Inexpensive dial-up IP solutions

1. 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

2. Dial-up IP overview IP address IP address IP address your station Internet IP address IP address variable addresses (depend on location you dial to), shared by many users permanent addresses, used exclusively by you

3. 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)

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Dial-up IP overview • single station connected - implementations (cont.) • Linux - free UNIX • dialers - chat, dip, kermit, minicom, seyon ... • protocols - SLIP, PPP

11. 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.

12. 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

13. 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

14. 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)

15. 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)

16. 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

17. 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

18. 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

19. 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

20. 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

21. Linux - dial-in IP operations dial-in arrangement: Linux machine serves as terminal server modem pool Internet Linux 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

22. firewalling ip-forwarding Internet route advertising LAN via dial-up line overview • 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

23. IPRoute - LAN via dial-up line IPRoute PC-based Router V0.94 (shareware) features: • 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)

24. 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

25. 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

26. Linux - LAN via dial-up line overview • 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

27. 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

28. Internet Dial-up - e-mail delivery telnet mail client mbox • Telnet access to e-maill is very simple and easy to get but very uncomfortable (line mode) mail client POP daemon Internet mbox • 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

29. Dial-up - e-mail delivery smtp daemon mbox Internet spool • 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