3Com Router User Manual

							8
INTERFACE CONFIGURATION 
O
VERVIEW
This chapter contains information on the following topics:
■Interface Configuration Overview
■Configure Interface
■Display and Debug Interface
Interface 
Configuration 
OverviewThe router interface refers to the part through which the router exchanges data 
and interacts with other devices in the network. It functions to implement data 
exchange between the router and other network devices. 
The 3Com Router supports physical interface and logical interface on the router.
Physical interface is an interface physically exists and can be supported by 
corresponding devices, such as the Ethernet interface and 
synchronous/asynchronous serial interface. There are two types of physical 
interfaces. One is the LAN interface, which mainly refers to the Ethernet interface 
through which the router can exchange data with the network devices in LAN. 
Second one is the WAN interface which includes interfaces like the 
synchronous/asynchronous serial interface, asynchronous serial interface, AUX 
interface, CE1/PRI, ISDN BRI interface. Through the WAN interface, the router can 
exchange data with the network devices in the external network. 
Logical interface is an interface that does not physically exist and needs to be 
established through configuration, which can also exchange the data. Logical 
interface includes the Dialer interface, sub-interface, standby center logic channel 
and virtual-template.
Configure Interface
Interface ViewTo facilitate configuration and maintenance of the interface, the interface view has 
to be set in the 3Com Router software. Interface commands will be effective only 
when used in the view of relevant interfaces.
Enter the Interface View 
With interface command in all views, you can enter the specified view of the 
interface.
Ta b l e 80   Enter view of specified interface
OperationCommand
Enter view of specified interfaceinterface type number 
						

							108CHAPTER 8: INTERFACE CONFIGURATION OVERVIEW
In the 3Com Router, the command to enter E1/T1 interface view is controller { 
e1 | t1 }, which is different from the command of other interfaces.
Exit the Interface View.
In the interface view, input quit to return to the system view.
Set Interface DescriptionThe 3Com Router has a configuration item of interface description for router’s 
physical interface. Interface description is mainly used to help identifying the 
usage of interface. Please use this command in interface view.
Ta b l e 81   Set interface description
Set Time Interval for 
Flow Control StatisticsThe 3Com Router system counts interface flow at every time interval and 
calculates the unit flow as the reference for standby center. Other flow control 
methods (including the 
dialer threshold command) need this parameter.
Perform the following configuration in system view.
Ta b l e 82   Set time interval for flow control statistics
The parameter minutes is 5 minutes by default.
Interface Configuration 
MethodBefore configuring an interface, it is necessary to have a clear idea about the 
networking requirement and network diagram. The following operations must be 
implemented at least for the interface configuration.
■If the interface is a physical interface, be clear about the connection state, 
working mode of the physical interface to be selected and related working 
parameters.
■If the interface is a WAN interface, assign the encapsulated link layer protocol 
and working parameters that should be abided by for the opposite port 
connected with this interface.
■Configure network protocol (such as IP) address of this interface.
■Configure the static route that can reach the destination network via this 
interface, or configure working parameters of the dynamic route protocol on 
this interface.
■If the interface supports dial-up, please configure working parameters and 
management to Modem.
■If the interface acts as the main interface or standby interface at the standby 
center application, please configure related working parameters of the standby 
center.
OperationCommand
Set interface descriptiondescription 
interface-description
Recover default interface description.undo description
OperationCommand
Set interval time for flow control on the 
interfaceflow-interval minutes  
						

							Display and Debug Interface109
■If a firewall is to be established on this interface, please configure parameters 
about related message filtering or address conversion.
There are lots of parameters to be configured in the interface view. So, this part 
will mainly introduce configurations of some parameters specific to the physical 
interface, and briefly introduce the logical interface definition. Configurations 
about the link layer protocol, network layer protocol, parameter and some special 
functions (such as dial, standby center, and firewall) will be introduced specifically 
in other parts of this manual and no further details are provided here.
Display and Debug 
InterfacePlease use the following commands in all views.
Ta b l e 83   Display and debug interface
When the physical or protocol state of the interface changes, the system will 
automatically output related prompt information of the interface (e.g., Serial0) as 
shown in following table.
Ta b l e 84   Interface state information
If a physical interface on the router is idle and not connected with cable, use the 
shutdown command to disable the interface in case that the interface goes 
abnormal due to some interference.
OperationCommand
Display current running state and statistic 
information of the interface (in all views)display interfaces [type number 
]
 
display interfaces brief
Clear interface statistic information (in system 
view)reset counters interface [ type 
number ]
Shut down interface (in interface view)shutdown
Restart interface (in interface view)undo shutdown
Interface state informationMeaning
% Interface Serial0 is down The interface is shut down by the user.
% Interface Serial0 is resetThe interface is restarted by the user.
%01:10:34: Interface Serial0 changed state to 
DOWNThe physical state of the interface is 
changed to DOWN
%01:11:03: Interface Serial0 changed state to UPThe physical state of the interface is 
changed to UP
%01:12:02: Line protocol ip on interface Serial0, 
changed state to DOWNThe protocol state of the interface is 
changed to DOWN
%01:11:34: Line protocol ip on interface Serial0, 
changed state to UPThe protocol state of the interface is 
changed to UP 
						

							110CHAPTER 8: INTERFACE CONFIGURATION OVERVIEW 
						

							9
CONFIGURING LAN INTERFACE
This chapter contains information on the following topics:
■Ethernet Interface Overview
■Configure Ethernet Interface
■Display and Debug Ethernet Interface
■Typical Ethernet Interface Configuration Example
■Troubleshooting
Ethernet Interface 
OverviewEthernet interface of the 3Com Router series comprises fast Ethernet interface.
The conventional Ethernet interface complies with 10BASE-T physical layer 
specifications, working at 10 Mbps and in two modes: full duplex and half duplex.
The fast Ethernet interface complies with 100BASE-T and also 10BASE-T physical 
layer specifications, working at 10 Mbps or 100 Mbps, and in two modes: half 
duplex and full duplex. With the auto-negotiation capability, it can consult other 
network devices to determine and automatically select the optimum working 
mode and rate, thus greatly simplifying the configuration and management of the 
system.
Configure Ethernet 
InterfaceEthernet interface configuration includes:
■Enter view of specified Ethernet interface
■Set network protocol address
■Set frame format of sending message
■Set MTU
■Select working rate of fast Ethernet interface
■Select working mode of Ethernet interface
■Enable or disable internal loopback and external loopback.
The specified Ethernet interface cannot be configured unless you enter its view. It 
is necessary to configure IP address. Since there are default values for other 
parameters that can enable the system to work normally in most cases, it is 
recommended not to perform other configuration on Ethernet interface.
1Enter view of specified Ethernet interface
Please use the following command in the all views. 
						

							112CHAPTER 9: CONFIGURING LAN INTERFACE
Ta b l e 85   Enter view of specified Ethernet interface
2Set network protocol address
The 3Com Router supports IP and IPX at Ethernet interface. Therefore, it is 
necessary to configure IP or IPX network address. 
Please use the following commands in Ethernet interface view. 
Ta b l e 86   Set IP address
When an Ethernet interface is configured with two or more IP addresses, use 
keyword sub to identify them.
Please use the ipx enable command in system view, and use the ipx network in 
Ethernet interface view.
Ta b l e 87   Set IPX address
3Set frame format of sending message
Both Ethernet_II and Ethernet_SNAP can support IP and IPX. The Ethernet 
interface can identify these two formats out of received frame, but can only 
choose one frame format for the sent frame.
Please use the following commands in Ethernet interface view.
Ta b l e 88   Set frame format of sending message
The frame format of sending message is Ethernet_II by default.
4Set MTU
Maximum transmission unit (MTU) will influence the fragmentation and 
reassembling of network message. 
Please use the following commands in Ethernet interface view.
Ta b l e 89   Set MTU
OperationCommand
Enter view of specified Ethernet interfaceinterface ethernet number
OperationCommand
Set IP addressip address ip-address ip-mask [ sub ]
Cancel IP addressundo ip address ip-address ip-mask [ 
sub ]
OperationCommand
Specify IPX network node valueipx enable [ node node ]
Delete IPX network node value.undo ipx enable
Specify IPX network numberipx network network-number
Delete IPX network numberundo ipx network
OperationCommand
Set frame format of sending messagesend-frame-type { ethernet_ii | 
ethernet_snap }
Recover default frame format of sending 
messageundo send-frame-type
OperationCommand
Set MTUmtu size 
						

							Display and Debug Ethernet Interface113
Value ranges and default values of MTUs with different link layer protocol are 
different. When Ethernet_II frame format is adopted, MTU value range will be 
46-1500 bytes with the default value as 1500 bytes, and when Ethernet_SNAP 
frame format is adopted, MTU value range will be 46-1492 bytes with default 
value 1492 bytes.
5Select work rate of fast Ethernet interface
As described before, the fast Ethernet interface can work at rates of 10Mbps and 
100Mbps. Therefore, it is possible to select interface working rate with following 
command in Ethernet interface view.
Ta b l e 90   Select working rate of fast Ethernet interface
The default is “negotiation”, i.e. the system automatically chooses an optimum 
working rate. The user can also specify the interface working rate. But the rate 
specified must be the same as that of the actually connected network.
6Select work mode of Ethernet interface
’s Ethernet interface should work in half duplex mode when connected with HUB 
and in full duplex mode when connected with LAN Switch. Therefore, it is possible 
to select working mode with the following command in Ethernet interface view.
Ta b l e 91   Select working mode of Ethernet interface
The default is “negotiation”, i.e. the system automatically chooses an optimum 
working mode.
7Enable or disable internal loopback and external loopback
When performing special functionality test on Ethernet interface, it needs to be 
set as internal loopback and external loopback sometimes. Therefore, it is possible 
to enable internal loopback and external loopback with the following commands 
in Ethernet interface view.
Ta b l e 92   Enable or disable internal loopback and external loopback
The default is to disable both internal loopback and external loopback.
Display and Debug 
Ethernet InterfaceThe following command can be used to view the state of Ethernet interface in all 
views, so that the specified Ethernet interface can be displayed and debugged.
Ta b l e 93   Display the state of specified Ethernet interface
Recover MTU default valueundo mtu
OperationCommand
Select working rate of fast Ethernet interfacespeed { 100 | 10 | negotiation }
OperationCommand
Select working mode of Ethernet interfaceduplex { negotiation | full | 
half }
OperationCommand
Enable internal loopback and external loopbackloopback
Disable internal loopback and external loopbackundo loopback
OperationCommand
Display the state of specified Ethernet 
interfacedisplay interfaces ethernet 
number 
						

							114CHAPTER 9: CONFIGURING LAN INTERFACE
Typical Ethernet 
Interface 
Configuration 
ExampleI. Networking Requirement
As shown below, the Ethernet interfaces of Routers A is connected to IP networks 
192.168.0.0. The computer in LAN connects to the Internet through Router A. Set 
the MTU of Ethernet interface to 1492 bytes, and set the frame format to 
Ethernet_II.
II. Network Diagram
Figure 45   Networking diagram of Ethernet configuration example
III. Configuration Procedure
1Specify the IP address as 192.168.0.1 and the mask as 255.255.255.0.
[Router]interface ethernet 0
[Router-Ethernet0]ip address 192.168.0.1 255.255.255.0
2Set MTU of the interface to 1492 bytes and frame format to Ethernet_II.
[Router-Ethernet0]mtu 1492
[Router-Ethernet0]send-frame-type ethernet_ii
TroubleshootingThe following test methods can be used to check faulty Ethernet interface is 
faulty:
■Ping the Ethernet interface from the host located in the same LAN as the router 
to observe whether the returned messages are correct. 
■View the statistic information of two ends of the connection (such as the router 
and switch) to observe whether the statistic number of the received error 
frames increases quickly.
If either test fails to pass, it indicates that the Ethernet interface of the router or 
the connected Ethernet is abnormal.
After confirming the fault, proceed as follows:
1View whether the LAN connection between the host and router is correct.
If the Ethernet is connected with HUB or LAN Switch, please check the status of 
relevant link indicators on HUB or LAN Switch. If the indicators are on, it means 
that the Ethernet interfaces of the host and router and the network cable are 
physically correct. Otherwise, please replace such faulty physical equipment as the 
network adapter, network cable, router or relevant interface module.
When the Ethernet is connected with unshielded twisted pair and at least one of 
the connected parties supports 100BASE-TX, rate matching must be taken into 
consideration. If the working rates of two parties do not match, i.e. one works in 
100 Mbps mode while the other works in 10 Mbps mode, then the fault is that 
Internet
Interface Address
192.168.0.1
E0LAN
Router A
Network Address
192.168.0.0 
						

							Troubleshooting115
the party with 100 Mbps configuration shows no connection, while the party with 
10 Mbps connection shows the connection has been established. Furthermore, 
the activity indicator of the physical layer blink quickly and messages can not be 
received or transmitted normally.
On checking the connection of fast Ethernet interface of the 3Com Router series, 
the following prompt information is very helpful. Both these two pieces of 
information are output on the control console when the user is executing the rate 
selection command or connecting the network cable.
Ethernet 0: Warning--the link partner do not support 100M mode
Ethernet 0: Warning--the link partner may not support 10M mode
Here, the first piece of prompt information indicates that the opposite end, which 
is detected by the Ethernet interface of the 3Com Router series, does not support 
100 Mbps working rate, while the local end is working at 100 Mbps rate by force. 
At this time, the user should ensure that the opposite side has been configured 
correspondingly and is working at the rate of 100 Mbps. The second prompt 
information indicates that the opposite end, detected by the Ethernet interface of 
the 3Com Router series, may not support 10 Mbps working rate, while the local 
end is forced to work in 10 Mbps rate. Now, the user should ensure the opposite 
end to work at the rate of 10 Mbps. However, when the Ethernet interface of the 
3Com Router series is connecting 10/100 Mbps adaptive port of HUB, this 
information does not mean the setting is incorrect.
2View whether IP addresses of the Ethernet interfaces of the host and router are 
within the same sub-net. That is the network addresses must be the same, only 
the host addresses are different. If they are not in the same sub-net, please re-set 
the IP address.
3Check whether the link layer protocols match one another.
Take for example two link layer protocol standards supporting IP protocol, 
Ethernet_II and Ethernet_SNAP: These two link layer protocols have different 
encapsulation formats and MTU. MTU of the former has 1500 bytes and MTU of 
the latter has 1492 bytes. Two Ethernet devices can not communicate reliably 
unless they are connected with the same link layer protocol. The Ethernet interface 
of the 3Com Router series can simultaneously receive data frames with Ethernet_II 
and Ethernet_SNAP formats. However, the format of sending data frame must be 
in accordance with either Ethernet_II or Ethernet_SNAP as specified by the user. 
Therefore, please confirm whether the data frame sending format of the router is 
the same as that of other hosts. When the protocols do not match although the 
cables and interfaces are physically normal, they can not be pinged through.
4View whether the working mode of the Ethernet interface is correct.
When connecting the Ethernet with unshielded twisted pair or fiber, there are two 
working modes: full duplex and half duplex, specified in 
10BASE-T/100BASE-TX/100BASE-FX standard. When using HUB, the half-duplex 
working mode should be selected. When using LAN Switch, if LAN Switch works 
in half duplex mode, the Ethernet interface of the router also works in half duplex 
mode. If LAN Switch works in full duplex mode, the Ethernet interface of the 
router works in full duplex mode too. If the working mode is incorrect, i.e. one 
party of the connection works in full duplex mode while the other party in half 
duplex mode, fault will occur. That is, when network flow increases, the party 
working in half duplex mode shows frequent network collisions (for example, if  
						

							116CHAPTER 9: CONFIGURING LAN INTERFACE
HUB is connected, all the other devices on the whole network segment will show 
serious network collisions), while the party working in full duplex mode shows 
large amount of error messages received, accompanied with serious message 
losses at both parties. In this case, use 
display interfaces ethernet command 
to view the error ratio of transceiving messages of the Ethernet interface. Usually, 
the collision can be observed through the status indicator of the network 
interface.