diff --git a/Manuals/Tcpi-ug/Connectivity/Dialup/policy.docbook b/Manuals/Tcpi-ug/Connectivity/Dialup/policy.docbook index c194f0a..709c153 100644 --- a/Manuals/Tcpi-ug/Connectivity/Dialup/policy.docbook +++ b/Manuals/Tcpi-ug/Connectivity/Dialup/policy.docbook @@ -2,648 +2,4 @@ Usage Convenctions - - GNU/Linux Distribution - - The operating system used by both server and client computers - will be &TCD; release 5.5 - - I want to thank my friend Manual Chavez Manzano (Manny) - for finding a way to download this release of &TCD; and - bring it to me as a gift. - - (even higher releases might be used too). The - configuration described in this book doesn't use third party - software. All the software needed is available inside &TCD;. - - - - - - Authenticating PPP Users - - - The client computers will need to authenticate against the - server computer each time they intend to establish a PPP - connection. The username and password required by client - computers will be public and will be rarely changed. - - - - Credentials for PPP authentication - - Credentials for PPP authentication - - - - ISP Name: projects.centos.org -ISP Phone: +53043515094 - Username: faith - Password: mail4u.2k10 - - - - - - - - The server computer provides only one telephone line available - (e.g., +53043515094) to receive incoming calls. This affects - directly the possibilities a client computer has to establish - connection with the server computer in an environment where - several client computers are struggling among themselves to - establish a dial-up connection with the server computer. To - prevent this kind of issues from happening, it is innevitable - for the server computer to provide more telephone lines for - incoming calls (at least one for each user the server computer - expects to receive incoming calls from). - - - - - - One PPP Network Of Two Computers - - - The simpliest configuration we can achive over the telephone - network involves two computers only, where one computer would - be acting as server and another as client. In this - configuration, the client computer establishes connection to - the server to make use of internet services provided therein. - - - - When the client computer calls the server computer, the call - is attended by mgetty and then - passed to pppd for establishing a - PPP conversation between the two computers. The first thing - in a PPP conversation is the user authentication and then - (after a sucessful athentication), the IPCP conversation takes - place to set IP addresses and start data transmission over the - link recently created. In this configuration, the client - computer can set its IP address when configuring the Modem - device (see ) or - leave the server computer to assign one (assuming you are - calling a server computer). If you are configuring a server - computer, then it is necessary that you set the IP address and - netmask of the IP network you are planning to set, using the - Modem device configuration file. - - - - Configuring the IP address and netmask information inside - Modem device configuration file is very important in order to - prevent errors when transmitting data across the link. When - the the netmask information isn't set in the Modem device - configuration file, the pppd daemon on the server computer - tries to retrive such information from the client computer and - if the client computer didn't specify one either, the network - recently created would end up having a wrong information - (e.g., 255.255.255.255) which provokes - the point-to-point connection to fail when someone tries to - transfer data through it. - - -
- One PPP network of two computers - - One PPP network of two computers - - - -Provice-A PPP Server Province-A PPP Client ---------------------------\ /-------------------------- -192.168.1.1/24 | Modem ~~~ TelephoneLine ~~~ Modem | 192.168.1.2/24 ---------------------------/ \-------------------------- - - - - -
- - - The - describes the simpliest configuration we can implement for a - point-to-point connection. This configuration involves two - computers only, one acting as server (the server computer) and - other acting as client (the client computer). The client - computer calls the server computer to establish a PPP - connection in order to use whatever internet service the - server computer provides. In the figure we can see that there - are two IP addresses involved (192.168.1.1 and 192.168.1.2) inside the same - newtork (255.255.255.0). - - - - This configuration might be convenient for people in the same - location, near one another. Here, the client computer - establishes connection by mean of a local telephone call and - can use whatever internet service the server computer - provides. Since the connection lifetime is limited (see ) and only two - peers can be connected at the same time (assuming only one - Modem is attached to the server computer), the implementation - of some internet services like chat may be not a practical - offer for the server computer to provide. However, internet - services like e-mail fit perfectly on this environment where - more than one client computer would be struggling among - themselves for establishing connection with the server - computer (e.g., people connect to send/receive their e-mail - messages to/from the server computer). - - - - - - One PPP Network Of Several Computers - - - Based on , it is - possible to provide an extended version including several - server computers that may communicate between themselves to - distribute data collected from client computers they serve to. - For example, consider the telephone network of a country which - is organized in provinces and each province is divided in - several municipalities. In such organization, it would be - possible to set one or more server computers for each province - and let near people to dial-up on them to use whatever - internet service they provide. Later, it could be possible - for each server computer to establish a dial-up connections - with other near server computers in order to share information - from one province to another, as it is illustrated in . - - - - When setting the IP information, it is important that each - server computer sets both IP address and IP network mask - information in the Modem device configuration file so - different IP address can be use between different server - computers. It is also important that they all be configured to - use authentication between themselves before transmitting any - data across a PPP established connection so the information - being transmitted can be protected. - - - - When making telephone calls, if someone in Province-A needs to - send a message to someone in Province-C (which is far away - from Province-A and making a telephone call there would imply - a considerable amount of money), there is no need (even it is - possible and sometimes prefered) for that person to realize a - direct telephone call from Province-A to Province-C. Instead, - that person in Province-A can send its messages to the server - computer on its province (the nearest server on its location) - making a local telephone call and then, such server computer - would take care of delivering the information using other - server computers, following the same concept of nearest - delivery. - - -
- One PPP network of several computers - - One PPP network of several computers - - - -Provice-A PPP Server Province-A PPP Client ---------------------------\ /-------------------------- -192.168.1.1/24 | Modem ~~~ TelephoneLine ~~~ Modem | 192.168.1.2/24 ---------------------------/ | \-------------------------- - | -Provice-B PPP Server | Province-B PPP Client ---------------------------\ | /-------------------------- -192.168.1.3/24 | Modem ~~~ TelephoneLine ~~~ Modem | 192.168.1.4/24 ---------------------------/ | \-------------------------- - | -Provice-C PPP Server | Province-C PPP Client ---------------------------\ | /-------------------------- -192.168.1.5/24 | Modem ~~~ TelephoneLine ~~~ Modem | 192.168.1.6/24 ---------------------------/ \-------------------------- - - - - -
- - - The more distant a telephone call is, the more expensive it - is. This way, to move information from one province to - another, each server computers must be configured to send - information to the nearest province until reaching its - destination. For example, if you are in Province-A and want to - send an e-mail message to Province-D, the server computer - configured in Province-A must sed the e-mail message to - Province-B, then server in Province-B must be configured to - send such message to Province-C, and finally C to D. This is - required because making a direct call from Province-A to - Province-D would be otherwise too much expensive to pay. - - - - Since telephone calls are required to establish connections - between computers and each call costs money based on the - location and the destination, it is required to set a - convenction in how telephone calls are realized from one - server computer to another, specially if you plan to establish - connection between server computer placed on different - provices in order to exchange data between them. - - - - - - Do you make direct telephone calls to make direct data delivery? - — This configuration could be very expensive to maintain - (considering the telephone call distances), but data will be - delivered very fast to their destinations. - - - - - Do you call the nearest server computer and let it to deliver - your data to its destination? — This configuration could - be less expensive to maintain (considering the telephone call - distances), but data delivery will take much more time to - reach their destinations and there is no way to be sure it - will do. - - - - - - - Whatever calling schema be chosen, the server computers will - always talk through UUCP to transfer data from one place to - another. The server computers will operate with two IP - addresses each, unless you plan to connect one of the server - computers to a different network (Internet, maybe?). One IP - address would identify the server computer itself and the - other would identify the client computer establishing PPP - connection to the server computer. In this configuration it - is very importat that each server and client computer does - have one unique IP address. This way it would be possible to - move the information from one computer to another. Notice that - the number of PPP clients is directly related to the number of - telephone lines a server computer has configured to receive - incomming calls on. If there is only one telephone line - attached to the server computer then, only one client computer - will be able to establish connection to that server computer. - Other PPP clients will need to wait until the telephone line - gets free in order to establish connection with that server - computer. On the other hand, if the server computer has two - (or more) attached telephone lines, it would be possible to - attend incoming calls from two (or more) PPP client at the - same time. As resume, we can say that: the more telephone - lines the server computer has attached in, the more - simultaneous connections that computer will be able to - attend/realize from/to other computers. - - - - - - One PPP+Ethernet Network Of Several Computers - - - Assuming all server computers with a Modem device have also - one (or more) Ethernet interface attached (which is very - common nowadays), it would be possible to extend the - configuration described in - creating one Ethernet network for each server computer in the - configuration. For this configuration to be implemented it is - required one or more switch devices (based on the amount of - computers such network needs to have) for each ethernet - network interface a server computer has, as described in . - - -
- One PPP+Ethernet network of several computers - - One PPP+Ethernet network of several computers - - - -Province-A PPP/ETH Server Province-A PPP Client ---------------------------\ /-------------------------- -192.168.1.1/24 | Modem ~~~ TelephoneLine ~~~ Modem | 192.168.1.2/24 ---------------------------/ | \-------------------------- -192.168.0.1/24 | Ethernet | ----------------------|---- | - | | - +--------+ | - | Switch | | - +--------+ | - | | ----------------------|-- | -LAN1: 192.168.0.2-254/24 | ------------------------- | -Province-A ETH Clients | - | -Province-B PPP/ETH Server | Province-B PPP Client ---------------------------\ | /-------------------------- -192.168.1.3/24 | Modem ~~~ TelephoneLine ~~~ Modem | 192.168.1.4/24 ---------------------------/ | \-------------------------- -192.168.2.1/24 | Ethernet | ----------------------|---- | - | | - +--------+ | - | Switch | | - +--------+ | - | | ----------------------|-- | -LAN2: 192.168.2.2-254/24 | ------------------------- | -Province-B ETH Clients | - | -Province-C PPP/ETH Server | Province-C PPP Client ---------------------------\ | /-------------------------- -192.168.1.5/24 | Modem ~~~ TelephoneLine ~~~ Modem | 192.168.1.6/24 ---------------------------/ \-------------------------- -192.168.3.1/24 | Ethernet ----------------------|---- - | - +--------+ - | Switch | - +--------+ - | ----------------------|-- -LAN3: 192.168.3.2-254/24 ------------------------- -Province-C ETH Clients - - - - -
- - - In this configuration, computers connected to the switch will - also be considered as client computers. It is necessary that a - coordination be implemented at time of setting IP addresses to - new server computers so no IP address be duplicated on the - computer network. The illustration above describes one main - network (192.168.1/24) which connects - all the server computers using the telephone lines as medium - for data transmission. The Modem interface connects just one - computer at a time either client or server (assuming only one - Modem device is installed and configured in - the computer acting as server). The telephone line is used by - client computers to establish PPP connections with the server - computer and by server computers to exchange data with other - server computers, as well. On the other hand, the ethernet - interface attached to each server computer let the - administrator of each server computer to connect up to 252 - computers simultaneously, assuming a class C network as shown - above be used. - - There are also class A and class B network types which can be - used to connect much more computers than a class C network - allows to. - - - - - - - - Bridging Calls To Transfer Data - - - When the server computers call other server computers to - bridge data delivery, the server computer in, let's say, - Province-A (srv-1.a.domain.tld) will never know that there is - a server computer on Province-C (srv-1.c.domain.tld) or - Province-D (srv-1.d.domain.tld), but in Province-B - (srv-1.b.domain.tld) - only, its nearest location. So, when a message is sent from - srv-1.a.domain.tld to the server computer in - srv-1.d.domain.tld, the server computer in srv-1.a.domain.tld - contacts its nearest server computer (i.e., - srv-1.b.domain.tld) and delivers to it all messages sent to - srv-1.d.domain.tld. Later, since srv-1.b.domain.tld doesn't - know about srv-1.d.domain.tld server either, it delivers all - messages directed to srv-1.d.domain.tld to its nearest server - computer (i.e., srv-1.c.domain.tld). Later, the server - computer in srv-1.c.domain.tld, which knows about - srv-1.d.domain.tld, delivers to it all the messages it has for - it. Notice that, in order for this configuration to work, - system administrators attending the server computers must work - syncronized to garantee a well defined route for messages to - follow. Otherwise, if one of the server computers in the path - creates a route for a server computer that doesn't exist - (or doesn't define a route at all), the information will never - reach its destination when such computer is acting as a bridge - between other two server computers. - - - -+------------------------+ +------------------------+ +------------------------+ +---------------------+ -| To: bob@d.domain.tld | | To: bob@d.domain.tld | | To: bob@d.domain.tld | | Bob's mailbox | -| From: mat@a.domain.tld | | From: ana@b.domain.tld | | From: jef@c.domain.tld | | (Final destination) | -| Body: 500KB | | Body: 500KB | | Body: 500KB | | | -+---|--------------------+ +---|--------------------+ +---|--------------------+ +------------------^--+ - | | | | -----v--------------|<~~~~~~~~~>|---v----------------|<~~~~~~~~~>|---v----------------|<~~~~~~~~~>|------------------|--- -srv-1.a.domain.tld | 75Km Call | srv-1.b.domain.tld | 75Km Call | srv-1.c.domain.tld | 75Km Call | srv-1.d.domain.tld --------------------|<~~~~~~~~~>|--------------------|<~~~~~~~~~>|--------------------|<~~~~~~~~~>|---------------------- -relay to: | 5 min | relay to: | 10 min | relay to: | 15 min | -srv-1.b.domain.tld | 500KB | srv-1.c.domain.tld | 1.0MB | srv-1.d.domain.tld | 1.5MB | - - - - - Directing Calls To Transfer Data - - - When the server computers make direct telephone calls (no - bridge in-between is used to transfer data), the server - computer in Province-A (srv-1.a.domain.tld) contacts the - server computer in Province-D (srv-1.d.domain.tld) making a - direct telephone call up to it. In this configuration, the - telephone call might cost more than those in a bridged - configuration where several smaller telephone calls are dialed - in-between the final server computer; or less, considering - that when server computers in a bridged configuration exchange - data they may move data accumulated from other server - computers, while a direct telephone call would transmit data - from one server computer to another without any accumulated - data from other server computers. There is no need to - overload the server computers with foreign data when each - server computer could call themselves to transfer data - directly. - - - -+------------------------+ +---------------------+ -| To: bob@d.domain.tld | | Bob's mailbox | -| From: mat@a.domain.tld | | (Final destination) | -| Body: 500KB | | | -+--|---------------------+ +------------------^--+ - | | ----v---------------------|<~~~~~~~~~~>|-------------------|--- -srv-1.a.domain.tld | 225Km Call | srv-1.d.domain.tld --------------------------|<~~~~~~~~~~>|----------------------- -relay to: | 5 min | -srv-1.d.domain.tld | 500KB | - - - - The elapsed time in a server-to-server conversation is - directly related to the amount of data that need to be moved - from one server to another and the baud rate of the connection - established between the two Modem devices. In a direct - telephone call configuration, telephone calls could result to - be less expensive than those in bridged configurations where - server computers may accumulate traffic from other server - computers in the path. The accumulation of traffic between - server computers increases the amount of time the last server - computer in the path before the final destination needs, in - order to transmit everything to the final destination. In a - bridged telephone call configuration, server computers acting - as bridges do act as servers as well and produce their own - traffic which is added to that one already accumulated in - them from other server computers. This may provoke a heugh - traffic in a server-to-server conversation (remarkably on the - last destination before the final destination), that could be - potentially increased with each new server computer added to - the string of server computers acting as bridges one another. - - - - - - Restricting PPP Connection Lifetimes - - - The server computer restricts the lifetime of established - Modem connections to 15 minutes from the establishment moment - on. Once the connection has been established, if the link is - idle for 1 minute, the server computer will also close the - established connection to free the telephone line. This - control can be implemented through the - and options - inside the pppd's configuration - file as described in . - - - - The server computer restricts the incoming calls from client - computers every night from 10:00PM to 12:00AM. Outside this - range of time, the telephone could be answered by a person, - not a computer. This control can be implemented through a cron - job and the /etc/nologin.ttyxx file; - where ttyxx represents the device name of your Modem (e.g., - /etc/nologin.ttyACM0 would prevent the - Modem device installed in /dev/ttyACM0 - from answering calls). - - - -# Activate Modem to attend incoming calls. -59 21 * * * [ -f /etc/nologin.ttyACM0 ] && /bin/rm /etc/nologin.ttyACM0 -# Deactivate Modem to prevent incoming calls from being attended. -59 23 * * * [ ! -f /etc/nologin.ttyACM0 ] && /bin/touch /etc/nologin.ttyACM0 - - - - - - Providing Internet Services - - - The implementation of internet services which require - persistent connections (e.g., - chats) should not be considered as - a practical offer for PPP client computers. Instead, only - asynchronous services (e.g., - e-mail) should be supported for - them. This restriction is required to reduce the connection - times demanded such services. For example, consider an - environment where you establish connection with a server - computer to send/receive e-mails messages and then quickly - disconnect from it to free the telephone line so others be - able of using it. In this environment, there is no need for - you and others to be both connected at the same time to - send/receive e-mail messages to/from each other. The e-mails - sent from other person to you will be available in your - mailbox the next time you get connected to the server computer - and use your e-mail client to send/receive e-mail messages. - Likewise, you don't need to be connected to the server - computer in order to write your e-mail messages. You can - write down your messages off-line and then establish - connection once you've finished writing, just to send them out - and receive new messages that could have been probably sent to - you. - - - - Another issue related to e-mail exchange is the protocol used - to receive messages. Presently, there are two popular ways to - do this, one is through IMAP and another through POP3. When - you use IMAP protocol, e-mail messages are retained in the - server computer and aren't downloaded to client computer. - Otherwise, when you use POP3 protocol, e-mail messages are - downloaded to the client computer and removed from server - computer. Based on the resources we have and the kind of link - used by the client computer to connect the server computer, - using POP3 is rather prefered than IMAP. However both are made - available. - - - - Assuming you use IMAP protocol to read your mailbox, be aware - that you need to be connected to the server computer. Once - the connection is lost you won't be able to read your messages - (unless your e-mail client possesses a feature that let you - reading messages off-line). Moreover, you run the risk of - getting your mailbox out of space. If your mailbox gets out of - space, new messages sent to you will not be deliver to your - mailbox. Instead, they will be deferred for a period of time - (e.g., about 5 days when using - Postfix defaults) hoping you to - free the space in your mailbox to deliver them. If you don't - free space on your mailbox within this period of time, the - deferred e-mails will be bounced back to their senders and you - will never see them. On the other hand, assuming you are - using POP3 protocol to read your mailbox, you always keep your - mailbox free to receive new e-mails messages and keep them for - you until the next time you establish connection with the - server computer and download them to your client computer - using your e-mail client. - - - - The information generated inside the server computer is - isolated from Internet. This way, any information generated - inside the server computer will be available only to people - connected to the same network the server computer is connected - to. For example, don't ever expect to send/receive e-mails - to/from Internet e-mail accounts like Gmail or Yahoo, nor - visiting web sites like Google or Wikipedia either. For - this to happen, it is required an established connection - between the server computer you are establishing connection - through and the Internet network those services are available - in. Without that link, it is not possible to direct your - requests to those sites. - - - -