Configuring ISDN BRI SPIDs

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Configuring ISDN BRI SPIDs

• A service profile identifier (SPID) is a number
  provided by the ISDN carrier to identify the line
  configuration of the BRI service.
• SPIDs allow multiple ISDN devices, such as voice
  and data, to share the local loop. SPIDs are
  required by DMS-100 and National ISDN-1 switches.

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Configuring ISDN BRI SPIDs

• Depending on the software version it runs, an
  ATT 5ESS switch might require SPIDs as well.

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Configuring ISDN BRI SPIDs

• Each SPID points to line setup and configuration
  information. When a device attempts to connect to
  the ISDN network, it performs a D channel Layer 2
  initialization process that causes a TEI to be
  assigned to the device. The device then attempts
  D channel Layer 3 initialization.

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Configuring ISDN BRI SPIDs

• If SPIDs are necessary but not configured or
  configured incorrectly on the device, the Layer 3
  initialization fails, and the ISDN services
  cannot be used.

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Configuring ISDN BRI SPIDs

• How are SPID numbers chosen? To keep SPID numbers
  simple (an oxymoron, it seems), most telcos use
  part of the ISDN phone number in the SPID naming
  system. Therefore, SPIDs are often the ISDN phone
  number with some optional numbers. For example,
  the SPID for the phone number [phone]
  could be 888555121200.

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Configuring ISDN BRI SPIDs

• A local directory number (LDN) might also be
  necessary if the router is to answer calls made
  to the second directory number. The commands to
  set SPIDs and LDNs on both B channels are as
  follows
• Router(config-if)isdn spid1 spid-number
  ldnRouter(config-if)isdn spid2 spid-number
  ldn.
• Your service provider will supply you with the
  necessary SPID configuration information.

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Configuring the Encapsulation Protocol

• Once DDR (or a user) creates an end-to-end path
  over the ISDN, some method of datagram
  encapsulation is needed for data to be
  transported. Available encapsulations for ISDN
  include
• PPP
• HDLC
• Frame Relay
• LAPB
• Combinet Proprietary Protocol (CPP)

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Configuring the Encapsulation Protocol

• LAPB can also be used for datagram delivery over
  the D channel.
• As noted earlier in this chapter, you will most
  likely use PPP as the Layer 2 encapsulation
  protocol.
• The encapsulation command is used to configure
  encapsulation for your ISDN interface
• Router(config-if)encapsulation ppp labp
  hdlc x25 cpp.

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Configuring the Encapsulation Protocol

• If you configure PPP encapsulation, you must use
  Password Authentication Protocol (PAP) or
  Challenge Handshake Authentication Protocol
  (CHAP) if you receive calls from more than one
  dial-up source. The following example represents
  a typical BRI encapsulation configuration using
  PPP with CHAP.

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Configuring the Encapsulation Protocol

• Router(config)interface bri 0Router(config-if)e
  ncapsulation pppRouter(config-if)ppp
  authentication chap.

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DDR

• With DDR, connections initiated by remote offices
  or telecommuters are brought up on an as-needed
  basis. This results in substantial cost savings
  for the company. In DDR scenarios, routers are
  not connected for long periods of time. Because
  ISDN provides greater throughput and quicker call
  setup than POTS, DDR is most often used with ISDN.

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DDR

• There are four basic steps to DDR configuration
  
• Define what constitutes interesting traffic by
  using the dialer-list command.
• Assign this traffic definition to an interface by
  using the dialer-group command.
• Define the destination address, hostname, and
  telephone number to dial by using the dialer map
  command.
• (Optional) Define call parameters by using other
  dialer commands such as dialer idle-timeout,
  dialer fast-idle, and dialer load-threshold.

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Defining Interesting Traffic

• The dialer-list command is used to define what
  type of traffic is "interesting." A router will
  bring up a DDR interface (if it's not up already)
  to route interesting traffic. Once the call is
  established, the router will not disconnect the
  call as long as it continues to receive
  interesting traffic to route over the DDR link.

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Defining Interesting Traffic

• While the link is up, other "uninteresting"
  traffic (traffic not defined by the dialer-list)
  can be routed over the link. However, if the link
  is idle for a configurable period of time, the
  router will disconnect the call.

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Defining Interesting Traffic

• The router considers the link idle if it is not
  being used to route interesting traffic. Every
  time interesting traffic is routed out a DDR
  interface the idle timer is reset. Therefore,
  traffic that is uninteresting will not keep a DDR
  call established.

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Defining Interesting Traffic

• The simpler form of the dialer-list command
  specifies whether a whole protocol suite, such as
  IP or IPX, will be permitted to trigger a call.
  The more complex form of the command references
  an access list, allowing finer control of the
  definition of interesting traffic.

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Defining Interesting Traffic

• Configure a simple dialer list using the
  following syntax
• Router(config)dialer-list dialer-group-number
  protocol protocol-name permit deny.
• The following example configures a dialer-list
  that will trigger a call for any IP traffic
• RTA(config)dialer-list 1 protocol ip permit.

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Defining Interesting Traffic

• The access-list command specifies interesting
  traffic that initiates a DDR call. The
  dialer-list command is used in conjunction with
  the access list

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Defining Interesting Traffic

• Router(config)access-list access-list-number
  permit deny protocol protocol-keywordsour
  ce source-wildcard anydestination
  destination-wildcard anyprotocol-specific-opti
  ons log
• Router(config)dialer-list dialer-group list
  access-list-number

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Defining Interesting Traffic

• The following example configures an access list
  and a dialer list so that only traffic from one
  host is considered interesting
• Router(config)access-list 24 permit host
  192.168.1.2 Router(config)dialer-list 1 list 24
  

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Assigning the Dialer-list to an Interface

• Once the dialer list is created, it needs to be
  assigned to the interface(s) responsible for
  initiating the call. This is accomplished by
  using the dialer-group command. You reference the
  dialer group in the dialer-list command, as
  shown
• Router(config)dialer-list 1 protocol ip
  permitRouter(config)interface bri
  0Router(config-if)dialer-group 1

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Assigning the Dialer-list to an Interface

• Note For a given protocol and a given dialer
  group, only one access-list can be specified in
  the dialer-list command.

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Dialer Map

• Once you define what constitutes interesting
  traffic, you must provide the interface
  responsible for initiating the call with all the
  parameters necessary to reach the destination.
• As you have seen in earlier chapters, the dialer
  map command identifies destination router
  information, such as the phone number to dial

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Dialer Map

• Router(config-if)dialer map protocol
  next-hop-address name hostname broadcast
  dial-string.

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Dialer Map

• Cisco IOS commands often contain the word "map,"
  which is used to statically map Layer 2 addresses
  to Layer 3 addresses. For example, the command
  frame-relay map is used to define a Layer 3
  next-hop-address to its Layer 2 address (DLCI
  number). With a dialer-map statement, you link a
  Layer 3 address (IP in this chapter) to a dial-up
  Layer 2 address (which, in this case, is a phone
  number).

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Dialer Map

• When setting up DDR between more than two sites,
  it is very important to use PPP authentication
  and to use the name keyword with the dialer map
  command. Dialer maps for inbound calls are maps
  between protocol addresses and authenticated user
  names.

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Optional Call Parameters

• The following additional call parameters can be
  added to the interface
• Router(config-if)dialer idle-timeout
  secondsRouter(config-if)dialer fast-idle
  secondsRouter(config-if)dialer load-threshold
  load outbound inbound either

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Use of Static and Default Routes

• In a DDR environment, dynamic routing can be a
  source of problems. Routing protocols such as RIP
  and OSPF rely on regular communication between
  link partners. If routers are connected via a
  dial-up link, active connections are usually
  intermittent.
• When using a dynamic routing protocol over DDR,
  you can configure a Cisco router for snapshot
  routing. This is optimized for use over
  intermittent links.

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Configuring Static Routes

• Static routes are entered manually, eliminating
  the need for a routing protocol to send routing
  updates across the DDR connection. Static routes
  can be effective in small networks that do not
  change often.

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Configuring Static Routes

• If a DDR router configured with the above static
  route receives an interesting packet destined for
  the 172.24.2.0 /24 network, the router would then
  look for a dialer map statement that maps a phone
  number to the next hop IP address, 10.2.3.2.

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Configuring Static Routes

• It is possible to use one route to define the
  next-hop IP address and a second to define the
  interface on which to find the next-hop (and
  dialer map). Thus, you may configure a static
  route using the local interface from which
  traffic must exit to reach the destination
  network (see Figure 3 ).

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Configuring Static and Default Routes

• As shown in Figure 3 , at least one static route
  pointing to the next-hop IP address is necessary
  for DDR to work.
• A default route is normally the only route needed
  on a remote network that has a single outside
  network connection. Networks that have only one
  path to the outside world are called stub
  networks. Most remote offices are stub networks,
  and are therefore often configured with a default
  route.

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Configuring Static and Default Routes

• To configure a static default route, use the ip
  route command
• Router(config)ip route 0.0.0.0 0.0.0.0
  next-hop-address exit-interface.
• On an IGRP router, you must use the ip
  default-network command if you want the router to
  include the default route in its updates. IGRP
  does not understand a route to 0.0.0.0/0.

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