3Com Router User Manual

							Configure X.25217
DCE equipment in X.25 networks to provide the function of load balancing for 
DTE equipment) then configuration of X.25 load balancing needs to be made on 
the routers.
The main configuration tasks of X.25 load balancing are as follows:
■Start X.25 switching
■Create X.25 hunt group
■Add interfaces and XOT Tunnels to hunt group
■Configure the X.25 switching route whose forward address is hunt group
■Configure other X.25 switching routes 
Hunt group addresses do not need separate configuration. Only the destination 
addresses need to be set as hunt group addresses on source DTEs.
1Start X.25 switching
Perform the following configuration in system view.
Ta b l e 260   Start /Close X.25 switching function
2Create X.25 hunt group
Perform the following configuration in system view.
Ta b l e 261   Create/Delete X.25 hunt group
3Add interfaces and XOT Tunnels to hunt group
Perform the following configuration in X.25 hunt group view.
Ta b l e 262   Add/Delete interfaces or XOT Tunnels in hunt group
It should be noted that a hunt group can have ten synchronous serial interfaces or 
XOT Tunnels at most. XOT Tunnels cannot be added to the hunt group that adopts 
vc-number channel selection policy.
4Configure X.25 switching route which is forwarded to hunt group
Perform the following configuration in system view.
OperationCommand
Start X.25 switchingx25 switching
Close X. 25 switchingundo x25 switching
OperationCommand
Create X.25 hunt groupx25 hunt-group hunt-group-name { 
round-robin | vc-number }
Delete X.25 hunt groupundo x25 hunt-group hunt-group-name
OperationCommand
Add interfaces to hunt groupchannel interface interface-type 
interface-number
Delete specified interfaces from hunt 
groupundo channel interface 
interface-type interface-number
Add XOT Tunnels to hunt groupchannel xot ip-address
Delete specified XOT Tunnels from hunt 
groupundo channel xot ip-address 
						

							218CHAPTER 16: CONFIGURING LAPB AND X.25
Ta b l e 263   Add/Delete X.25 switching route whose forwarding address is hunt group
5Configure other X.25 switching routes
Ta b l e 264   Add/delete other X.25 switching routes
Configure X.25 over 
Other Protocols
Configure X.25 over TCP 
(XOT)Introduction to XOT Protocol
XOT (X.25 Over TCP) is a protocol that is supported by TCP, and implements the 
connection of two X.25 networks through IP network. The practical application 
environment is shown in the following figure.
Figure 66   XOT typical application diagram
Since the application of IP network is broader and broader, the practical 
applications of supporting X.25 data through IP net and connecting X.25 
networks are becoming more and more. The conventional X.25 protocol is the 
third layer of the OSI seven-layer model, i.e., the network layer, for which the LAPB 
OperationCommand
Add an X.25 switching route whose 
forwarding address is hunt groupx25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] 
hunt-group hunt-group-name
Delete an X.25 switching route whose 
forwarding address is hunt groupundo x25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] [ 
hunt-group hunt-group-name ]
OperationCommand
Add an X.25 switching route whose 
forwarding address is interfacex25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] interface 
serial interface-number
Delete an X.25 switching route whose 
forwarding address is interfaceundo x25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] [ 
interface serial interface-number ]
Add an X.25 switching route whose 
forwarding address is XOT Tunnelx25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] xot 
ip-address1 [ ip-address2 ] … [ 
ip-address6 ] [ xot-option ]
Delete an X.25 switching route whose 
forwarding address is XOT Tunnelundo x25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] [ xot 
ip-address1 [ ip-address2 ] … [ 
ip-address6 ] ] [ xot-option ]
X.25IPX.25
Router A
Router BRouter C
Router D 
						

							Configure X.25 over Other Protocols219
protocol provides reliable data transmission link. Because TCP has the mechanism 
of error redirection and window flow controlling to guarantee the reliability of 
links, it can be used by X.25. XOT builds a TCP tunnel connection between the 
two X.25 networks, and the X.25 packets are supported by TCP as data of 
application layer, i.e., TCP serves as the “link layer” of X.25. You can regard the 
middle RouterB, RouterC and IP net as a big “X.25 switch”, and data is directly 
switched from RouterA to RouterD through this “switch”.
The XOT features implemented in the 3Com Router accords with RFC1613 
recommendation, and it possess the following features:
■Supporting SVC application. The two routers can dynamically set up a SVC by 
sending call packet, and the VC will automatically be cleared when no data is 
transmitted.
■Supporting PVC application. After the two routers configure a PVC, they 
directly enter the data transmission status without the process of call 
establishing. If no data is transmitted, this VC will not be cleared automatically.
■Supporting the Keepalive attribute of TCP. If Keepalive is not configured, TCP 
connection will not be cleared after a long period of time when the line is 
disconnected. If Keepalive is configured, TCP check the usability of the links in 
time, and it will automatically clear the TCP connection if it does not receive 
the answer of the opposite side for certain times.
Implementing theory of XOT (taking SVC as an example):
As shown in the former figure, when it has data to transmit, RouterA first send a 
request packet to set up a VC. After RouterB receive the call packet and judges 
that it is XOT application, it first set up a TCP connection with RouterC, and then 
stick the XOT packet header to X.25 call packet which is encapsulated in TCP 
header to send to RouterC. RouterC takes off the TCP and XOT packet headers 
and send the call request packet to RouterD through X.25 local switch. After 
RouterD receives the call request packet, it answers the call to confirm until the 
link is completely set up and enters the data transmission status. To RouterA and 
RouterD, the whole process of setting up and applying TCP connection is 
transparent, and they do not and cannot care whether the data is forwarded 
through IP net or X.25 net.
Configure XOT
XOT configuration includes:
■Start X.25 switching
■Configure IP side interface
■Configure local switching (SVC)
■Configure XOT route
■Configure Keepalive and xot-source attributes
■Start X.25 switching
Because the XOT is the extension of X.25 switch, first you have to start X.25 
switch.
Perform the following tasks in system view. 
						

							220CHAPTER 16: CONFIGURING LAPB AND X.25
Ta b l e 265   Start X.25 switching
1By default, do not start X.25 switch.
2Configure IP side interface
Because the XOT implements the connection of two X.25 nets through IP net, first 
you should ensure that the IP net is expedite. For the specific configuration, refer 
to chapters of Operation Manual - Network protocol.
3Configure local switching (SVC)
For SVC, when it receives the packets from the remote side, it must send out the 
packets through local switch interface, so you have to configure local switching.
The following commands determine: In SVC, through which switch interface the 
packets getting to local side will be sent out. 
Perform the following tasks in system view.
Ta b l e 266   Configure local switching
4Configure XOT route
The following configuration determines how the X.25 side packets received are 
forwarded through IP net. There are different views for SVC and PVC.
For SVC, perform the following tasks in system view.
Ta b l e 267   Configure SVC XOT switching
The local X.25 route must be configured in the SVC mode.
For PVC, perform the following tasks in interface view.
OperationCommand
Enable X.25 switchingx25 switching
OperationCommand
Configure X.25 local switchingx25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] interface 
serial interface-number
Delete X.25 local switchingundo x25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] [ 
interface serial interface-number ]
OperationCommand
Configure a SVC XOT routex25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] xot 
ip-address1 [ ip-address2 ] … [ 
ip-address6 ] [ xot-option ]
Delete a SVC XOT routeundo x25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] [ xot 
ip-address1 [ ip-address2 ] … [ 
ip-address6 ] ] [ xot-option ] 
						

							Configure X.25 over Other Protocols221
Ta b l e 268   Configure PVC XOT switching
5Configure Keepalive and xot-source attributes
After the TCP link is established, TCP will not be easily cleared even if the link is 
disconnected. But after configuring Keepalive, the router will send checking 
packets in time to check the usability of the link. If it cannot get confirmation after 
sending out packets several times, it will consider the link failure and clear it 
automatically.
Ta b l e 269   Configure Keepalive and xot-source attributes
Configure X.25 over 
Frame Relay (Annex G)Configure Annex G Data Interoperation
ANSI T1.617 Annex G defines how to transmit X.25 packets over Frame Relay 
DCLIs. With the integrated acknowledgement, retransmission and flow control 
mechanisms of X.25, Annex G DLCI can provide reliable transmission service, as 
well as interconnect X.25 networks via Frame Relay networks. Annex G is a 
stopgap between X.25 network and Frame Relay network, which can effectively 
protect the investment that the user has made.
This section covers how to make configurations so that Annex G DLCI can be used 
to transmit IP data. For the configurations of X.25 switching over Annex G DLCIs, 
refer to the subsequent section.
Ta b l e 270   Configure an Annex G DLCI
Annex G DLCI does not support IARP (Inverse Address Resolution Protocol), so the 
user should configure a static map between the destination IP address and the 
Frame Relay address.
OperationCommand
Add a PVC XOT routex25 xot pvc pvc-number ip address 
interface type number
Delete a PVC XOT routeundo x25 xot pvc pvc-number
OperationCommand
Configure SVC Keepalive and 
xot-source attributesx25 switch svc x.121-address [ sub-dest 
destination-address ] [ sub-source 
source-address ] xot ip-address1 [ 
ip-address2 ] … [ ip-address6 ] [ 
xot-option ]
Configure PVC Keepalive and 
xot-source attributesundo x25 switch svc x.121-address [ 
sub-dest destination-address ] [ 
sub-source source-address ] [ xot 
ip-address1 [ ip-address2 ] … [ 
ip-address6 ] ] [ xot-option ]
OperationCommand
Configure a Frame Relay interfacelink-protocol fr
Configure an IP address for the interfaceip address { A.B.C.D } { A.B.C.D }
Configure a Frame Relay DLCIfr dlci dlci-number
Configure the Frame Relay DLCI to be Annex 
G DLCIannexg { dce | dte }
Map the Frame Relay address to the 
destination IP addressfr map ip { A.B.C.D } { 
dlci-number } 
						

							222CHAPTER 16: CONFIGURING LAPB AND X.25
When configuring an Annex G DLCI, the user must explicitly configure it with the 
argument DCE or DTE. In addition, the configurations on the routers of a 
connection should not be the same. That is, if a router is configured to work as 
DTE, the other router must be configured as DCE.
Ta b l e 271   Configure the X.25 attributes for an Annex G DLCI
It is necessary to properly understand the differences between the Frame Relay 
address map configured in interface view and the X.25 address map configured in 
X.25 template view. The former specifies the DLCI from which the packets 
destined to an IP address can be sent, whereas the latter specifies the X.25 address 
to which the packets must originate X.25 calls in order to reach the destination IP 
address. IP packets can be properly sent and received on the Annex G DLCI only if 
the two address maps are configured.
The LAPB/X.25 attributes configured in an X.25 template and those configured on 
an X.25 interface are similar. To ensure that an X.25 call can be set up, the 
configurations on the routers of a connection should keep in consistency. 
1Configure the X.25 Attributes for a DLCI
Frame Relay is mainly applied to data transmission. However, it does not provide 
acknowledgement mechanism or error correction function. In other words, 
transmission over Frame Relay networks is unreliable. To ensure reliable 
transmission of signals for call set up and termination in dynamic calling mode, 
these signals are transmitted over an X.25 VC (Virtual Circuit). Thereby, reliable 
transmission can be ensured through the X.25 message acknowledgement 
mechanism. A DLCI needs to be configured with X.25 attributes only when VoFR 
(Voice over Frame Relay) adopts dynamic calling mode.
The x.25 template command is performed in system view. Creating an X.25 
template will enter x.25 template mode at the same time. Perform the commands 
x25 and lapb in x.25 template mode, and x25-template in interface DLCI mode.
Ta b l e 272   Configure the X.25 attributes for an DLCI
OperationCommand
Create an X.25 templatex25 template { name }
Configure the local X.25 address in the X.25 
templatex25 x121-address  x.121 address 
Map the destination X.25 address to the 
destination IP address in the X.25 templatex25 map ip { A.B.C.D } { 
x121-address x.121 address }
Configure other LAPB/X.25 parameters in the 
X.25 templateFor details, refer to the 
LAPB/X.25 configuration commands.
Associate the parameters configured in the 
X.25 template to an Annex G DLCIx25-template { name }
OperationCommand
Create an X.25 templatex25 template name
Delete the X.25 templateno x25 template name
Configure the X.25 attributesx25
Restore the X.25 attributes to default settingsno x25
Configure the LAPB attributeslapb
Restore the LAPB attributes to default 
settingsno lapb
Associate the X.25 template with a DLCIx25-template name
Remove the association between the X.25 
template and the DLCIno x25-template 
						

							Display and Debug LAPB and X.25223
By default, X.25 template is not applied on DLCIs.
Display and Debug 
LAPB and X.25In the all views, perform the following tasks to enable real-time monitoring of the 
current status of LAPB and X.25.
Ta b l e 273   Display and debug LAPB and X.25
Ty p i c a l  L A P B  
Configuration 
ExampleI. Networking Requirement
Two routers are directly connected via serial ports with LABP protocol to transmit 
IP data packets directly.
II. Networking Diagram
Figure 67   Direct connection between two routers via serial ports
III. Configuration Procedure
As shown in the diagram above, perform the following configuration tasks:
1Configure Router A:
aSelect interface
[Router]interface serial 0
bSpecify IP address for this interface
[Router-Serial0]ip address 202.38.160.1 255.255.255.0
cConfigure the link layer protocol of the interface to LAPB and specify its 
working mode as DTE
[Router-Serial0]link-protocol lapb dte
dConfigure other Lapb parameters (if the link is of good quality, and a higher 
rate is required, the flow control parameter modulo can be increased to 128, k 
to 127, but they must be the same for both ends in the direct connection)
OperationCommand
Display interface informationdisplay interface [ type number ]
Display X.25 alias tabledisplay x25 alias-policy
Display X.25 hunt group informationdisplay x25 hunt-group-info [ 
hunt-group-name ]
Display X.25 address mapping tabledisplay x25 map
Display X.25 switching route tabledisplay x25 switch- vc-table svc
Display X.25 switching virtual circuit tabledisplay x25 switch-vc-table pvc
Display X.25 virtual circuit display x25 vc lci-number
Enable X.25 information debugging debugging x25 all [interface 
interface-type interface-number ] 
Enable X.25 event debugging debugging x25 event [interface 
interface-type interface-number ]
Enable X.25 packet debugging debugging x25 packet [interface 
interface-type interface-number ]
Enable XOT debugging debugging x25 xot
V.35 cable
Serial 0
Serial 1
Router A
Router B 
						

							224CHAPTER 16: CONFIGURING LAPB AND X.25
[Router-Serial0]lapb module 128
[Router-Serial0]lapb window-size 127
2Configure Router B:
aSelect interface
[Router]configure
[Router]interface serial 1
bSpecify IP address for this interface
[Router-Serial1]ip address 202.38.160.2 255.255.255.0
cConfigure the link layer protocol of the interface to LAPB and specify its 
working mode as DCE
[Router-Serial1]link-protocol lapb dce
dConfigure other LAPB parameters (if the link quality is good, and a higher rate 
is required, the flow control parameter modulo can be increased to 128, k to 
127, but they must be the same for both ends in the direct connection)
[Router-Serial1]lapb modulo 128
[Router-Serial1]lapb window-size 127
Ty p i c a l  X . 2 5  
Configuration 
Example
Back to Back Direct 
Connection of Two 
Routers via Serial 
InterfaceI. Networking Requirement
As shown in the diagram below, two routers are to be directly connected back to 
back; the X.25 protocol is used between the serial ports for IP data packet 
transmission.
II. Networking Diagram
Figure 68   Direct connection of two routers via serial ports
III. Configuration Procedure
1Configure Router A:
aSelect interface
[Router]interface serial 0
bSpecify IP address for this interface
[Router-Serial0]ip address 202.38.160.1 255.255.255.0
cConfigure the link layer protocol of the interface to X.25 and specify its 
working mode as DTE
[Router-Serial0]link-protocol x25 dte
dSpecify X.121 address of this interface
[Router-Serial0]x25 x121-address 20112451
V.24/V.35 cable
Router ASerial 1
Serial 0
Router B 
						

							Typical X.25 Configuration Example225
eSpecify address mapping to the peer
[Router-Serial0]x25 map ip 202.38.160.2 x121-address 20112452
fAs this is a direct connection, the flow control parameters can be increased 
slightly
[Router-Serial0]x25 packet-size 1024 1024
[Router-Serial0]x25 window-size
2Configure Router B:
aSelect interface
[Router]interface serial 1
bSpecify IP address for this interface
[Router-Serial1]ip address 202.38.160.2 255.255.255.0
cConfigure the link layer protocol of the interface to X.25 and specify its 
working mode as DCE
[Router-Serial1]link-protocol x25 dce
dSpecify X.121 address of this interface
[Router-Serial1]x25 x121-address 20112452
eSpecify address mapping to the peer
[Router-Serial1]x25 map ip 202.38.160.1 x121-address 20112451
fAs this is a direct connection, the flow control parameters can be increased 
slightly
[Router-Serial1]x25 packet-size 1024 1024
[Router-Serial1]x25 window-size 5 5
Connect the Router to 
X.25 Public Packet 
NetworkI. Networking Requirement
As shown in the diagram below, three routers A, B and C are connected to the 
same X.25 network for mutual communication. The requirements are:
■IP addresses of the interfaces Serial0 of three routers are 168.173.24.1, 
168.173.24.2 and 168.173.24.3 respectively.
■X.121 addresses assigned to the three routers by the network are 30561001, 
30561002 and 30561003 respectively.
■Standard window size supported by the packet network: both receiving 
window and sending window are 5.
■Standard maximum packet length: both maximum receiving packet length and 
maximum sending packet length are 512.
■Channel range: permanent virtual circuit section, incoming-only channel 
section and outgoing-only channel section are disabled, two-way channel 
section is [1, 31].  
						

							226CHAPTER 16: CONFIGURING LAPB AND X.25
II. Networking Diagram
Figure 69   Connect the router to X.25 public packet network
III. Configuration Procedure
1Configure Router A:
aConfigure interface IP address
[Router]interface Serial 0
[Router-Serial0]ip address 168.173.24.1 255.255.255.0
bConnect to public packet network, make the router as DTE side
[Router-Serial0]link-protocol x25 dte
[Router-Serial0]x25 x121-address 30561001
[Router-Serial0]x25 window-size 5 5
[Router-Serial0]x25 packet-size 512 512
[Router-Serial0]x25 map ip 168.173.24.2 x121-address 30561002
[Router-Serial0]x25 map ip 168.173.24.3 x121-address 30561003
2Configure Router B:
aConfigure interface IP address
[Router]configure
[Router]interface Serial 0
[Router-Serial0]ip address 168.173.24.2 255.255.255.0
bConnect to public packet network, make the router as DTE side
[Router-Serial0]link-protocol x25 dte
[Router-Serial0]x25 x121-address 30561002
[Router-Serial0]x25 window-size 5 5
[Router-Serial0]x25 packet-size 512 512
[Router-Serial0]x25 map ip 168.173.24.1 x121-address 30561001
[Router-Serial0]x25 map ip 168.173.24.3 x121-address 30561003
3Configure Router C:
aConfigure interface IP address
[Router]interface Serial 0
[Router-Serial0]ip address 168.173.24.3 255.255.255.0
bConnect to public packet network, make the router as DTE side
[Router-Serial0]link-protocol x25 dte
[Router-Serial0]x25 x121-address 30561003
[Router-Serial0]x25 window-size 5 5
[Router-Serial0]x25 packet-size 512 512
RouterARouterB
RouterC Serial0
Serial0 Serial0
IP: 168.173.24.1
X.121: 30561001IP: 168.173.24.2
X.121: 30561002
X.25
windowsize: 5 5
packetsize: 512 512