|
|
This chapter describes the different types of calls, interfaces, software constructs, controllers, channels, and lines that are used for dial-up remote access. It includes the following main sections:
For a complete description of the commands in this chapter, see the Cisco IOS Dial Services Command Reference publication. To locate documentation of other commands that appear in this chapter, use the command reference or master index or search online.
Three basic call types are used for dial access. These call types are discussed in the following sections:
Circuit-switched digital calls are usually ISDN 56-kbps or 64-kbps data calls that use PPP. These calls are initiated by an ISDN router, access server, or terminal adapter connected to a client workstation. Individual synchronous serial digital signal level 0 (DS0) bearer (B) channels are used to transport circuit-switched digital calls across WANs. These calls do not transmit across "old world" lines.
Figure 1 shows a Cisco 1600 series remote office router dialing in to a Cisco 3640 router positioned at a headquarters gateway.
Analog modem calls travel through traditional telephone lines and ISDN lines. Regardless of the media used, theses calls are initiated by a modem and terminate on another modem at the remote end.
Figure 2 shows a remote laptop using a V.90 internal modem to dial in to a Cisco AS5300 access server, which is loaded with 96 internal V.90 MICA technologies modems.
Asynchronous character stream calls enter the router or access server through virtual terminal (vty) lines and virtual asynchronous interfaces (vty-async). These virtual lines and interfaces terminate incoming character streams that have no physical connection to the access server or router (such as a physical serial interface). For example, if you begin a PPP session over an asynchronous character stream, a vty-async interface is created to support the call. The following types of calls are terminated on a virtual asynchronous interface: Telnet, local-area transport (LAT), V.120, TN3270, and Link Access Procedure, Balanced-terminal adapter (LAPB-TA) and packet assembler/disassembler (PAD) calls.
Figure 3 shows a dumb terminal using a modem and packet assembler/disassembler (PAD) to place a call in to an X.25 switched network. The Cisco 4700-M router is configured to support vty lines and vty-async interfaces.
Different components inside the Cisco IOS software work together to enable remote clients to dial in and send packets. Figure 4 shows one Cisco AS5300 access server receiving calls from a remote office, branch office (ROBO); small office, home office (SOHO); and modem client.
Depending on your network scenario, you may encounter all of the components in Figure 4. For example, you might decide to create a virtual IP subnet by using a loopback interface. This step saves address space. Virtual subnets can exist inside devices that you advertise to your backbone. In turn, IP packets get relayed to remote PCs, which route back to the central site.
For more information about the components in Figure 4, see the following sections:
A logical construct stores core protocol characteristics to assign to physical interfaces. No data packets are forwarded to a logical construct. Cisco uses three types of logical constructs in its access servers and routers. These constructions are described in the following sections:
An asynchronous interface assigns network protocol characteristics to remote asynchronous clients that are dialing in through physical terminal (TTY) lines and modems. (Refer to Figure 5.)
Use the interface async command to create and configure an asynchronous interface.
To enable clients to dial in, you must configure two asynchronous components: async lines and async interfaces. Asynchronous interfaces correspond to physical terminal (TTY) lines. For example, asynchronous interface 1 corresponds to TTY line 1.
Commands entered in asynchronous interface mode enable you to configure protocol-specific parameters for asynchronous interfaces, whereas commands entered in line configuration mode let you configure the physical aspects for the same port.
Specifically, you configure asynchronous interfaces to support PPP connections. An asynchronous interface on an access server or router can be configured to support the following functions:
For additional information about configuring asynchronous interfaces, see the chapter "Preparing Asynchronous Interfaces."
A group asynchronous interface is a parent interface that stores and projects core protocol characteristics to a specified range of asynchronous interfaces. Asynchronous interfaces clone protocol information from group asynchronous interfaces. No data packets arrive in a group asynchronous interface.
By setting up a group asynchronous interface, you also eliminate the need to repeatedly configure identical configuration information across several asynchronous interfaces. For example, on a Cisco AS5300 one group asynchronous interface is used instead of 96 individual asynchronous interfaces. (Refer to Figure 6.)
Use the interface group-async command to create and configure a group asynchronous interface.
The following example shows a group asynchronous configuration for a Cisco AS5300 access server loaded with one 4-port ISDN PRI card and 96 MICA modems:
as5300(config)# interface group-async 1 as5300(config-if)# ip unnumbered loopback 0 as5300(config-if)# encapsulation ppp as5300(config-if)# async mode interactive as5300(config-if)# peer default ip address pool dialin_pool as5300(config-if)# no cdp enable as5300(config-if)# ppp authentication chap pap dialin as5300(config-if)# group-range 1 96 Building configuration... as5300(config-if)#
For more information, see the chapter "Configuring Modems and Chat Scripts."
A virtual template interface stores protocol configuration information for virtual access interfaces and protocol translation sessions. (Refer to Figure 7.)
Virtual templates project configuration information to temporary virtual access interfaces triggered by multilink or virtual private dialup network session events. When a virtual access interface is triggered, the configuration attributes in the virtual template are cloned and the negotiated parameters are applied to the connection.
The following example shows a virtual template interface on a Cisco 7206 router, which is used as a home gateway in a VPDN scenario:
c7206# configure terminal c7206(config)# interface virtual-template 1 c7206(config-if)# ip unnumbered ethernet 2/1 c7206(config-if)# peer default ip address pool cisco-pool c7206(config-if)# ppp authentication chap pap c7206(config-if)# exit c7206(config)# vpdn enable c7206(config)# vpdn incoming isp cisco.com virtual-template 1 c7206(config)#
For more information, see the chapter "Configuring Virtual Template Interfaces" in the Cisco IOS Dial Services Configuration Guide: Network Services publication.
Virtual templates are used to simplify the process of configuring protocol translation to tunnel PPP or Serial Line Internet Protocol (SLIP) across X.25, Transmission Control Protocol (TCP), and local-area transport (LAT) networks. You can create a virtual interface template with the interface virtual-template command and use it for one-step and two-step protocol translation. When a user dials in through a vty line and a tunnel connection is established, the router clones the attributes of the virtual interface template onto a virtual access interface. This virtual access interface is a temporary interface that supports the protocol configuration specified in the virtual interface template. This virtual access interface is created dynamically and lasts only as long as the tunnel session is active.
The virtual template in the following example explicitly specifies PPP encapsulation. The translation is from X.25 to PPP, which enables tunneling of PPP across an X.25 network.
c7206# configure terminal Enter configuration commands, one per line. End with CNTL/Z. c7206(config)# interface virtual-template 1 c7206(config-if)# ip unnumbered ethernet 0 c7206(config-if)# peer default ip address 162.18.2.131 c7206(config-if)# encapsulation ppp c7206(config-if)# exit c7206(config)# translate x25 5555678 virtual-template 1 c7206(config)#
For more information, see the chapter "Configuring Protocol Translation and Virtual Asynchronous Devices."
A logical interface receives and sends data packets and controls physical interfaces. The Cisco IOS software provides three logical interfaces used for dial access. These interfaces are described in the following sections:
A dialer interface is a parent interface that stores and projects protocol configuration information that is common to all data (D) channels that are members of a dialer rotary group. Data packets pass through dialer interfaces, which in turn initiate dialing for inbound calls. In most cases, D channels get their core protocol intelligence from dialer interfaces.
Figure 8 shows packets coming into a dialer interface, which contains the configuration parameters common to four D channels (shown as S0:0, S0:1, S0:3, and S0:4). All the D channels are members of the same rotary group. Without the dialer interface configuration, each D channel must be manually configured with identical properties. Dialer interfaces condense and streamline the configuration process.
A dialer interface is user configurable and linked to individual B channels where it delivers data packets to their physical destinations. Dialer interfaces seize physical interfaces to cause packet delivery. If a dialer interface engages in a multilink session, a dialer interface is in control of a virtual access interface, which in turn controls S0:3 or chassis 2 S0:3, for example. A dialer interface is created with the interface dialer global configuration command.
The following example shows a fully configured dialer interface:
as5300# configure terminal Enter configuration commands, one per line. End with CNTL/Z. as5300(config)# interface dialer 0 as5300(config-if)# ip unnumbered loopback 0 as5300(config-if)# no ip mroute-cache as5300(config-if)# encapsulation ppp as5300(config-if)# peer default ip address pool dialin_pool as5300(config-if)# dialer in-band as5300(config-if)# dialer-group 1 as5300(config-if)# no fair-queue as5300(config-if)# no cdp enable as5300(config-if)# ppp authentication chap pap callin as5300(config-if)# ppp multilink as5300(config-if)#
All the D channels are members of rotary group 1.
A virtual access interface is a temporary interface that is spawned to terminate incoming PPP streams that have no physical connections. PPP streams, Layer 2 Forwarding Protocol (L2F), and Layer 2 Tunnel Protocol (L2TP) frames coming in on multiple B channels are reassembled on virtual access interfaces. These access interfaces are constructs used to terminate packets.
Virtual access interfaces obtain their set of instructions from virtual interface templates. The attributes configured in virtual templates are projected or cloned to a virtual access interfaces. Virtual access interfaces are not directly user configurable. These interfaces are created dynamically and last only as long as the tunnels or multilink sessions are active. After the sessions are ended, the virtual access interfaces disappear.
Figure 9 shows how a virtual access interface functions to accommodate a multilink session event. Two physical interfaces on two different access servers are participating in one multilink call from a remote PC. However, each Cisco AS5300 access server only has one B channel available to receive a call. All other channels are busy. Therefore all four packets are equally dispersed across two separate B channels and two access servers. Each Cisco AS5300 access server receives only half the total packets. A virtual access interface is dynamically spawned upstream on a Cisco 7206 backhaul router to receive the multilink protocol, track the multilink frames, and reassemble the packets. The Cisco 7206 router is configured to be the bundle master, which performs all packet assembly and reassembly for both Cisco AS5300 access servers.
A virtual asynchronous interface is created on demand to support calls that enter the router through a nonphysical interface. For example, asynchronous character stream calls terminate or land on nonphysical interfaces. These types of calls include inbound Telnet, LAT, PPP over character-oriented protocols (such as V.120 or X.25), and LAPB-TA and PAD calls. A virtual asynchronous interface is also used to terminate L2F/L2TP tunnels, which are often traveling companions with Multilink protocol sessions. Virtual asynchronous interfaces are not user configurable; rather, they are dynamically created and torn down on demand. A virtual asynchronous line is used to access a virtual asynchronous interface.
Figure 10 shows a variety of calls terminating on a virtual asynchronous interface. After the calls end, the interface is torn down.
Cisco controllers negotiate the following parameters between an access server and a central office: line coding, framing, clocking, DS0/time slot provisioning, and signalling.
Time slots are provisioned to meet the needs of particular network scenarios. T1 controllers have
24 time slots, and E1 controllers have 30 time slots. To support traffic flow for one ISDN PRI line in a T1 configuration, use the pri-group command. To support traffic flow for analog calls over a channelized E1 line with recEive and transMit (E&M -- also ear and mouth) signalling, use the cas-group 1 timeslots 1-30 type e&m-fgb command. Most telephone companies do not support provisioning one trunk for different combinations of time slot services, though this provisioning is supported on Cisco controllers. On a T1 controller for example, time slots 1 to 10 could run PRI, time slots 11 to 20 could run channel-associated signalling (CAS), and time slots 21 to 24 could support leased-line grouping.
The following example configures one of four T1 controllers on a Cisco AS5300 access server:
as5300# configure terminal Enter configuration commands, one per line. End with CNTL/Z. as5300(config)# controller t1 ? <0-3> Controller unit number as5300(config)# controller t1 0 as5300(config-controller)# framing esf as5300(config-controller)# linecode b8zs as5300(config-controller)# clock source line primary as5300(config-controller)# pri-group timeslots 1-24 as5300(config-controller)#
This example supports modem calls and circuit-switched digital calls over ISDN PRI.
A channelized T1 or channelized E1 line is an analog line that was originally intended to support analog voice calls, but has evolved to support analog data calls. ISDN is not sent across channelized T1 or E1 lines. Channelized T1 and channelized E1 lines are often referred to as CT1 and CE1. These channelized lines are found in "old world," non-ISDN telephone networks.
The difference between traditional channelized lines (analog) and nonchannelized lines (ISDN) is that channelized lines have no built-in D channel. That is, all 24 channels on a T1 line only carry data. The signalling is in-band or associated to the data channels. Traditional channelized lines do not support digitized data calls (for example, BRI with 2B + D). Channelized lines support a variety of in-band signal types, such as ground start, loop start, wink start, immediate start, E&M, and R2.
Signalling for channelized lines is configured with the cas-group controller configuration command. The following example configures E&M group B signalling on a T1 controller:
as5300# configure terminal Enter configuration commands, one per line. End with CNTL/Z. as5300(config)# controller t1 0 as5300(config-controller)# cas-group 1 timeslots 1-24 type ? e&m-fgb E & M Type II FGB e&m-fgd E & M Type II FGD e&m-immediate-start E & M Immediate Start fxs-ground-start FXS Ground Start fxs-loop-start FXS Loop Start r1-modified R1 Modified sas-ground-start SAS Ground Start sas-loop-start SAS Loop Start as5300(config-controller)# cas-group 1 timeslots 1-24 type e&m-fgb as5300(config-controller)# framing esf as5300(config-controller)# clock source line primary as5300(config-controller)#
Cisco routing devices support ISDN BRI and ISDN PRI both media types use B channels and D channels. Figure 11 shows how many B channels and D channels are assigned to each media type.
ISDN BRI operates over most of the copper twisted-pair telephone wiring in place. ISDN BRI delivers a total bandwidth of a 144 kbps via three separate channels. Two of the B channels operate at 64 kbps and are used to carry voice, video, or data traffic. The third channel, the D channel, is a 16-kbps signalling channel used to tell the Public Switched Telephone Network (PSTN) how to handle each of the B channels. ISDN BRI is often referred to as "2 B + D."
Enter the interface bri command to bring up and configure a single BRI interface, which is the overseer of the 2 B + D channels. The D channel is not user configurable.
The following example configures an ISDN BRI interface on a Cisco 1600 series router. The isdn spid command defines the service profile identifier (SPID) number, which is assigned by the ISDN service provider, to both B channels. Not all ISDN lines have SPIDs.
1600# configure terminal Enter configuration commands, one per line. End with CNTL/Z. 1600(config)# interface bri 0 1600(config-if)# isdn spid1 55598760101 1600(config-if)# isdn spid2 55598770101 1600(config-if)# isdn switch-type basic-ni 1600(config-if)# ip unnumbered ethernet 0 1600(config-if)# dialer map ip 192.168.37.40 name hq 5552053 1600(config-if)# dialer load-threshold 70 1600(config-if)# dialer-group 1 1600(config-if)# encapsulation ppp 1600(config-if)# ppp authentication chap pap callin 1600(config-if)# ppp multilink 1600(config-if)# no shutdown
ISDN PRI is designed to carry large numbers of incoming ISDN calls at point of presences (POPs) and other large central site locations. All the reliability and performance of ISDN BRI applies to ISDN PRI, but ISDN PRI has 23 B channels running at 64 kbps each and a shared 64 kbps
D channel that carries signalling traffic. ISDN PRI is often referred to as "23 B + D" (North America and Japan) or "30 B + D" (rest of the world).
The D channel notifies the central office switch to send the incoming call to particular timeslots on the Cisco access server or router. Each one of the B channels carries data or voice. The D channel carries signalling for the B channels. The D channel identifies if the call is a circuit-switched digital call or an analog modem call. Analog modem calls are decoded and then sent to the onboard modems. Circuit-switched digital calls are directly relayed to the ISDN processor in the router. Enter the interface serial command to bring up and configure the D channel, which is user configurable.
Figure 12 shows the logical contents of an ISDN PRI interface used in a T1 network configuration. The logical contents include 23 B channels, 1 D channel, 24 time slots, and 24 virtual serial interfaces (total number of B + D channels).
The following example is for a Cisco AS5300 access server. It configures one T1 controller for ISDN PRI, then configures the neighboring D channel (interface serial 0:23). Controller T1 0 and interface serial 0:23 are both assigned to the first PRI port. The second PRI port is assigned to controller T1 1 and interface serial 1:23, and so on. The second PRI port configuration is not shown in this example. This Cisco AS5300 access server is used as part of a stack group dial-in solution for an Internet service provider.
as5300# configure terminal Enter configuration commands, one per line. End with CNTL/Z. as5300(config)# controller t1 0 as5300(config-controller)# framing esf as5300(config-controller)# linecode b8zs as5300(config-controller)# clock source line primary as5300(config-controller)# pri-group timeslots 1-24 as5300(config-controller)# exit as5300(config)# interface serial 0:23 as5300(config-if)# ip unnumbered Loopback 0 as5300(config-if)# ip accounting output-packets as5300(config-if)# no ip mroute-cache as5300(config-if)# encapsulation ppp as5300(config-if)# isdn incoming-voice modem as5300(config-if)# dialer-group 1 as5300(config-if)# no fair-queue as5300(config-if)# compress stac as5300(config-if)# no cdp enable as5300(config-if)# ppp authentication chap as5300(config-if)# ppp multilink as5300(config-if)# netbios nbf
This section describes the different line types used for dial access. It also describes the relationship between lines and interfaces.
 |
Note Cisco devices have four types of lines: console, auxiliary, asynchronous, and virtual terminal. Different routers have different numbers of these line types. Refer to the hardware and software configuration guides that shipped with your device for exact configurations. |
Table 3 shows the types of lines that can be configured.
| Line Type | Interface | Description | Numbering Rules |
|---|---|---|---|
CON or CTY | Console | Typically used to log in to the router for configuration purposes. | Line 0. |
AUX | Auxiliary | EIA/TIA-232 data terminal equipment (DTE) port used as a backup (TTY) asynchronous port. Cannot be used as a second console port. | Last TTY line number plus 1. |
Asynchronous | Same as asynchronous interface. Used typically for remote-node dial-in sessions that use such protocols as SLIP, PPP, AppleTalk Remote Access (ARA), and XRemote. | The numbering widely varies between platforms. This number is equivalent to the maximum number of modems or asynchronous interfaces supported by your access server or router.1 | |
VTY | Virtual asynchronous | Used for incoming Telnet, LAT, X.25 PAD, and protocol translation connections into synchronous ports (such as Ethernet and serial interfaces) on the router. | Last TTY line number plus 2 through the maximum number of vty lines specified.2 |
Use the show line command to see the status of each of the lines available on a router. (Refer to Figure 13.)
The following sections describe the relationship between lines and interfaces:
Asynchronous interfaces correspond to physical terminal (TTY) lines. Commands entered in asynchronous interface mode enable you to configure protocol-specific parameters for asynchronous interfaces; commands entered in line configuration mode let you configure the physical aspects of the line port.
For example, to enable IP resources to dial in to a network through a Cisco 2500 series access server, configure the lines and asynchronous interfaces as follows.
line 1 16 login local modem inout speed 115200 flowcontrol hardware ! configures the line to autosense PPP; physical line attribute autoselect ppp
interface async 1 encapsulation ppp async mode interactive async dynamic address async dynamic routing async default ip address 198.192.16.132 ppp authentication chap
The remote node services SLIP, PPP, and XRemote are configured in asynchronous interface mode. ARA is configured in line configuration mode on virtual terminal lines or TTY lines.
Virtual terminal lines provide access to the router through a synchronous interface. Virtual terminal lines do not correspond to synchronous interfaces in the same way that TTY lines correspond to asynchronous interfaces because vty lines are created dynamically on the router, whereas TTY lines are static physical ports. When a user connects to the router on a vty line, that user is connecting into a virtual port on an interface. You can have multiple virtual ports for each synchronous interface.
For example, several Telnet connections can be made to an interface (such as an Ethernet or serial interface).
The number of virtual terminal lines available on a router is defined using the line vty number-of-lines global configuration command.
Asynchronous line configuration commands configure ports for the following options:
To enter line configuration mode, first connect to the console port of the access server and enter privileged EXEC mode. Then enter global configuration mode and finally enter line configuration mode for the asynchronous lines that you want to configure. The following example shows how you enter line configuration mode for lines 1 through 16:
c2500> enable c2500# configure terminal c2500(config)# line 1 16 c2500(config-line)#
For additional information about configuring asynchronous modem lines, see the chapter "Configuring Modems and Chat Scripts."
When you enter line configuration mode, you can specify an absolute line number or a relative line number. For example, in Figure 13, absolute line number 20 is vty 2 (line 18 is vty 0). Referring to lines in a relative format is often easier than attempting to recall the absolute number of a line on a large system. Internally, the router uses absolute line numbers.
You can view all of the absolute and relative line numbers with the show users all EXEC command. In the following sample display, absolute line numbers are listed at the far left. Relative line numbers are in the third column, after the line type. In this example, the second virtual terminal line, vty 1, is absolute line number 3.
Line User Host(s) Idle Location 0 con 0 1 aux 0 2 vty 0 incoming 0 SERVER.COMPANY.COM 3 vty 1 4 vty 2 5 vty 3 6 vty 4
Compare the line numbers in this sample display to the output from the show line command, as shown in Figure 13.
Synchronous serial interfaces default to High-Level Data Link Control (HDLC) encapsulation, and asynchronous serial interfaces default to SLIP encapsulation. Cisco IOS software provides a long list of encapsulation methods that can be set on the interface to change the default encapsulation method. See the Cisco IOS Interface Configuration Command Reference publication for a complete list and description of these encapsulation methods.
The following list summarizes the encapsulation commands available for serial interfaces used in dial configurations:
To use SLIP or PPP encapsulation, the router or access server must be configured with an IP routing protocol or with the ip host-routing command.
For more information and examples about serial interface encapsulations, see the chapters "Preparing Asynchronous Interfaces" and "Preparing Synchronous Serial Ports."
Posted: Tue Jul 18 13:22:54 PDT 2000
Copyright 1989-2000©Cisco Systems Inc.