3Com Router User Manual

							DCC Overview707
associate with multiple destination addresses. Each dialer interface can contain 
multiple physical interfaces. In addition, a physical interface does not necessarily 
belong to any dialer interface, and can directly route to one or multiple destination 
addresses.
As shown in Figure 224, physical interfaces Serial1, Bri0 and Serial2 belong to 
Dialer2, and on Dialer2 there are the maps of the string dialed and destination 
addresses.
Resource-Shared DCC
Compared to circular DCC, resource-shared DCC is simpler, and is more flexible due to 
the separation of logical and physical configurations. Specifically, resource-shared DCC 
has the following features:
■Separate the configuration of physical interfaces from the logical configuration 
required for calls and then dynamically binds them. Thus, a physical interface 
can provide services for various dial applications.
■A dialer interface only associates with a dialing destination address, which is 
specified in the 
dialer number command.
■Each logical dial (dialer) interface can use the services provided by multiple 
physical interfaces, and each physical interface can serve multiple dialer 
interfaces at the same time.
■Dial attributes are described based on RS-attributes set in implementing 
resource-shared DCC. All the calls originated to the same destination network 
use the same RS-attribute set (including the parameters like dialer interface, 
dialer bundle, physical interface).
■Resource-Shared DCC parameters cannot be directly configured on a physical 
interface. The physical interface can implement resource-shared DCC only after 
it is bound to a dialer interface.
■The figure below shows the association of the physical interfaces, dialer 
bundles and dialer interfaces in resource-shared DCC
Figure 225   Association of the physical interfaces, dialer bundles and dialer interfaces in 
Resource-Shared DCC
Dialer1
Dialer2
Destination A
Destination B
Destination C Physical
interfacesDialer
interfacesDialer3
Dialer
bundle3
Dialer
bundle2
Dialer
bundle1Serial0
Bri0
Serial1
Async0Bri1
Bri2dialer number
dialer number
dialer number 
						

							708CHAPTER 51: CONFIGURING DCC
As shown in Figure 225, a physical interface can belong to multiple dialer bundles 
and hence serve multiple dialer interfaces, but each dialer interface associates with 
only one destination address. Each dialer interface can use only one dialer bundle 
that contains multiple physical interfaces having different priorities.
In Figure 225, Dialer2 uses Dialer bundle2, and physical interfaces Bri0, Bri1 and 
Bri2 are members of Dialer bundle2. These physical interfaces have different 
priorities. Suppose that Bri0 in Dialer bundle2 is assigned with the priority 100, 
Bri1 with 50, and Bri2 with 75. Since the priority of Bri0 is higher than that of Bri1 
and Bri2, Bri0 will be selected first when Dialer2 selects a physical interface from 
Dialer bundle2.
DCC Features Available 
with 3Com Routers3Com routers provide flexible and practical dial interface solutions, as described in 
the following sections.
Basic DCC features
Basic DCC features include support for:
■Multiple dial interfaces, such as synchronous/asynchronous serial interface, 
AUX port, ISDN BRI or PRI interface, and AM interface. The user can flexibly 
combine them, depending on the actual networking and network topology.
■Link layer protocols, such as PPP and Frame Relay, on dial interfaces (physical or 
dialer interfaces)
■Network layer protocols, such as IP, IPX and Bridge on dial interfaces.
■Dynamic routing protocols, such as RIP and OSPF, on dial interfaces.
■Flexible dial interface standby modes
■Modem control on asynchronous dial interfaces for managing various modems.
Implementing callback through DCC
In callback, the “called party” originates a return call to the “calling party”. In this 
case, the calling party is the client, and the called party is the server. The callback 
client originates a call first, and the callback server determines whether to 
originate a return call. If a callback is needed, the server immediately disconnects 
and originates a return call.
DCC callback can bring the following advantages:
■Enhances security: When placing a return call, the server dials the calling 
number configured at the local end. Hence, the insecurity resulted from the 
distribution of user name and password can be avoided.
■Changes the charge bearer. This is useful for saving cost if the call rates in two 
directions are different.
■Consolidates the call charge bills, which facilitates the settlement.
3Com routers provide the PPP callback and ISDN caller identification callback 
features. The PPP callback conforms to and can be adopted to a RFC1570 system 
regardless of whether the client and server own fixed network addresses, or that 
the client accepts the network address that is dynamically assigned. 
						

							Configuring DCC 709
Preparing to Configure 
DCCDetermine the topology of DCC application
■Determine which routers will provide DCC and the relevant communication 
parameters between the routers.
■Determine the interfaces on the routers that provide DCC the functions carried 
out by each router.
■Determine the transmission medium, PSTN or ISDN. 
Prepare the data for DCC configuration
■Identify the interface type (synchronous/asynchronous serial interface, ISDN BRI 
or PRI interface, AM interface, AUX interface) and configures the basic physical 
parameters on the interface.
■Configure the link layer protocol (PPP, HDLC, Frame Relay or other modes) to 
be used on the dial interface.
■Configure the network protocol (IP, IPX) to be used on the dial interface.
■Configure the routing protocol (RIP, OSPF, or other protocols) to be supported 
on the dial interface.
■Select a DCC configuration method (circular DCC or resource-shared DCC).
Configure the local parameters of DCC
Follow the configuration procedure to configure the basic DCC parameters 
according to the selected DCC configuration method, (circular DCC or 
resource-shared DCC) to enable the initial DCC implementation. Configure MP 
binding, PPP callback, ISDN caller identification callback, ISDN leased line, 
auto-dial, or a combination of these, in addition to the basic DCC configuration, if 
special applications are required. Alternatively, depending on the actual dialing link 
state the user can make an appropriate adjustments to the attribute parameters of 
the DCC dial interface.
Configuring DCC Configuring DCC includes tasks that are described in the following sections:
■Configuring DCC Prepared Parameters
■Configuring Circular DCC
■Configuring Resource-Shared DCC
■Configuring MP Binding for DCC
■Configuring PPP Callback
■Configuring ISDN Caller Identification Callback
■Configuring Special DCC Functions
■Configuring Attributes of DCC Dial Interface
Configuring DCC 
Prepared ParametersRegardless of which method is used, circular DCC or resource-shared DCC, the 
following two basic DCC configuration tasks should be performed:
■Configuring the mode of the physical interface
■Configuring link layer and network and routing protocols on the interface 
						

							710CHAPTER 51: CONFIGURING DCC
Configuring the mode of the physical interface
For a synchronous/asynchronous serial interface, configure the physical interface 
to operate in asynchronous and dial mode if it is connected to an asynchronous 
modem. If the physical interface is connected to a synchronous modem, configure 
the physical interface to operate in synchronous and dial mode. For an ISDN BRI or 
PRI interface, this step can be ignored.
Perform the following configuration in dial interface (synchronous/asynchronous 
serial interface) view.
Ta b l e 742   Configure Physical Interface Mode
By default, a synchronous/asynchronous serial interface works in synchronous 
mode and an asynchronous serial interface works in dial (modem) mode.
There is no need to configure the physical-mode command for the synchronous 
serial interface connected to a synchronous modem. The user only needs to 
configure the modem command for an AUX interface.
Configuring link layer and network and routing protocols on the interface
Set the link layer protocol in dial interface (physical or dialer interface) view 
through the 
link-protocol command, configure an IP or IPX address for the dial 
interface through the
 ip address or ipx network command, and perform other 
configurations in system view.
Ta b l e 743   Configure Link Layer and Network and Routing Protocols on the Interface
The linklayer-protocol-type can be SLIP, PPP or Frame Relay. For configuration 
details, see the related section in Operation Manual - Link Layer Protocol, 
Operation Manual - Network Protocol and Operation Manual - Routing Protocol.
For a dialer interface adopting Resource-Shared DCC to implement Frame Relay 
over ISDN, the B channel is encapsulated with PPP originally. Once the B channel is 
ready for communication, the protocol encapsulated on the interface dynamically 
OperationCommand
Configure a synchronous/asynchronous 
serial interface to work in asynchronous or 
synchronous modephysical-mode { async | sync }
Configure the asynchronous serial 
interface to work in dial modemodem [ in | out | auto-answer ]
OperationCommand
Set a link layer protocol on the dial 
interfacelink-protocol 
linklayer-protocol-type
Configure an IP address for the dial 
interfaceip address ipaddress mask
Activate IPXipx enable ipx-address
Configure an IPX address for the dial 
interfaceipx network network-number
Configure IPX static routeipx route network.node tick ticks hop 
hops [ preference value]
Configure RIP route protocol rip 
Configure OSPF route protocol ospf [ enable ]
Configure BGP route protocol bgp  as-number 
						

							Configuring DCC 711
becomes the same as that on the Dialer interface, which allows the same B 
channel to be used by different link layer protocols, improving flexibility. When the 
B channel is disconnected, the encapsulation protocol on the ISDN interface will 
be automatically restored to PPP.
Associating a DCC dialer ACL with the interface
A properly configured dialer ACL can filter various packets that traverse the dial 
interface. The packets fall into two categories, depending on whether the packets 
are in compliance with the “permit” or “deny” statements in the dialer ACL.
■The packet complies with the “permit” statements. If the corresponding link 
has been set up, DCC will send the packet through this link and clear all the 
data in the idle-timeout timer. If not, it originates a new call.
■The packet does not comply with the “permit” statements in the list. If the 
corresponding link has been set up, DCC will send the packet by this link 
without clearing the idle-timeout timer to zero. If not, it will discard the packet 
without originating a call.
To enable DCC to originate a call normally, the user must configure a DCC dialer 
ACL and associate the corresponding interface (physical or dialer interface) to the 
dialer ACL through the 
dialer-group command. Otherwise, DCC cannot 
normally renominate a call. The user can either directly configure the conditions 
for filtering packets in the DCC dialer ACL, or reference the filtering rules in an 
ACL.
Perform the configuration of the dialer-group command in dial interface 
(physical or dialer interface) and other configurations in system view.
Ta b l e 744   Configure Physical Interface Mode
By default, neither DCC dialer ACL, nor the access control group assigned with a 
dial interface is configured.
OperationCommand
Configure a DCC dialer ACLdialer-rule dialer-group { 
protocol-name { permit | deny } | acl 
acl-number }
Delete the DCC dialer ACLundo dialer-rule dialer-group
Configure a access control group for the 
dial interfacedialer-group dialer-group
Remove the dial interface from the 
specified access control groupundo dialer-group
Create and enter a ACL acl acl-number
Configure a standard ACLrule [ normal | special ] { deny | 
permit } source { any | source-addr [ 
source-wildcard-mask ] }
Configure an extended ACLrule [ normal | special ] { deny | 
permit } { tcp | udp }  source { any 
| source-addr source-wildcard-mask } 
source-port [ operator port-number ] 
destination { any | destination-addr 
destination-wildcard-mask } 
destination-port [ operator 
port-number ] [ log ] 
						

							712CHAPTER 51: CONFIGURING DCC
Assure that the commands dialer rule dialer-group and dialer-group 
dialer-group adopt the same dialer-group.
Do not concurrently configure the functional arguments of the protocol-name and 
acl-number for the same 
dialer rule command when configuring a dialer ACL. 
Configuring Circular DCCIf Circular DCC is used, each physical interface can either be directly configured 
with the DCC parameters, or bound to a dialer interface to inherit the DCC 
parameters through a dialer circular group. Between these two options, 
configuring the DCC parameters directly on a physical interface is only applicable 
for a single interface to originate calls to one or more remote ends. However, a 
dialer circular group is also applicable for multiple interfaces to originate calls to 
one or more remote ends in addition to that.
Dialer circular group associates a dialer interface with a group of physical 
interfaces. The DCC configuration of this dialer interface are automatically 
inherited by all the physical interfaces in the dialer circular group. After 
configuring the parameters for the dialer circular group, any physical interface in 
the group can call any predefined destination if the dialer interface is associated 
with multiple destinations.
Depending on the network topology and DCC dialing demands, such as one 
interface or multiple interfaces can both originate and receive calls, the user can 
flexibly use one configuration or the combination of several configurations in the 
Circular DCC configurations introduced below.
In the circular DCC implementation of DCC, the two dial parties can configure 
Password Authentication Protocol (PAP) or Challenge-Handshake Authentication 
Protocol (CHAP) authentication. However, the other party must configure 
authentication if one party has done that. For security of the dialing ID, you should 
configure authentication in actual networking applications. For configuration 
methods, see the section in Operation Manual - Link Layer Protocol and note the 
following items at the same time:
■At the sending side, if DCC is directly enabled on the physical interface, directly 
configure PAP or CHAP authentication on the physical interface. If DCC is 
enabled through a dialer circular group, configure PAP or CHAP authentication 
on the dialer interface.
■When configuring PAP or CHAP authentication at the receiving end, the user is 
recommended to make the configuration on both physical and dialer 
interfaces. That is because the physical interface will first implement PPP 
negotiation and authenticate the validity of the dialing user when receiving a 
DCC call request, and then deliver the call to the upper layer DCC module for 
processing.
Configuring an interface to originate calls to a remote end
Perform the following configuration steps after the basic DCC configuration is 
completed. As shown in 
Figure 226, a local interface originates a call to a single 
remote end. 
						

							Configuring DCC 713
Figure 226   An interface placing a call to a remote end
As shown in this figure, the single local interface interface0 (if0) originates a DCC 
call to the single remote interface if1. Since the call originates at a single remote 
end the dialer string can be configured using the dialer number or dialer route 
command. When the call originates from the single interface at the local end, the 
dialer circular group can be used to configure the DCC. The user can choose to 
configure either PAP or CHAP authentication on the interface.
Perform the following configuration in dial interface (physical or dialer interface) 
view. 
Ta b l e 745   Configure a Local Interface to Originate Calls to a Remote End
By default, Circular DCC is enabled on ISDN BRI and PRI interfaces, but disabled on 
other interfaces (serial, asynchronous, AUX, etc.) and the user should manually 
configure the 
dialer enable-circular command. No dialer number for calling 
the remote end is configured by default.
Configure an interface to receive calls from a remote end
Perform the following configuration steps after the basic DCC configuration is 
implemented. As shown in the following figure, a local interface receives a call 
from a single remote end (the picture components of inverse color represent the 
routers irrelevant with the networking):
Figure 227   An interface receiving a call from a remote end
OperationCommand
Enable Circular DCCdialer enable-circular
Configure a dialer number for calling a 
remote enddialer number [ dial-number ]
Delete the dialer number for calling the 
remote endundo dialer number
Local end
(Single interface)if0if1Remote end
(Single interface)
Local end
(Single interface)Remote end A
(Single interface)
Router if0if1
Router 
						

							714CHAPTER 51: CONFIGURING DCC
As shown in this figure, the single local interface interface0 (if0) receives a DCC 
call from a single remote interface if1. Since the call is received by a single local 
interface, the dialer circular group can be used to configure DCC. You can choose 
to configure either PAP or CHAP authentication.
Perform the following configuration in dial interface (physical or dialer interface) 
view.
Ta b l e 746   Configure a local interface to receive calls from a remote interface
By default, Circular DCC is enabled on ISDN BRI and PRI interfaces, but disabled on 
other interfaces (serial, asynchronous, AUX, etc.) and you should manually 
configure the 
dialer enable-circular command. 
Configuring originating calls from an interface to multiple remote ends
Perform the following configuration steps after the basic DCC configuration is 
implemented. As shown in 
Figure 228, a local interface originates calls to multiple 
remote ends (the picture components of inverse color represent the routers 
irrelevant with the specific networking):
Figure 228   An interface placing calls to multiple remote ends
As shown in the above figure, a single local interface interface0 (if0) originates 
DCC calls to the remote interfaces if1 and if2. Since calls are originated to multiple 
remote ends, the user must use the 
dialer route command to configure the 
dialer numbers and destination addresses. Since the calls originate from a single 
local interface, the dialer circular group can be used to configure DCC. The user 
can select to configure either PAP or CHAP authentication.
Perform the following configuration in dial interface (physical or dialer interface) 
view.
Ta b l e 747   Configure a Local Interface to Originate Calls to Multiple Remote Ends
OperationCommand
Enable Circular DCCdialer enable-circular
OperationCommand
Enable Circular DCCdialer enable-circular
Configure destination address(es) and 
dialer number(s) for calling one or more 
remote endsdialer route protocol 
next-hop-address dial-number
Router
Remote end C
Single/Multiple interface(s) Local end
(Single interface)Remote end B
Single/Multiple interface(s)Remote end A
Single/Multiple interface(s)
if0if1
if2
if3
Router
Router
Router 
						

							Configuring DCC 715
By default, Circular DCC is enabled on ISDN BRI and PRI interfaces, but disabled on 
other interfaces (serial, asynchronous, AUX, etc.) and the user should manually 
configure the 
dialer enable-circular command. No dialer numbers for calling 
the remote ends are configured by default.
Configuring an interface to receive calls from multiple remote ends
Perform the following configuration steps after the basic DCC configuration is 
implemented. As shown in 
Figure 229, a local interface receives calls from multiple 
remote ends.
Figure 229   An interface receiving calls from multiple remote ends
As shown in this figure, the single local interface interface0 (if0) receives DCC calls 
from the remote interfaces if1 and if4. Since the local end is a single interface, the 
dialer circular group can be used to configure DCC. The user can select to 
configure either PAP or CHAP authentication.
Use the local-user password command to set up the user name and password 
to allow for dial in the system view, and then perform other configuration steps in 
the dial interface (physical or dialer interface) view.
Ta b l e 748   Configure a Local Interface to Receive Calls from Multiple Remote Ends
By default, circular DCC is enabled on ISDN BRI and PRI interfaces, but disabled on 
other interfaces (serial, asynchronous, AUX, etc.) and the user should manually 
configure the 
dialer enable-circular command. No authentication 
parameters or dial-in user information are configured by default.
Configuring multiple interfaces to originate calls to multiple remote ends
Perform the following configuration steps after the basic DCC configuration is 
implemented. As shown in the following figure, multiple local interfaces originate 
calls to multiple remote ends (the picture components of inverse color represent 
the routers irrelevant with the networking):
Delete the destination address(es) and 
dialer number(s) for calling one or more 
remote endsundo dialer route protocol 
next-hop-address
OperationCommand
Enable Circular DCCdialer enable-circular
Local end
(Single interface)Remote end B
Single/Multiple interface(s)Remote end A
Single/Multiple interface(s)
Remote end C
Single/Multiple interface(s) if0if1
if2
if4if3
Router
Router
Router
Router 
						

							716CHAPTER 51: CONFIGURING DCC
Figure 230   Multiple interfaces placing calls to multiple remote ends
As shown in Figure 230, the local interfaces interface0 (if0), if1, and if2 originate 
DCC calls to the remote interfaces if1, if2 and if3. For allowing calls to originate 
from multiple remote ends, the user must use the 
dialer route command to 
configure the dialer strings and destination addresses. For the calls to originate 
from multiple interfaces, the dialer circular group must be used to configure DCC. 
The user can select to configure either PAP or CHAP authentication.
Instead of using their own IP addresses, the physical interfaces in the dialer circular 
group will use the IP address of the dialer interface in making the calls. The 
argument number of the 
dialer circular-group number command configured 
in physical interface view must be the same as the number used in the 
interface 
dialer number
 command configured in the view of the dialer interface to 
properly associate the physical interface. ISDN BRI or PRI interface is regarded as 
the dialer circular group for the B channels connected through either of these 
interfaces. At the same time, they can be regarded as the physical interfaces by 
other dialer circular groups.
Use the interface dialer command to create a dialer interface in global view, 
add it to the specified dialer circular group through the 
dialer circular-group 
command, and perform other configuration processes in dialer interface view.
Ta b l e 749   Configure Multiple Local Interfaces to Originate Calls to Multiple Remote Ends
OperationCommand
Enable Circular DCCdialer enable-circular
Configure the destination address(es) and 
the dialer number(s) for calling one (or 
more) remote end(s).dialer route protocol 
next-hop-address dial-number 
Delete the destination address(es) and 
dialer number(s) for calling one (or more) 
remote ends.undo dialer route protocol 
next-hop-address
Create a dialer interface and enter the 
dialer interface view.interface dialer number
Delete the existing configurations of the 
dialer interfaceundo interface dialer number
Bundle a physical interface with the 
specified dialer circular groupdialer circular-group number
Remove the physical interface from the 
specified dialer circular groupundo dialer circular-group
Configure the priority of the physical 
interface in the dialer circular group.dialer priority priority
Restore the default priority of the physical 
interface in the dialer circular group.undo dialer priority
Router
Remote end C
Single/Multiple interface(s) Local end
(Multiple interfaces)Remote end B
Single/Multiple interface(s)Remote end A
Single/Multiple interface(s)
if0
if1
if2if1
if2
if3
Router
Router
Router