambling it up", so that only a person with the appropriate key can make it readable again. Either one of Tom's two keys can encrypt data, and the other key can decrypt that data. Jenny (shown below) can encrypt a message using Tom's Public Key. Tom uses his Private Key to decrypt the message. Any of Tom's coworkers might have access to the message Jenny encrypted, but without Tom's Private Ke...

split-mount installation with single-point building ground

A GPS unit is required for the synchronization of the TDD radio network. With the Time Division Duplex TDD operation each sector should transmit and receive at the same time, to avoid intra-cell and inter-cell interference. The GPS unit must be installed outdoors. The receiver’s antenna should be installed somewhere on the supporting structure without any obstructions on the way to the open sky. For details about the installation of the GPS unit, please refer to the guidelines of the GPS manufacturer as there is difference in mounting assembly of different manufacturers. Figure shows standard guidelines for GPS installation.

( note that basic antenna concepts may make reference to vehicular installation.  While this installation situation is not applicable to wireless broadband, the fundamental theory is very similar) Antenna An antenna is a device that transmits and/or receives electromagnetic waves. Electromagnetic waves are often referred to as radio waves. Most antennas are resonant devices, which operate efficiently over a relatively narrow frequency band. An antenna must be tuned to the same frequency band that the radio system to which it is connected operates in, otherwise reception and/or transmission will be impaired. Wavelength We often refer to antenna size relative to wavelength. For example: a half-wave dipole, which is approximately a half-wavelength long. Wavelength is the distance a radio wave will travel during one cycle. The formula for wavelength is: Note: The length of a half-wave dipole is slightly less than a half-wavelength due to end effect. The speed of propagati...

IP address (IPv4 / IPv6) is divided into 4 sub-blocks. Each sub-block has a different weight number each powered by 256. IP number is being used in the database because it is efficient to search between a range of number in database. Beginning IP number and Ending IP Number are calculated based on following formula: IP Number = 16777216*w + 65536*x + 256*y + z (Formula 1) where IP Address = w.x.y.z For example, if IP address is "202.186.13.4", then its IP Number "3401190660" is based on the Formula 1. IP Address = 202.186.13.4 So, w = 202, x = 186, y = 13 and z = 4 IP Number = 16777216*202 + 65536*186 + 256*13 + 4 = 3388997632 + 12189696 + 3328 + 4 = 3401190660 To reverse IP number to IP address, w = int ( IP Number / 16777216 ) % 256 x = int ( IP Number / 65536 ) % 256 y = int ( IP Number / 256 ) % 256 z = int ( IP Number ) % 256 IP Address = w.x.y.z where % is the mod operator and int is return the integer part of the division. In Microsoft Excel you can easily fi...

Presuppositions to the examples (1) Required functions No other service except for ftp runs on the server. Only specific registered users are allowed to access the server (no anonymous user accounts are allowed). Authenticating the user in not only a user ID and a password but also a source IP address The server provides ftp service for each user equally. (2) Platform Hardware with Linux operating system tolerable for 24 hour continuous operation Fundamental settings as an Internet server have already been done. (3) Network configuration (see Figure 9.1) Permanent connection to the Internet ( via ISP) is prepared. The server is placed in the DMZ (De-Militarized Zone) branch from a firewall. The firewall allows only ftp connections for the server. Data stored in the server are transferred from data source system(s) in intranet through the firewall. Figure 9-1. Presuppositions to examples 2 Proces...

There are many protocols that could transfer data between hosts over TCP/IP networks. Each protocol has its characteristics, Some examples are as follow 1 File Transfer Protocols (1 ) TFTP The Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol defined by RFC1350 . The mechanism of TFTP is completely different from the FTP. TFTP service uses single TCP port 69 instead o f 21 and 20 of the FTP. As the TFTP has no mechanism for authentication, it is inadequate to use it for Internet server because anybody could read/write data from/to the server. The TFTP is mainly used to boot disk-less equipment like X-11 terminals. (2) FTPS The FTPS is a extended version of the FTP. The extension to the standard FTP is define by the RFC2228 which introduce optional security function to the control and data connection and some new command and reply to the FTP are added. The encryption algorithms are not the part of the FTPS definition and installation dependent, and Se...

1 Built in FTP Clients Linux and Windows have their built in FTP client software. Those have traditional text-based user interface that could be controlled by some scripting software, like shell , but not suit for operational unattended purposes because their user interface is full duplex and scripting languages are not good at handling those asynchronous communications. #!/bin/sh ftp -n ftp.wmo.int << EOF >> logfile 2>&1 user username passrowd binary get remote-file1 bye EOF Example: Simple Shell Script for FTP 2 GUI Clients You can find much free FTP client software on the Internet. Most of them are Graphical User Interface (GUI) based client and easy to use, but not suit for unattended operation because they need human interaction to transfer files. Some shareware or commercial software has batch or automatic operation capability with error retry or/and error recovery. Net Vampire and Core FTP Pro are examples.

There are kinds of software products for FTP server. The server administrator should choose the appropriate one in consideration of security and reliability where the authors respond quickly to security issues or bugs, performance to handle necessary concurrent connections, easiness in management and maintenance at server side, compliance with RFC959, and convenience from the user view. The following software products are predominant examples in diffusion and useful features. Be sure to install the most recent version of the software and to apply most recent patches to it, whichever product you choose. 1 wu-ftpd ( http://www.wu-ftpd.org/ ) The "wu-ftpd" had merits of having functions for archiving and compressing entire elements under a directory and running on many supported platforms. The last version of the "wu-ftpd" is 2.6.2 released in Nov 2001. Since the "wu-ftpd" used to be most commonly used server software, information on security flaw an...

In this section, server management issues such as security, availability, and service constructions are described. Execution Environment (Run Mode on the Unix like OS) One major concern on establishing FTP service is the run mode of the server, i.e., stand alone or run by xinetd . (1) Stand Alone Mode (Run as daemon) On the stand-alone mode, server runs as a daemon that directly accepts connections from Clients by itself and serves for it. A daemon is a process that waits for some event and act for some service on the Linux. A daemon runs as a root process on the Linux. It is not recommended to run a service as daemon because daemon consumes memory resource even it only waits for some event and do nothing. Also it has security risk because daemon runs as root, the privileged process that tend to be the target of attacks, if once the process is compromised by using some technique like buffer overflow attack, the server may defect to the enemy and might be completely controlled...

In this section, FTP related things to design the service are considered . FTP Solutions On the view of risk management with in the recent Internet world, it is indispensable to adopt countermeasures against new risks continuously to keep the server secure after the operation. Fundamentals of security issues should be referred to the " WMO Guidance on Information Technology Security at WWW Centres" (being developed).  Generally , clustering and duplication of the serv ing system and multi-access circuits preparing for physical troubles are effective to improve availability, although it should be noted that their implementation range and details influence installation and recurrent costs. Considering human resource and cost for security and appropriate availability, self-management of the server is not always the sole solution. It m ight be worth to study the use of outsourcing services from ASP (Application Service Provider) / ISP (Internet Service Provider) s...

The File Transfer Protocol (FTP) is defined by the RFC959 based on the FTP Model illustrated in the Figure 2-3. The FTP uses two TCP/IP connections, i.e., control connection and data connection between the User and the Server. The control connection manages and controls the Server to transfer files between the Server and the User through the data connection. It is important for understanding the FTP that the RFC959 defines the protocol between User-FTP Process and Server-FTP Process, not between User and User-FTP Process nor User and Server-FTP Process, in the Model. You cannot see the conversation between the User-FTP Process and the Server-FTP Process, i.e., FTP protocol, directly, as you operate FTP through the User Interface. Figure 2-3. The FTP Model (Session Layer)

Basics on the File Transfer Protocol (FTP) In this section, mechanism of the File Transfer Protocol (FTP) is illustrated briefly. If you are familiar with the FTP protocol, you can skip this section. What is the FTP    The FTP is basic and common service to exchange files between computers, namely hosts, over TCP/IP networks e.g., private networks or Internet. The FTP supports file transmission and character code conversion when exchanging text or binary files. The use of FTP is effective in exchanging or distributing of large volume of data over private networks and/or the Internet. A structural outline of FTP service is illustrated in Figure 2-1. Figure 2-1. Structural outline of FTP service   Basically, FTP is defined in the RFC959 as a communication protocol between Server and User for exchanging files. The FTP Server stores files to be exchanged or exchanged. Users, who want to exchange files, will login to the server and PUT/GET files to/from t...