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Inexpensive dial-up IP solutions PowerPoint PPT Presentation

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Inexpensive dial-up IP solutions dial-up IP overview history - KA9Q NOS, Trumpet Winsock Win95 dial-up customization Linux - dial-out/in LAN over dial-up - MS DOS, Linux Dial-up IP overview IP address IP address IP address your station Internet IP address IP address

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Inexpensive dial-up IP solutions

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Inexpensive dial-up IP solutions

  • dial-up IP overview

  • history - KA9Q NOS, Trumpet Winsock

  • Win95 dial-up customization

  • Linux - dial-out/in

  • LAN over dial-up - MS DOS, Linux

Dial-up IP overview

IP address

IP address

IP address




IP address

IP address

variable addresses

(depend on location you dial to),

shared by many users

permanent addresses,

used exclusively by you

Dial-up IP overview

basic types of usage (cont.)

  • single machine connected via dial-up line

    • usually has no permanent IP address

    • has full access to interactive Internet services

      • WWW, Telnet, FTP, Gopher, Archie ...

    • e-mail cannot be delivered to it when it has no permanent IP address

      • user must have a mail-box located somewhere on the Internet and access it by using

        • Telnet

        • Post Office Protocol (POP2/POP3)

        • IMAP (Ineternet Message Access Protocol)

Dial-up IP overview

basic types of usage (cont.)

  • LAN connected via dial-up line

    • LAN has assigned permanent IP address prefix

    • border machine acts as a routerbetween Internet and LAN

    • border machine has 2 IP interfaces

      • to the LAN

      • to the dial-up line (and Internet)

    • routing information (i.e. IP prefix of the LAN) must be propagated to the Internet using routing protocol

    • e-mail may be delivered to any machine in the LAN

Dial-up IP overview

  • technology overview - required tools

    • tools to establish dial-up connection (dialers)

      • dial-out to remote side

      • may emulate terminal to the remote side in order to do an authentication and to send commands to the remote side, last of which is a command to leave terminal mode and switch to peer-to-peer network mode

    • tools to encapsulate IP packets which are to be sent over serial line

      • packet drivers running on a physical level according to serialline protocols

      • packet drivers (resident in memory) communicate with application via unified interface using software interrupt

Dial-up IP overview

  • technology overview - tools (cont.)

    • tools to setup IP interface (interface to packet driver) by appropriate information (e.g. IP addresses)

    • tools to forward IP datagrams between serial line port and LAN port

    • tools to advertise route to the LAN using routing protocols

Dial-up IP overview

  • technology

    • physical interface is UART (Universal Asynchronous Receiver Transmitter) of type 8250

    • physical layer protocols

      • SLIP

        • Serial Line Internet Protocol

        • very simple (almost no encapsulation)

      • PPP

        • hierarchical set of protocols

          • LCP (Link Control Protocol - physical layer)

          • IPCP (IP Control Protocol - network layer)

        • designed not only for IP

        • error checking with retransmition

Dial-up IP overview

  • technology (cont.)

    • IP interface setup

      • IP addresses of the line must be stated

        • statically (usually in some config file)

        • dynamically (using bootp or ipcp)

      • subnet mask

      • MTU (Maximal Transmission Unit)

    • other information needed

      • address of one or more nameservers

        • this may be any nameserver in the Internet

        • may be obtained via bootp

Dial-up IP overview

  • single station connected - implementations

    • MS DOS

      • dialers - usually provided together with modem

      • protocols: SLIP, PPP in form of packet driver

    • MS DOS with KA9Q NOS (Network Operating System)

      • provides dialer and supports both SLIP & PPP

    • MS Windows with Trumpet Winsock (shareware)

      • provides dialer and supports both SLIP & PPP

    • MS Windows 95

      • provides dialer and supports both SLIP & PPP

Dial-up IP overview

  • single station connected - implementations (cont.)

    • Linux - free UNIX

      • dialers - chat, dip, kermit, minicom, seyon ...

      • protocols - SLIP, PPP

Dial-up IP overview

  • LAN connected - implementations

    • MS DOS with PCroute or IPRoute programs

    • MS DOS with KA9Q NOS

    • Linux with ip-forwarding activated

    • all implementations provide

      • IP datagrams forwarded between serial line port and LAN port

      • advertising of LAN addresses to the Internet

    • some provide other functions like IP masquerading, firewalling, IP tunnelling etc.

Dial-up IP overview

  • MS DOS with slipper packet driver

    • sequence of operations

      • dial-out from the local machine using dialer

      • dial-in to the remote machine

        • some kind of login (username, password)

        • local machine becomes a terminal of the remote one

        • start SLIP operations on the remote side by command to the remote station

      • stop dialer and start slipper/cslipper on the local station

Dial-up IP overview

  • MS DOS with slipper packet driver

    • sequence of operations (cont.)

      • run application

        • declare IP address of serial interface

          • dynamic assignment

            (obtained using bootp protocol)

          • permanent assignment

            (declared in the configuration file)

        • declare other more or less important values such as

          • subnet mask

          • IP address of nameserver

Dial-up IP overview

  • MS DOS with KA9Q NOS (Network Operating System)

    • sequence of operations

      • dial-out - 2 basic possibilities

        (1) establish connection and run NOS

        (2) run NOS with autodialing feature

      • activate packet driver on serial port by attach command

      • configure IP interface

        • statically by ifconfig command

        • dynamically

          • by bootp (SLIP)

          • by IPCP (PPP)

Dial-up IP overview

  • MS Windows with Trumpet Winsock

    • provides both dialer and serial line packet drivers

      for Win 3.x (Windows 95 have its own winsock built in)

Dial-up IP overview

  • MS Windows with Trumpet Winsock

    • provides defined network API (Application Program Interface)

    • makes the applications independent of specific operating system environment

    • provides the applications with access to the TCP/IP networks

    • run over packet driver for LAN adapter

    • provides its own serial line packet driver

    • supports both SLIP and PPP protocols

    • provides a dialer for the dial-up lines

    • is shareware though not too expensive (see licence agreement)

    • the same APIs are provided by other operating systems too e.g. Windows 95, OS/2

Dial-up IP overview

  • Windows 95

    • W95 Plus package provides winsock application interface on the top of both

      • LAN adapter

      • dial-up serial line

    • overview of customization points

      • Internet Setup Wizard

        • Start-->Programs-->Accessories-->Internet Tools-->Internet Setup Wizard

        • decides what is your path to the Internet - LAN or dial-up

        • describes kind of your IP address assignement - dynamic or static

      • Internet Properties

        • Start-->Control Panel-->Internet

        • describes the servers which you may dial to

        • for each server you specify

          • phone number

          • COM port and modem parameters

      • Dial-up Scripting Tool

        • Start-->Programs-->Accessories-->Dial-up Scripting Tool

        • gives you opportunity to automate your authentication to the remote server

Dial-up IP overview

  • Linux

    • provides both SLIP and PPP

    • provides both dial-in and dial-out operations

    • sequence of operations on dial-out IP

      • SLIP

        • dial using some dialer (e.g... Kermit)

        • activate SLIP on the remote side

        • attach serial port to SLIP driver by slattach

        • configure and activate new IP interface by ifconfig

          • statically

          • dynamically by using bootp

        • dip command may be used to do all above operations at once

Dial-up IP overview

  • Linux

    • sequence of operations on dial-out IP (cont.)

      • PPP - all operations are done automatically by using pppd command with configuration options

      • dip command may be used to activate either SLIP or PPP on the line

Linux - dial-in IP operations

  • initially serial line is controlled by getty program

  • user dials-in in normal terminal emulation, logs on to the system and then a special shell is invoked with the serial line as its standard input/output device; authentication is thus performed using standard unix procedure

  • special shell attaches the serial line to the IP interface

  • line mode changes from terminal mode to peer-to-peer communcation between user machine and Linux machine

  • 3 special shells available

    • sliplogin, diplogin - for SLIP

    • ppplogin- for PPP

Linux - dial-in IP operations

dial-in arrangement: Linux machine serves as terminal server

modem pool



note:arrangement with getty as listener on serial port is typical

for Unix dial-in; alternately pppd itself may be used to listen on

serial port for incoming call; PAP or CHAP are used then

for authentication






LAN via dial-up line


  • 2 implementations represent inexpensive solution of LAN connection to the Internet

    • MS Dos application IPRoute

    • Linux

  • both applications may run on modest PC configuration (386, 4MB RAM), IPRoute even on diskless XT

  • packets are forwarded between LAN and serial interfaces

  • route to the LAN (via dial-up line) is advertised to the rest of the world using RIP

IPRoute - LAN via dial-up line

IPRoute PC-based Router V0.94 (shareware)


  • Multiple ethernet interfaces.

  • SLIP, CSLIP and asynchronous PPP serial links.

  • Demand-dial and answer scripting.

  • IP packet filtering.

  • Network Address Translation (NAT).

  • Packet and event logging to a syslog daemon.

  • Routing Information Protocol (RIP).

    supported interfaces:

  • ethernet via packet driver

  • PC UARTS (i.e. 8250/16450/16550)

PC Route - LAN via dial-up line

PC Route - PC-based Router (freeware)

  • some features

    • IP routing with Subnets

    • static routing with up to 250 routes

    • responds to ICMP echo (ping) , sends ICMP TTL, Redirect, Unreachable when appropriate

    • fragmentation where necessary

    • RIP dynamic routing protocol

    • up to 6 served interfaces of varying types

  • on LAN interface either standardized driver (Packet driver) or special built in drivers may be used

  • leased or dial-up line may be used

PC Route - LAN via dial-up line

  • customization is performed in several steps

    • macros in the source files are used to gather needed components

    • program is assembled

    • special configuration program is run to create parameter file containing various run time parameters like IP addresses

  • run time activity is logged using syslog protocol

Linux - LAN via dial-up line


  • ip-forwarding must be enabled in kernel (kernels are usually distributed with ip-forwarding disabled)

  • ip-forwarding means that machine acts as a router(datagrams received on one interface are forwarded to another one)

  • dynamic routing (usually by RIP, but any available)

  • firewalling is provided by the kernel - packets may be filtered according to their source or destination IP address and port

  • ip masquerading - ip address translation

  • dial-on-demand is suitable mechanism by which line is connected only when there are some packets to be forwarded

  • serial ip load balancing (2 V.34bis make DS0)

  • ip tunnelling

  • ip accounting

  • SNMP agents

  • ip multicasting

Linux - LAN via dial-up line

overview of Linux kernel IP networking options

[*] Network firewalls

[*] Network aliasing

[*] TCP/IP networking

[*] IP: forwarding/gatewaying

[*] IP: multicasting

[*] IP: firewalling

[*] IP: firewall packet logging

[*] IP: masquerading (EXPERIMENTAL)

[*] IP: transparent proxy support (EXPERIMENTAL)

[*] IP: always defragment

[*] IP: accounting

[ ] IP: optimize as router not host

<*> IP: tunneling

[*] IP: multicast routing (EXPERIMENTAL)

<M> IP: aliasing support

[ ] IP: PC/TCP compatibility mode

<M> IP: Reverse ARP

[ ] IP: Disable Path MTU Discovery (normally enabled)

[ ] IP: Drop source routed frames

[*] IP: Allow large windows (not recommended if <16Mb of memory)

<M> The IPX protocol

[ ] Full internal IPX network

< > Appletalk DDP

[ ] Amateur Radio AX.25 Level 2

[*] Bridging (EXPERIMENTAL)

[ ] Kernel/User network link driver


Dial-up - e-mail delivery





  • Telnet access to e-maill is very simple and easy to get but very uncomfortable (line mode)







  • POP access to e-mail is user friendly mainly because mail agent is local to the user

  • 2 types of POP

    • POP2/POP3 (Post Office Protocol)

    • IMAP (Inetrnet Message Access Protocol) - more powerful

Dial-up - e-mail delivery






  • at the time the dial-up link is not activemail must be either stored on sender’s site or spooled somewhere in the Internet usually at the addressee’s provider site

  • appropriate spooler is pointed to by MX record associated with the destination in DNS

  • after link becomes active mail must be tranfered from spooler to destination

  • how to recognize that particular link is active at the moment

    • by monitoring routing tables of appropriate routers on spooler side of link

      • may be done by using SNMP protocol

      • security exposure

    • by command sent from destination side of link after establishing the link

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