BUILDING REMOTE ACCESS NETWORKS phần 2 pot

Configuring Asynchronous Remote Access Connections • Chapter 2 37 MNP 4 This class of MNP works with either synchronous or asynchronous communications with data placed into packets to reduce errors. The pack- etization also increases transmission speeds. The packet size is variable as the modem monitors the line conditions. A smaller packet is used on noisy lines and a larger packet can be used on a clean line. MNP 4 also stream- lines some information in packet headers and increases data transmission overall by approximately 22 percent. MNP 4 also provides automatic error correction. MNP 5 MNP 5 uses the same type of error correction and packetizing as MNP 4, but with a different twist. MNP 5 can alter data to reduce its size. This compression encodes data so that repeating or redundant data is eliminated and therefore is represented by fewer bits. The receiving modem decodes the data before transmitting it to the host’s serial port. The effec- tive throughput can be almost twice as much as a modem that’s not using MNP 5. Keep in mind that if the data is already compressed, such as into a ZIP or TAR file, it might actually take longer for the data to be transmitted with MNP 5. This increase in time is caused by the modem examining the data for compressibility. MNP 6, 7, 9, and 10 MNP levels 6, 7, and 9 feature enhancements in data compression and error correction. MNP Level 10 is used by a cellular modem developed by Microcom. No MNP level 8 exists. Link Access Procedure for Modems (LAPM) Link Access Procedure for Modems (LAPM) is a protocol that provides error control. LAPM is part of the V.42 specification. When a V.42 modem estab- lishes a connection with another V.42 modem, it tries to establish LAPM as the error-correction protocol. If LAPM is not negotiated, MNP is tried. In the event that MNP is not available or not negotiated, a “normal” connec- tion with no error correction or control is established. In a “normal” con- nection, error correction is typically implemented in software or the computer’s serial ports, in the program making the connection. Data Compression Protocols Data compression makes it possible to transfer more data quickly over a low bandwidth connection, such as a modem line. The suffix bis appended to a modem standard indicates data-compression capability. The ITU-T V.42bis standard, for example, specifies V.42bis as the data-compression scheme. A modem uses V.42bis only when LAPM is the error-correction protocol in use. MNP5 is the backup for the V.42bis with some V.42bis modems. A modem uses MNP 5 only when MNP is the hardware error- correction protocol in use. These data-compression and error-correction www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 37 38 Chapter 2 • Configuring Asynchronous Remote Access Connections techniques can increase data throughput dramatically. Let’s examine the difference between speed and throughput. Modem speed is a measure of the actual number of bits transmitted each second (bps). The number of bits transmitted by each baud, or change in signal state, is multiplied by the number of bauds per second. Throughput is a measure of the amount of useful data bytes transmitted. This measure is not always the same as the number bits transmitted per second. With the use of data compression, redundant or repeated bytes are stripped. Start and stop bits may also be removed, depending on the error- checking technology in use—in MNP 3, for example. As data is organized into packets to be transmitted by the modem, some data is tokenized, which means that characters are removed and replaced by fewer charac- ters to represent the removed characters during transmission. The receiving modem must reconstruct the original characters before sending it to the PC, and can do this because it is using the same data compression technology. For example, if a 9600 bps modem uses a data-compression technique that transmits only 2048 bytes for a 4096 byte file, the effective useful data transfer rate—or throughput—is twice what would be achieved using a normal 9600 bps connection. In essence, a 19,200 bps throughput rate is achieved. The modems do not actually transmit data any faster than 9600 bps, but the file is transmitted faster because the modems use fewer characters to represent the data in the file. Configuring an Asynchronous Connection There are two main types of asynchronous connections: inbound and out- bound. Inbound, as the name implies, is a connection into the modem. For example, dialing into the office is an inbound connection to the receiving modem. Outbound, on the other hand, is a connection out of the modem. For example, when you dial into the office, the modem at the calling end is making an outbound connection. Sounds pretty easy, right? Well, if you add reverse Telnet to the mix, you can be making an inbound connection to the modem from a router and then establishing an outbound connection from your previously inbound connection. Reverse Telnet will be described in more detail in the Manual Configuration section of this chapter. When connecting a modem to a router, it’s important to know how you access the modem. Asynchronous connections on a router are also called TTY lines. TTY lines are similar to the virtual type terminal (VTY) ports on a router that allow Telnet access to the unit. Lines are addressed differ- www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 38 Configuring Asynchronous Remote Access Connections • Chapter 2 39 ently on each model of router based on the following information: The AUX port is line 1 on a standard router; the last TTY line +1 on access servers such as the 2509, 2510, 2511, AS5200, and AS5300; line 65 on the 2600s and 3620s; and line 129 on the 3640. So the line number for the AUX port on a 2501 is l, while the AUX port on a 2620 is 65. Router Configuration So now that you have your modem cabled into the AUX port of your router, you are ready to start using it, right? Not quite. You still must configure the router with the appropriate parameters to communicate with the modem. You need to tell the router what line you are using, the speed, flow control, and direction in which you will be using the modem, and the application in use. Let’s start first with configuring the line, because you need to tell the router where the modem is located. This is done by going into configura- tion mode on the router and issuing the following command: Central(config)#line 129 Central(config-line)# As you can see from the information displayed on the screen, you are now in line configuration mode. By using the context-sensitive help you can see all of the commands that apply to line configuration: Line configuration commands: absolute-timeout Set absolute timeout for line discon- nection access-class Filter connections based on an IP access list activation-character Define the activation character arap Appletalk Remote Access Protocol autobaud Set line to autobaud autocommand Automatically execute an EXEC command autocommand-options Autocommand options autohangup Automatically hangup when last connection closes autoselect Set line to autoselect callback Callback settings data-character-bits Size of characters being handled www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 39 40 Chapter 2 • Configuring Asynchronous Remote Access Connections databits Set number of data bits per character default Set a command to its defaults disconnect-character Define the disconnect character dispatch-character Define the dispatch character dispatch-machine Reference a TCP dispatch state machine dispatch-timeout Set the dispatch timer domain-lookup Enable domain lookups in show commands editing Enable command line editing escape-character Change the current line’s escape character exec Start an EXEC process exec-banner Enable the display of the EXEC banner exec-character-bits Size of characters to the command exec exec-timeout Set the EXEC timeout exit Exit from line configuration mode flowcontrol Set the flow control flush-at-activation Clear input stream at activation full-help Provide help to unprivileged user help Description of the interactive help system history Enable and control the command history function hold-character Define the hold character insecure Mark line as 'insecure' for LAT international Enable international 8-bit character support ip IP options keymap-type Specify a keymap entry to use lat DEC Local Area Transport (LAT) protocol- specific configuration length Set number of lines on a screen location Enter terminal location description lockable Allow users to lock a line www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 40 Configuring Asynchronous Remote Access Connections • Chapter 2 41 logging Modify message logging facilities login Enable password checking logout-warning Set Warning countdown for absolute timeout of line modem Configure the Modem Control Lines monitor Copy debug output to the current terminal line motd-banner Enable the display of the MOTD banner no Negate a command or set its defaults notify Inform users of output from concurrent sessions ntp Configure NTP padding Set padding for a specified output character parity Set terminal parity password Set a password private Configuration options that user can set will remain in effect between terminal sessions privilege Change privilege level for line refuse-message Define a refuse banner rotary Add line to a rotary group rxspeed Set the receive speed script specify event related chat scripts to run on the line session-disconnect- Set warning countdown for session-timeout warning session-limit Set maximum number of sessions session-timeout Set interval for closing connection when there is no input traffic special-character- Size of the escape (and other special) bits characters speed Set the transmit and receive speeds start-character Define the start character stop-character Define the stop character www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 41 42 Chapter 2 • Configuring Asynchronous Remote Access Connections stopbits Set async line stop bits telnet Telnet protocol-specific configuration terminal-type Set the terminal type timeout Timeouts for the line transport Define transport protocols for line txspeed Set the transmit speeds vacant-message Define a vacant banner width Set width of the display terminal x25 X25 protocol-specific configuration Next you’ll set the speed, as it will dictate to the modem the bit rate of the data flowing between the modem and the router. First, let’s look at the line before we make any changes: Central#show line 129 Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int 129 AUX 9600/9600 - - - - - 0 1 0/0 - Line 129, Location: "", Type: "" Length: 24 lines, Width: 80 columns Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits Status: Ready Capabilities: none Modem state: Ready Group codes: 0 Modem hardware state: CTS* noDSR DTR RTS TTY NUMBER 129 Parity Error = 0 Framing Error = 0 Receive Error = 0 Overrun = 0 Outcount = 0 totalout = 39 incount = 0 totalin = 39 Special Chars: Escape Hold Stop Start Disconnect Activation ^^x none - - none Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch 00:10:00 never none not set www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 42 Configuring Asynchronous Remote Access Connections • Chapter 2 43 Idle Session Disconnect Warning never Login-sequence User Response 00:00:30 Autoselect Initial Wait not set Modem type is unknown. Session limit is not set. Time since activation: never Editing is enabled. History is enabled, history size is 10. DNS resolution in show commands is enabled Full user help is disabled Allowed transports are lat pad v120 lapb-ta mop telnet rlogin nasi. Preferred is lat. No output characters are padded No special data dispatching characters Central# Now let’s implement the speed change, then exit configuration mode to see the speed we set for the line. Let’s also change the default stop bits for the line from 2 to 1 to reduce the asynchronous framing overhead, and set the flow control to hardware (CTS/RTS): Central(config)#line 129 Central(config-line)#speed 115200 Central(config-line)#stopbits 1 Central(config-line)#flowcontrol hardware Central(config-line)#end Central#sh line 129 Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int 129 AUX 115200/115200- - - - - 0 1 0/0 - www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 43 44 Chapter 2 • Configuring Asynchronous Remote Access Connections Line 129, Location: "", Type: "" Length: 24 lines, Width: 80 columns Baud rate (TX/RX) is 115200/115200, no parity, 1 stopbits, 8 databits Status: Ready Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol Out Modem state: Ready Group codes: 0 Modem hardware state: CTS* noDSR DTR RTS TTY NUMBER 129 Parity Error = 0 Framing Error = 0 Receive Error = 0 Overrun = 0 Outcount = 0 totalout = 39 incount = 0 totalin = 39 Special Chars: Escape Hold Stop Start Disconnect Activation ^^x none - - none Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch 00:10:00 never none not set Idle Session Disconnect Warning never Login-sequence User Response 00:00:30 Autoselect Initial Wait not set Modem type is unknown. Session limit is not set. Time since activation: never Editing is enabled. History is enabled, history size is 10. DNS resolution in show commands is enabled Full user help is disabled Allowed transports are lat pad v120 lapb-ta mop telnet rlogin nasi. Preferred i s lat. www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 44 Configuring Asynchronous Remote Access Connections • Chapter 2 45 No output characters are padded No special data dispatching characters Central# You can see that the speed of the line has been set to the maximum for this platform, a Cisco 3640; you can also see the change made to the stop- bits and the flow control. The router now has the parameters it is to use when communicating with the modem. A modem on a router can be con- figured as dial-in only, dial-out only, or both. let’s look first at dial-in mode. If you go into line configuration mode on the router and look at the context-sensitive help, you’ll see that there are two commands that would configure the modem for dial-in. There are significant differences between the two commands that need to be understood before configuring your modem. Below is a list of the commands you can apply to the modem. Central(config)#line 129 Central(config-line)#modem ? CTS-Alarm Alarm device which only uses CTS for call control DTR-active Leave DTR low unless line has an active incoming connection or EXEC Dialin Configure line for a modern dial-in modem Host Devices that expect an incoming modem call InOut Configure line for incoming AND outgoing use of modem Printer Devices that require DSR/CD active answer-timeout Set interval between the time the server raises DTR in response to RING and the modem responds to CTS autoconfigure Automatically configure modem on line busyout Block calls to and from the modem Let’s focus on the modem inout and modem dialin commands. The modem dialin uses the DSR signal and supports the use of hardware flow control between the router and the modem. This configures the line for dial-in access only. An older command, modem callin, is not listed in the context-sensitive help, but can be used as long as the flowcontrol hard- ware command is not used. The modem callin command is designed for use with older modems that do not support auto-answer. The modem callin command uses CTS; when a ring is detected on the line, the router raises the DTR signal, which indicates the modem should answer the call. www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 45 46 Chapter 2 • Configuring Asynchronous Remote Access Connections Below is the output of a show line after the modem dialin command has been given. You can see that the router now can use the modem for dial-in and that the modem RI is Carrier Detect using DSR: Central#show line 129 Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int 129 AUX 115200/115200- DialIn - - - 0 1 0/0 - Line 129, Location: "", Type: "" Length: 24 lines, Width: 80 columns Baud rate (TX/RX) is 115200/115200, no parity, 1 stopbits, 8 databits Status: No Exit Banner Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol Out Modem RI is CD Modem state: Idle Group codes: 0 Modem hardware state: CTS* noDSR DTR RTS TTY NUMBER 129 Parity Error = 0 Framing Error = 0 Receive Error = 0 Overrun = 0 Outcount = 0 totalout = 39 incount = 0 totalin = 39 Special Chars: Escape Hold Stop Start Disconnect Activation ^^x none - - none Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch 00:10:00 never none not set Idle Session Disconnect Warning never Login-sequence User Response 00:00:30 Autoselect Initial Wait not set Modem type is unknown. Session limit is not set. Time since activation: never www.syngress.com 93_sbcran_02 10/16/00 11:30 AM Page 46 [...]... BAUD=11 520 0 PARITY=N X1 WORDLEN=8 &A1 &B1 &G0 &H0 &I0 &K1 &L0 &M4 &N0 &P0 &R1 &S0 &T5 &X0 &Y1 %N6 #CID=0 S00=005 S08=0 02 S 02= 043 S03=013 S04=010 S05=008 S06=0 02 S07=060 S09=006 S21=010 S10=007 S11=070 S 12= 050 S13=000 S15=000 S19=000 S 22= 017 S29= 020 S23=019 S24=150 S25=005 S26=001 S27=000 S28=008 S31=000 S38=000 S 32= 009 S33=000 S34=000 S35=000 S36=000 S37=000 S39=000 S53=000 S40=000 S41=000 S 42= 126 S43 =20 0... (1.1.1.1, 21 29) Open at OK ati5 USRobotics Courier V.Everything NVRAM Settings DIAL=PULSE B0 F1 M1 BAUD=11 520 0 PARITY=N X1 WORDLEN=8 &A1 &B1 &G0 &H0 &I0 &K1 &L0 &M4 &N0 &P0 &R1 &S0 &T5 &X0 &Y1 %N6 #CID=0 S00=001 S08=0 02 S 02= 043 S03=013 S04=010 S05=008 S06=0 02 S07=060 S09=006 S21=010 S10=007 S11=070 S 12= 050 S13=000 S15=000 S19=000 S 22= 017 S29= 020 S23=019 S24=150 S25=005 S26=001 S27=000 S28=008 www.syngress.com... protocol only www.syngress.com Modem 93_sbcran_ 02 10/16/00 11:30 AM Page 65 Configuring Asynchronous Remote Access Connections • Chapter 2 s IBM 327 8 -2 terminal with an 80-by -24 display s IBM 327 8 -2 terminal with a 24 -by-80 display s IBM 327 8-3 terminal with a 32- by-80 display s IBM 327 8-4 terminal with a 48-by-80 display s IBM 327 8-5 terminal with a 27 -by-1 32 display IBM terminals use a character format... N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level -2, * candidate default U - per-user static route, o - ODR T - traffic engineered route www.syngress.com 63 93_sbcran_ 02 10/16/00 64 11:30 AM Page 64 Chapter 2 • Configuring Asynchronous Remote Access Connections Gateway of last resort is not set C 1 92. 168.1.0 /24 ... on a test AS/400 to verify connectivity Central>telnet 1.1.1 .2 25 www.syngress.com 57 93_sbcran_ 02 58 10/16/00 11:30 AM Page 58 Chapter 2 • Configuring Asynchronous Remote Access Connections Trying 1.1.1 .2, 25 Open 22 0 TEST400 running IBM AS/400 SMTP V04R03M00 on Thu, 27 Jul 20 00 07:30: 08 -0400 quit 22 1 TEST400 running IBM AS/400 SMTP V04R03M00 Connection closing Below is a list of the options available... address of 2. 2 .2. 2 This can be useful when troubleshooting path-related issues or unknown access lists on the “normal” route the packet would take Central>telnet 1.1.1.1 /route: 1.1.1.10 2. 2 .2. 2 Rlogin does not have as many available options for the command line as Telnet The following options can be used with the rlogin command Central#rlogin 1.1.1.1 ? -l Specify remote username /user Specify remote username... TN 327 0 services TN 327 0 allows any terminal to emulate an IBM 327 0 terminal IBM 327 0 terminals allow connectivity to IBM mainframes A Cisco access server can be used to provide TN 327 0 emulation services to non-TN 327 0 users The following is a listing of the IBM 327 0 terminal types supported by Cisco IOS: Figure 2. 4 LAT Terminal Services from a Cisco Router PSTN Modem Client PC Asynchronous Traffic Access. .. data: Name LATHOST, Remote Id 1, Local Id 1 Remote credits 1, Local credits 1, Advertised Credits 3 Flags: DataA, Send Credits Max Data Slot 25 5, Max Attn Slot 25 5, Stop Reason 0 Remote Node data: Node "CENTRAL", usage 1, Interface FastEthernet0/0, Address 0010.7b38.663f Timer 109, sequence 1, Facility 0, changes 159, Product code 23 4, Product version 48 Recv 128 /91 /20 4, Xmit 129 / 82/ 1684, Bad messages:... www.syngress.com 93_sbcran_ 02 10/16/00 11:30 AM Page 59 Configuring Asynchronous Remote Access Connections • Chapter 2 lpd Printer service (515) nntp Network News Transport Protocol (119) pim-auto-rp PIM Auto-RP (496) pop2 Post Office Protocol v2 (109) pop3 Post Office Protocol v3 (110) smtp Simple Mail Transport Protocol (25 ) sunrpc Sun Remote Procedure Call (111) syslog Syslog (514) tacacs TAC Access Control System... line and see that the modem type has been detected and configured by IOS Central#sh line 129 Tty Typ Tx/Rx A Modem Roty AccO AccI 129 AUX 11 520 0/11 520 0- inout - - Uses - Noise 5 Overruns 1 0/0 Int - Idle Line 129 , Location: "", Type: "" Length: 24 lines, Width: 80 columns Baud rate (TX/RX) is 11 520 0/11 520 0, no parity, 2 stopbits, 8 databits Status: No Exit Banner, Modem Detected Capabilities: Hardware Flowcontrol . #CID=0 S00=001 S 02= 043 S03=013 S04=010 S05=008 S06=0 02 S07=060 S08=0 02 S09=006 S10=007 S11=070 S 12= 050 S13=000 S15=000 S19=000 S21=010 S 22= 017 S23=019 S24=150 S25=005 S26=001 S27=000 S28=008 S29= 020 www.syngress.com 93_sbcran_ 02. S04=010 S05=008 S06=0 02 S07=060 S08=0 02 S09=006 S10=007 S11=070 S 12= 050 S13=000 S15=000 S19=000 S21=010 S 22= 017 S23=019 S24=150 S25=005 S26=001 S27=000 S28=008 S29= 020 S31=000 S 32= 009 S33=000 S34=000. TTY line +1 on access servers such as the 25 09, 25 10, 25 11, AS 520 0, and AS5300; line 65 on the 26 00s and 3 620 s; and line 129 on the 3640. So the line number for the AUX port on a 25 01 is l, while