|
|
This chapter describes how to configure your router for dial-on-demand routing (DDR) and dial backup. For a complete description of the commands mentioned in this chapter, refer to the "DDR Commands" chapter in the Router Products Command Reference publication.
Dial backup provides protection against WAN downtime by allowing you to configure a backup serial line circuit-switched connection. Dial backup software keeps the secondary line inactive (DTR inactive) until one of the following conditions is met:
When the software detects a lost Carrier Detect signal from the primary line device or finds that the line protocol is down, it activates DTR on the secondary line. At that time, the DCE must be set to dial the remote site. When the connection is made, the routing protocol defined for the serial line will take over the task of transmitting traffic over the dialup line.
DDR provides network connections across the Public Switched Telephone Network (PSTN). Traditionally, networks have been interconnected using dedicated lines for wide-area network (WAN) connections. With DDR, you can use modems, Integrated Service Data Network (ISDN) terminal adapters (TAs), or integrated ISDN capabilities to establish low-volume, periodic network connections over public circuit-switched networks. You can also establish dial-up connections over X.25 or Frame Relay packet-switched networks by using LAPB, X.25, or Frame Relay encapsulations.
The following protocols can be routed over DDR: AppleTalk, Banyan VINES, CLNS, DECnet, IP, IPX, and XNS. For more information see the appropriate protocol configuration chapters.
Synchronous and asynchronous interfaces can be configured for DDR connections to one or more destination networks. When a packet is received for a remote network, the router uses dialing commands to send the phone number of the destination network to a modem. The modem (DCE device) then dials the destination DCE device and establishes a connection.
Figure 8-1 illustrates a typical DDR interconnection configuration.
When DDR calls using an ISDN interface are not accepted, dialer is able to place the call again or proceed to other calls almost immediately, and does not have to wait for the dialer wait-for-carrier timer to expire. The ISDN software learns within a few seconds that a call was not accepted and always informs the dialer software, thus greatly reducing delays.
This feature is automatically enabled for all ISDN interfaces when the router software begins to run.
You can still modify the dialer wait-for-carrier timer for DDR interfaces, and the show dialer command still shows the destination number, if connected.
On the router, DDR places calls using the following methods:
A chat script is a string of text that defines the login "conversation" that occurs between two systems. It consists of expect-send pairs that define the string that the local system expects to receive from the remote system and what the local system should send as a reply.
On asynchronous lines, our routers support chat scripts used to send commands for modem dialing and logging on to remote systems. To dial a call on an asynchronous line, a chat script must be defined. If multiple chat scripts are defined, regular expressions are used for powerful pattern matching to select between many scripts. See the "Regular Expressions" appendix in the Router Products Command Reference publication for information about regular expressions.
Our routers support connections from the synchronous serial interface to any DCE device that supports V.25bis. These devices include ISDN TAs for ISDN B-channel connections. V.25bis is an International Telecommunication Union Telecommunication Standardization Sector (ITU-T) recommendation for initiating calls using in-band signaling. Depending on the type of modem or CSU/DSU you are using, ITU-T V.25bis options might be supported.
Note The ITU-T carries out the functions of the former Consultative Committee for International Telegraph and Telephone (CCITT).
The V.25bis specification describes two modes of establishing or receiving calls: the direct call mode and the addressed call mode. Routers support connections using the addressed call mode and synchronous, bit-oriented operation. The addressed call mode allows control signals and commands to be sent over the DCE data interface to establish and terminate calls. These commands are packaged in High-Level Data Link Control (HDLC) synchronous data frames.
Devices used by the router for dialing out must support certain hardware signals in addition to V.25bis. When the router drops DTR, the device must disconnect any calls that are currently connected. When the device connects to the remote end, Data Carrier Detect (DCD) must be automatically asserted.
Note For many V.25bis devices, raised DCD requires a special cable to crossover DCD and Data Set Ready (DSR) signals, because the V.25bis specification requires DSR to be raised when a connection is established.
Table 8-1 lists V.25bis options. The V.25bis options are supported in the dial string (telephone number) only if you have enabled DDR using the dialer in-band command. These options are not supported in the dial string for native ISDN Basic Rate Interfaces (BRIs). The functions of these options are nation-specific, and they might have different implementations in your country. Refer to your modem or ISDN TA manual for a list of supported options.
Table 8-1 ITU-T V.25bis Options
| Option | Description |
|---|---|
Tone. (Dialing to be continued in Dual Tone |
|
Our routers also support connections from synchronous serial lines through non-V.25bis modems. Routers connected by non-V.25bis modems must use data terminal ready (DTR) EIA signaling only.
For more information about configuring the router to support DTR dialing, see the "Configure Calls to a Single Site" section later in this chapter.
DDR supports a variety of security and access control methods including the following:
Packets that are permitted entry according to the access list are identified as "interesting" or "packets of interest." Packets that are not permitted entry or are denied entry by an access list are deemed "uninteresting."
A router activates the dial-on-demand feature when it receives an interesting packet destined for a location that can be reached over a dialed connection through a PSTN. After the router dials the destination phone number and establishes a connection, packets can be transmitted. When the transmission is complete, after a configured period of line time during which there is no interesting traffic on the line, the line is automatically disconnected.
Note TCP/IP routing protocols IS-IS, BGP, and OSPF are not recommended with DDR because they require an acknowledgment for routing updates. Because DDR lines are brought up as needed, DDR will not necessarily be active and available to send responses at the times the updates are sent.
Note Access lists must be defined before you can use DDR. If there are no access lists defined, access is implicitly denied. See the "Configuring AppleTalk" chapter for information about AppleTalk static routes defined, the "Configuring IP" chapter for information about the IP access lists with the tcp keyword specified, and the "Configuring Novell IPX" chapter for information about the IPX access lists.
When you configure dial backup, you must first decide whether you want to back up when the primary line goes down, when traffic load on the primary line exceeds the defined threshold, or both. The tasks you perform depend on your decision. Perform one or more of the tasks in the following sections to configure dial backup:
To configure dial backup, set a secondary serial interface as a backup to a primary serial interface. An external data communications equipment (DCE) device, such as a modem attached to a circuit-switched service, must be connected to the secondary serial interface. The external device must be capable of responding to a DTR signal (DTR active) by auto-dialing a connection to a preconfigured remote site. To select a backup line, perform the following task in interface configuration mode:
Note When using a BRI with dial backup, neither of the B channels can be used while the interface is in a standby mode. In addition, when used as a backup interface, only one B channel is usable. Once the backup is initiated over one B channel, the second B channel is unavailable.
The interface specified in the backup interface command can only back up one interface. For examples of selecting a backup line, see the "Dial Backup Using the Auxiliary Port Example" and the "Dial Backup Using DDR and ISDN Example" sections later in this chapter.
You can configure dial backup to activate the secondary line based on the traffic load on the primary line. The software monitors the traffic load and computes a five-minute moving average. If this average exceeds the value you set for the line, the secondary line is activated and, depending upon how the line is configured, some or all of the traffic will flow onto the secondary dialup line.
To define how much traffic should be handled at one time on an interface, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
Define the traffic load threshold as a percentage of the primary line's available bandwidth. |
You can configure a value that defines how much time should elapse before a secondary line status changes after a primary line status has changed. This means that you can define two delays:
To define these delays, perform the following task in interface configuration mode:
For examples of how to define backup line delays, see the sections "Dial Backup Using the Auxiliary Port Example" and "Dial Backup Using DDR and ISDN Example" later in this chapter.
Before you configure the asynchronous interface on the auxiliary port to support DDR, configure the line as follows:
To configure your router for dial-on-demand routing, you must perform one of the tasks in the following sections:
You can also optionally customize, enhance, and monitor DDR by performing the tasks in the following sections:
See the "DDR Configuration Examples" section later in this chapter for examples of how to configure DDR on your network.
To configure a single interface, multiple interfaces, or dialer rotary groups to place calls, perform the following tasks:
Step 2 Specify a chat script for DDR (asynchronous interfaces only).
Step 3 Configure to call a single site or multiple sites.
Step 4 Configure calling from dialer rotary groups.
The following sections describe these tasks.
You must define a chat script for dialing out on asynchronous lines, specifically the asynchronous interface on the auxiliary port. Chat scripts are used to send commands for modem dialing and logging on to remote systems.
To create a chat script, perform the following task in global configuration mode:
It is recommended that you write one chat script (a "modem" chat script) for placing a call and another one (a "system" or "login" chat script) to log onto remote systems, where required.
For an example of how to use chat scripts, see "Using Chat Scripts Example" later in this chapter.
A suggested chat script naming convention is as follows:
In other words, the syntax of the chat-script command becomes the following:
For example, if you have a Telebit t3000 modem that uses V.32bis modulation, you would name your chat script as follows:
The chat-script command could become the following:
Adhering to this naming convention allows you to specify a range of chat scripts using partial chat script names with regular expressions. This is particularly useful for dialer rotary groups and is explained further in the "Configure an Interface to Receive Calls" section later in this chapter.
After a chat script has been defined as described in the "Configuring Terminal Lines and Modem Support" chapter of this publication, it must be applied to a line or an interface before it can be used. To specify a chat script for a line, perform the following task in line configuration mode:
A maximum of one script dialer command can be configured per line. The chat script naming convention described in the "Configuring Terminal Lines and Modem Support" chapter of this publication allows you to specify a chat script by the type of the modem attached to that line as follows:
It is recommended that one chat script (a "dialer" chat script) be written for placing a call and another chat script (a "system" or "login" chat script) be written to log in to remote systems, where required.
UNIX-style regular expressions are used to match patterns and select between many scripts. This will be useful if you specify modem scripts on an interface that is used to dial multiple destinations. Dialing multiple destinations is described in the "Configure Calls to Multiple Sites" section. Regular expressions are described in the "Regular Expressions" appendix of the Router Products Command Reference publication.
You can also assign chat scripts to asynchronous interfaces for purposes other than DDR. For more information, refer to the chapter "Configuring Terminal Lines and Modem Support" in this publication.
The modem chat script becomes the default chat script for an interface. This means that it becomes the default chat script for the dialer string and dialer map commands presented in this section.
To configure an interface to call a single site, perform the following steps:
Step 2 For synchronous interfaces, specify the dial string (synchronous interfaces).
For asynchronous interfaces, specify chat scripts and dial strings.
To enable DDR and specify either DTR dialing or in-band dialing, perform one of the following tasks in interface configuration mode:
| Task | Command |
|---|---|
To call a single site over serial lines connected by non-V.25bis modems using EIA signaling only (specifically, the Data Terminal Ready [DTR] signal), you enable DDR using the dialer dtr command. A serial interface configured for DTR dialing can place calls only; it cannot accept them. Dialer rotary group leaders cannot be configured for DTR dialing.
For information about configuring the router that will receive the DTR calls, see the "Configure an Interface to Receive Calls from a Single Site" section.
To call a single site over serial lines connected by asynchronous interfaces or by V.25bis modems on synchronous interfaces, you enable DDR using the dialer in-band command. If using V.25bis modems, you can optionally specify parity. The 1984 version of the V.25bis specification states that characters must have odd parity. However, the default is no parity.
For an example of configuring an interface to support DTR dialing, see the section "DTR Dialing Configuration Example" later in this chapter.
For ISDN interfaces, the dialer in-band command is not required. The software automatically configures these interfaces to be dialer type ISDN.
Note For asynchronous interfaces that do not require a system script, a modem script must be defined for the associated line by using the script dialer line configuration command.
To place a call to a single site on an asynchronous line for which a modem script has not been assigned or a system script must be specified, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
dialer map protocol next-hop-address [modem-script |
Use the dialer map command to specify a chat script if no modem script is specified for the line or an additional (system) chat script is required to log in to the remote system.
You do not need to specify a system script if one of the following is true:
If you want to call only one remote system per interface, the dialer string command is useful. You do not need to use the dialer map command for authentication. Dialers pass the string you have defined to the external DCE. ISDN devices call the number specified in the string.
To specify the string (telephone number) to be called on serial interfaces (asynchronous or synchronous), perform the following task in interface configuration mode:
You can configure your router to call multiple sites from a single line, from multiple lines, or from a dialer rotary group.
To configure your router to call multiple sites on a single line or on multiple lines, perform the following tasks:
Step 2 Define multiple dialing destinations on the interface, or specify a string of numbers to dial.
To enable DDR on an interface, perform the following task in interface configuration mode:
To define dialing destinations, perform one of the following tasks:
Note For ISDN interfaces only, you can specify an optional speed parameter for dialer map commands if you also specify a dial string. This option informs the ISDN software whether it should place a call at 56 or 64 kbps. If you omit the ISDN speed parameter, the default is 64 kbps.
If you adhered to the chat script naming convention described earlier in this chapter, use the form [modem-script *modulation-type] in the dialer map command, as in ".*-v32bis." This allows you to specify the modulation type that is best for the system you are calling, and allows the modem type for the line to be specified by the modem chat-script command.
The period (.) is a wildcard that matches any character, and the asterisk (*) indicates that the preceding character can be duplicated multiple times. For more information about regular expressions, see the "Regular Expressions" appendix in the Router Products Command Reference publication.
If there is a modem script specified in the interface configuration command (dialer map) and a modem script specified in the line configuration command (modem chat-script), the first chat script that matches both will be used. If no script matches both, an error message is logged and the connection is not established. If there is no modem chat script specified for the line, the first chat script (chat-script global configuration command) that matches the modem script regular expression will be used. If there is a system script specified in the interface configuration command, the first chat script to match the regular expression will be used.
Configure a dialer map command for each remote destination for that interface.
Perform the following steps to configure your router to place multiple calls using a dialer rotary group.
Step 2 Enable DDR on the rotary interface.
Step 3 Define multiple dialing destinations for the rotary group.
Step 4 Assign physical interfaces to the rotary group.
Dialer rotary groups allow you to apply a single interface configuration to a set of physical interfaces. Dialer rotary groups are useful in environments that have multiple callers and calling destinations. Configure a dialer interface unless you are only using a single line for dialing out or have a single line dedicated to each destination.
Note The dialer rotary groups discussed in this chapter are on the router. The telephone company also has rotary groups that allow you to dial one rotary phone number and get connected to one of several different phone numbers. If you are using telephone company rotary groups, it is a good idea to configure dialer rotary groups on the router.
A dialer rotary group is defined by specifying a "dialer interface." The dialer interface is not a physical interface; it is an entity that allows you to propagate an interface configuration to multiple interfaces. After the dialer interface is defined by a number, interface parameters are configured for the dialer interface. Finally, physical interfaces are assigned to the dialer rotary group. Physical interfaces inherit the interface dialer configuration parameters.
After an interface configuration is propagated to a set of physical interfaces, those interfaces can be used to place calls using standard DDR criteria. When many destinations are configured, any of the physical interfaces in a rotary group can be used for outgoing calls. When traffic arrives, an interface from the rotary group is dialed. When more traffic for a different host arrives, another interface is dialed. Using the dialer interface allows you to specify one set of dialer maps that can apply to multiple physical lines.
You can define up to 9 dialer interfaces. Perform the following tasks for each dialer rotary group.
To define a rotary group, perform the following task in global configuration mode:
To enable DDR for the dialer rotary group, perform the following task in interface configuration mode:
To define multiple dialing destinations for the dialer rotary group, perform one of the following tasks in interface configuration mode:
To assign a physical interface to a dialer rotary group, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
Include the specified physical interface in a dialer rotary group in interface configuration mode. |
Interfaces in a dialer rotary group do not have individual addresses; when the interface is being used for dialing, it inherits the parameters configured for the dialer interface. However, if the individual interface is configured with an address and it is subsequently used to establish a connection from the user EXEC level, the individual interface address again applies.
You cannot assign ISDN BRI interfaces to a rotary group. By default, ISDN interfaces are a rotary group of Channel B1 and Channel B2.
Note When you look at your configuration file, commands will not appear in the order in which you entered them. You will also see interface configuration commands that you did not enter, because interfaces inherit the parameters of the dialer interface in the dialer rotary group to which each interface has been assigned.
Figure 8-2 illustrates how dialer interfaces work. In this example configuration, serial interfaces 1, 2, and 3 are assigned to dialer rotary group 1. This means that these three interfaces take on the parameters configured for dialer interface 1. For example, when it is being used for dialing, the IP address of serial interface 2 is the same as the address of the dialer interface, 131.108.1.1.
You can configure an interface or dialer rotary group to receive calls from a single site or from multiple sites. To configure a single line or multiple lines to receive calls from single or multiple sites, simply enable DDR. To receive calls from multiple sites on a dialer rotary group, configure the dialer rotary group to authenticate the caller.
Perform one of the following tasks to configure an interface to receive calls:
Note CHAP or PAP is required for caller identification on dialer rotary groups receiving calls from multiple sites and is described later in this section. CHAP or PAP can also be used for authentication only, in which case, an accompanying dialer map command is not required.
To configure an interface to receive a call from a single site, enable DDR using the dialer-in-band command. Dialers specified by this command use chat scripts for asynchronous interfaces and V.25bis on synchronous interfaces. Parity is not needed to enable DDR to receive calls only.
To receive calls from an interface that is using DTR dialing, an interface can be configured for in-band dialing or not configured for anything but encapsulation, depending on the desired behavior. If the receiving interface is expected to terminate a call when no traffic is received for some time, in-band dialing must be configured (along with access lists and a dummy dialer string). If the receiving interface is purely passive, no additional configuration is necessary.
To enable DDR and thus configure an interface to receive calls from a single site, perform the following task in interface configuration mode:
You cannot set up an ISDN interface to receive calls from a single site.
You can configure your router to receive calls from multiple sites on a single line, on multiple lines, or on a dialer rotary group.
No special configuration is required to receive calls on individual lines.
To configure your router to receive calls on a dialer rotary group, follow these steps:
Step 2 Enable DDR on the rotary interface.
Step 3 Enable and configure CHAP or PAP authentication.
Step 4 Assign physical interfaces to dialer rotary groups.
Dialer rotary groups allow you to apply a single interface configuration to a set of physical interfaces. Dialer rotary groups are useful in environments that have multiple callers and calling destinations. Configure a dialer interface unless you are only using a single line for dialing out.
A dialer rotary group is defined by specifying a "dialer interface." The dialer interface is not a physical interface; it is an entity that allows you to propagate an interface configuration to multiple interfaces. After you define the dialer interface by assigning it a number, you configure interface parameters for the dialer interface. Then, you assign physical interfaces to the dialer rotary group. Physical interfaces inherit the interface dialer configuration parameters.
After an interface configuration is propagated to a set of physical interfaces, those interfaces can be used to place calls using standard DDR criteria. When many destinations are configured, any of the physical interfaces in a rotary group can be used for outgoing calls. When traffic arrives, an interface from the rotary group is dialed. When more traffic for a different host arrives, another interface is dialed. Using the dialer interface allows you to specify one set of dialer maps that can apply to multiple physical lines.
Note The dialer rotary groups discussed in this chapter are on the router. The telephone company also has rotary groups that allow you to dial one rotary phone number and get connected to one of several different phone numbers.
You can define up to nine dialer interfaces. For each dialer rotary group, perform the following task in global configuration mode:
To receive a call from multiple sites, you enable DDR using the dialer-in-band command. Dialers specified by this command use chat scripts for asynchronous interfaces and V.25bis on synchronous interfaces. Parity is not needed to enable DDR to receive calls only. To enable DDR, perform the following task in interface configuration mode:
The Point-to-Point Protocol (PPP) with Challenge Handshake Authentication Protocol (CHAP) authentication or Password Authentication Protocol (PAP) is often used to inform the central site about which remote routers are connected to it.
With this authentication information, if another packet is received for a destination to which the router is already connected, an additional call will not be placed. However, if using rotaries, the packet will be sent out the correct port.
CHAP and PAP are specified in RFC 1334. These protocols are supported on synchronous and asynchronous serial interfaces. When using CHAP or PAP authentication, each router identifies itself by a name, which informs the other router what routers are currently connected to it. This identification process prevents a router from placing a call to another router if it is already connected to that router and prevents unauthorized access. See the "Configuring Interfaces" chapter in this manual for more information about CHAP and PAP.
When CHAP is enabled, a remote device (a PC, workstation, or router) attempting to connect to the local router is requested, or challenged, to respond. The challenge consists of a random number and the host name of the local router. This challenge is transmitted to the remote device. The required response is an encrypted version of a secret password, or secret, plus a random value and the name of the remote device.
The remote device finds the secret by looking up the host name that was received in the challenge. When the local router receives the challenge response, it verifies the response by looking up the name of the remote device given in the response. The secret passwords must be identical on the remote device and the local router. These names and secret passwords are configured using the username command.
By transmitting this response, the secret is never transmitted, preventing other devices from stealing it and gaining illegal access to the system. Without the proper response, the remote device cannot connect to the local router.
CHAP transactions occur only at the time a link is established. The local router does not issue a challenge during the rest of the call. (The local router can, however, respond to such requests from other devices during a call.)
When PAP is enabled, the remote router attempting to connect to the local router is required to send an authentication request. If the username and password specified in the authentication request are accepted, the router sends an authentication acknowledgment.
To use CHAP or PAP, you must perform the following tasks:
Step 2 Enable CHAP or PAP on the interface. After you have enabled one of these protocols, the local router requires authentication from remote devices. If the remote device does not support CHAP, no traffic will be passed to that device.
Step 3 For CHAP, configure host name authentication and the secret or password for each remote system with which authentication is required.
To enable PPP encapsulation, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| 1This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication. |
To enable CHAP or PAP on an interface configured for PPP encapsulation, perform one of the following tasks in interface configuration mode:
| Task | Command |
|---|---|
After you have enabled CHAP or PAP, the local router requires authentication from remote devices that are calling in. If the remote device does not support the authentication protocol, no traffic will be passed to that device.
To specify the password to be used in CHAP caller identification, perform the following task in global configuration mode:
Add a username entry for each remote system from which the local router requires authentication.
The host name of each site calling in to the local router needs to be mapped to its address. To map a next hop address to a host name (case-sensitive), perform the following task in interface configuration mode:
| Task | Command |
|---|---|
Configure a serial interface to map host names to next hop addresses (for rotary groups only). |
To assign a physical interface to a dialer rotary group, perform the following task in interface configuration mode:
Interfaces in a dialer rotary group do not have individual addresses; when the interface is being used for dialing, it inherits the parameters configured for the dialer interface. However, if the individual interface is configured with an address and it is subsequently used to establish a connection from the user EXEC level, the individual interface address again applies.
Perform tasks in one of the following sections to configure an interface to place and receive calls:
You can configure an interface or dialer rotary group to both place and receive calls. If the interface is calling and being called by a single site, simply enable DDR and specify a dialer string. For calling and receiving calls from multiple sites, an interface or dialer rotary group must be configured to authenticate callers and to map next hop addresses to phone numbers or dial strings.
To configure your router to place calls to and receive calls from a single site, perform the following tasks in interface configuration mode:
Step 2 Specify the phone number to dial.
When a dialer string is configured on an interface and CHAP is not, any incoming call is assumed to be from the configured dialer string.
To call and receive a call from a single site, you enable DDR using the dialer-in-band command. Dialers specified by this command use chat scripts on asynchronous interfaces and V.25bis on synchronous interfaces. If using V.25bis, you can optionally specify parity. The 1984 version of the V.25bis specification states that characters must have odd parity. However, the default is no parity. To enable DDR, perform the following task in interface configuration mode:
To specify a dial-string destination for an interface, perform the following task in interface configuration mode:
To configure a single line, multiple lines, or a rotary group to place calls to and receive calls from multiple sites, perform the following tasks in interface configuration mode:
Step 2 Specify a phone number to dial.
Step 3 Map next hop to host name and phone number.
To call and receive calls from multiple sites, you enable DDR using the dialer-in-band command. Dialers specified by this command use chat scripts on asynchronous interfaces and V.25bis on synchronous interfaces. If using V.25bis, you can optionally specify parity. The 1984 version of the V.25bis specification states that characters must have odd parity. However, the default is no parity. To enable DDR, perform the following task in interface configuration mode:
To specify one destination dial string per interface, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
Specify a string of numbers to dial (to configure one phone number on multiple lines only). |
Calls from the multiple sites will need to be authenticated. Authentication can be done through CHAP. To enable CHAP on an interface and authenticate sites that are calling in, perform the following tasks in interface configuration mode:
| Task | Command |
|---|---|
dialer map protocol next-hop-address [modem-script modem-regexp] [system-script system-regexp] name hostname dial-string[:isdn-subaddress] |
| 1This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication. |
See the "Create Chat Scripts for Asynchronous Interfaces" section and the "Specify Chat Scripts for DDR" section for an explanation of assigning chat scripts to an interface or dialer rotary group.
Figure 8-3 shows a configuration in which the central site is calling and receiving calls from multiple sites. In this configuration, multiple sites are calling in to a central site, and the central site is calling out to the remote sites.
Snapshot routing, which is available on serial and ISDN lines, is a method of learning remote routes dynamically and then keeping the routes available for a period of time while regular routing updates are not being exchanged. This might be during periods when a remote site is not dialed into the local site or when a remote site has a dedicated connection to the local site but wishes to avoid the overhead of exchanging routing updates. Snapshot routing allows you to avoid configuring static routes when using dial-on-demand routing. It also eliminates the overhead required for sending periodic updates over dedicated serial lines.
When configuring snapshot routing, you choose one router on the interface to be the client router and one or more other routers to be server routers. The client router determines the frequency at which routing information is exchanged between routers.
Routing information is exchanged during an active period. During the active period a client router dials all the remote server routers for which it has a snapshot dialer map defined in order to get routes from all the remote locations. The server router provides information about routes to each client router that calls.
At the end of the active period, the router takes a snapshot of the entries in the routing table. These entries remain frozen during a quiet period. At the end of the quiet period, another active period starts during which routing information is again exchanged. See Figure 8-4.
When the router transitions from the quiet period to the active period, the line might not be available for a variety of reasons. For example, the line might be down or busy, or the PVC might be down. If this happens, the router has to wait through another entire quiet period before it can update its routing table entries. This might be a problem if the quiet period is very long, for example, around 12 hours.
Snapshot routing is useful in two command situations:
The following routing protocols support snapshot routing. Note that these are all distance-vector protocols.
To configure snapshot routing, perform the tasks described in the following sections:
To monitor and maintain snapshot routing, see the "Monitor DDR Connections and Snapshot Routing" section.
To configure snapshot routing on the client router that is connected to a dedicated serial line, perform the following steps starting in global configuration mode:
| Task | Command |
|---|---|
| Step 1. Specify a serial interface. | |
| Step 2. Configure the client router. | snapshot client active-time quiet-time [suppress-statechange-updates] [dialer] |
| 1This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication. |
To configure snapshot routing on the client router connected to an interface configured for DDR, perform the following steps starting in global configuration mode:
| 1This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication. |
Repeat Step 5 for each map you want to define. Maps must be provided for all the remote server routers this client router is to call during each active period.
ISDN BRI and PRI automatically have rotary groups, so you do not need to define a rotary group when configuring snapshot routing. To configure snapshot routing on the client router over an interface configured for BRI or PRI, perform the following steps:
| Task | Command |
|---|---|
| Step 1. Specify a BRI interface. | |
| Step 2. Configure the client router. | snapshot client active-time quiet-time [suppress-statechange-updates] [dialer] |
| Step 3. Define a dialer map. |
| 1This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication. |
Repeat step Step 3 for each map you want to define.
To configure snapshot routing on the server router that is connected to a dedicated serial line, perform the following steps starting in global configuration mode:
| Task | Command |
|---|---|
| Step 1. Specify a serial interface. | |
| Step 2. Configure the server router. |
| 1This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication. |
To configure snapshot routing on the associated server router connected to an interface configured for DDR or over a BRI or PRI interface, perform the following steps beginning in global configuration mode:
| Task | Command |
|---|---|
| Step 1. Specify a serial interface. | |
| Step 2. Specify a dialer interface. | |
| Step 3. Configure the server router. |
| 1This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication. |
The active period for the client router and its associated server routers should be the same.
Dial-on-demand routing over serial lines now supports LAPB encapsulation, in addition to the previously supported PPP, HDLC, and X.25 encapsulations.
LAPB encapsulation is supported on synchronous serial, ISDN, and dialer rotary group interfaces, but not on asynchronous dialers.
Because the default encapsulation is HDLC, you must explicitly configure LAPB encapsulation. To configure an interface to support LAPB encapsulation, perform the following task in interface configuration mode and also complete the DDR configuration of the interface:
| Task | Command |
|---|---|
| 1This command is documented in the "X.25 and LAPB Commands" chapter of the Router Products Command Reference publication. |
For more information about the serial connections on which LAPB encapsulation is appropriate, see the encapsulation lapb command in the "X.25 and LAPB Commands" chapter of the Router Products Command Reference publication.
For an example of configuring an interface for DDR over LAPB, see the "LAPB Support Configuration Example" section later in this chapter.
X.25 interfaces can now be configured to support DDR. Synchronous serial and ISDN interfaces on our routers can be configured for X.25 addresses, X.25 encapsulation, and mapping of protocol addresses to a remote host's X.25 address. In-band, DTR, and ISDN dialers can be configured to support X.25 encapsulation, but rotary groups cannot be configured to support X.25 encapsulation. On ISDN dialers configured for X.25 encapsulation, only one B channel can be used.
To configure an interface to support X.25, perform the following X.25-specific tasks in interface configuration mode and also complete the DDR configuration of the interface:
| Task | Command |
|---|---|
| Step 1. Configure the interface to use X.25 encapsulation. | |
| Step 2. Assign an X.25 address to the interface. | x25 address x.121-address11 |
| Step 3. Set up the LAN protocols-to-remote host address mapping. | x25 map protocol address [protocol2 address2 [...[protocol9 address9] x.121-address [option]1 |
| 1This command is documented in the "X.25 and LAPB Commands" chapter of the Router Products Command Reference publication. |
The order of DDR and X.25 configuration tasks is not critical; you can configure DDR before or after X.25, and you can even mix the DDR and X.25 commands.
For an example of configuring an interface for X.25 encapsulation and then completing the DDR configuration, see the section "X.25 Support Configuration Example."
Access to Frame Relay networks is now available through dial-up connections as well as leased lines. Dial-up connectivity allows Frame Relay networks to be extended to sites that do not generate enough traffic to justify leased lines and also allows a Frame Relay network to back up another network or point-to-point line.
DDR over Frame Relay is supported for synchronous serial and ISDN interfaces and for rotary groups, and is available for in-band, DTR, and ISDN dialers.
Frame Relay supports multiple connections (PVCs) over the same serial interface or ISDN B-channel, but only one physical interface can be used (dialed, connected, and active) in a rotary group or with ISDN.
The following restrictions apply to DDR over Frame Relay:
No new commands are required to support DDR over Frame Relay. In general, you configure Frame Relay and configure DDR. In general, complete the following steps to configure an interface for DDR over Frame Relay:
For example, enter the IP address and mask, the IPX network number, and the AppleTalk cable range and zone.
As a minimum, you must enable Frame Relay encapsulation and decide whether you need to do static or dynamic address mapping. If you decide to do dynamic mapping, you do not need to enter a command because Inverse ARP is enabled by default. If you decide to do static mapping, you must enter Frame Relay mapping commands.
You can then configure various options as needed for your Frame Relay network topology.
At a minimum, you must decide and configure the interface for outgoing calls only, incoming calls only, or both outgoing and incoming calls.
You can also configure DDR for your routed protocols (as specified in the "Configure DDR for Routed Protocols" section of this chapter) and for snapshot routing (as specified in the "Configure Snapshot Routing" section of this chapter). You can also customize DDR on your router (as described in the "Customize the DDR Network" section later in this chapter).
For examples of configuring various interfaces for DDR over Frame Relay, see the "Frame Relay Support Examples" section later in this chapter.
DDR supports the following routed protocols: AppleTalk, Banyan VINES, DECnet, IP, Novell IPX, ISO CLNS, and XNS.
To configure DDR for a routed protocol, perform the tasks in the relevant section:
To configure DDR for AppleTalk, you specify AppleTalk access lists and then define DDR dialer lists. Use the dialer-list protocol command to define permit or deny conditions for the entire protocol; for a finer granularity, use the dialer-list protocol command with the list keyword.
See the "Control Access to a DDR Interface" section for more information about defining dialer lists. For an example of configuring DDR for AppleTalk, see the "AppleTalk Configuration Example" section.
To configure DDR for Banyan VINES, perform one of the following tasks in global configuration mode:
| Task | Command |
|---|---|
vines access-list access-list-number {permit | deny} source source-mask vines access-list access-list-number {permit | deny} source source-mask [destination] [destination-mask] 1 |
| 1This command is documented in the "Banyan Vines Commands" chapter of the Router Products Command Reference publication. |
After you specify VINES standard or extended access lists, define DDR dialer lists as described in the "Control Access to a DDR Interface" section. Use the dialer-list protocol command to define permit or deny conditions for the entire protocol; for a finer granularity, use the dialer-list protocol command with the list keyword.
You can configure Banyan VINES on DDR synchronous and ISDN interfaces, as well as dialer rotary groups.
See the "Control Access to a DDR Interface" section for more information about defining dialer lists.
For an example of configuring Banyan VINES over DDR, see the "Banyan VINES Configuration Example" section.
To configure DDR for DECnet, perform one of the following tasks in global configuration mode:
| Task | Command |
|---|---|
access-list access-list-number {permit | deny} source source-mask access-list access-list-number {permit | deny} source source-mask [destination] [destination-mask]1 |
| 1This command is documented in the "DECnet Commands" chapter of the Router Products Command Reference publication. |
After you specify DECnet standard or extended access lists, define DDR dialer lists as described in the "Control Access to a DDR Interface" section. Use the dialer-list protocol command to define permit or deny conditions for the entire protocol; for a finer granularity, use the dialer-list protocol command with the list keyword.
DECnet control packets, including hello packets and routing updates, are classified using one or more of the following commands: dialer-list protocol decnet_router-L1 permit, dialer-list protocol decnet_router-L2 permit, and dialer-list protocol decnet_node permit.
You can configure DECnet on DDR synchronous and ISDN interfaces, and dialer rotary groups.
See the "Control Access to a DDR Interface" section for more information about defining dialer lists.
For an example of configuring DECnet over DDR, see the "DECnet Configuration Example" section in this chapter.
To configure DDR for IP, perform one of the following tasks in global configuration mode:
| 1This command is documented in the "IP Commands" chapter of the Router Products Command Reference publication. |
