3Com Router User Manual

Configure DHCP Relay 347
II. Networking Diagram
Figure 128   Networking diagram of an DHCP relay configuration example 
III. Configuration Procedure
1Configure DHCP relay router:
[Router-Ethernet0] ip address 10.110.1.1 255.255.0.0
[Router-Ethernet0] ip relay-address 202.38.160.2
To configure helper address 202.38.160.2 on the Ethernet interface 0 you need to 
specify the address for the DHCP server. When requesting for configuration 
information, the DHCP client host sends out a DHCP broadcast message....

348CHAPTER 21: CONFIGURING IP APPLICATION
II. Networking Diagram
Figure 129   Configuration example of transparent transmission forwarding protocol
III. Configuration Procedure
1Configure Router A:
[Router] ip relay protocol udp 69
[Router] interface ethernet 0
[Router-Ethernet0] ip address 10.110.1.1 255.255.0.0
[Router-Ethernet0] ip relay-address 202.38.160.2
Troubleshooting DHCP When DHCP relay or transparent transmission function is abnormal, locate the 
fault with 
display command or debugging...

Configure Network Address Translation (NAT)349
■Check whether the transparent transmission router itself is configured with 
services of the protocol transmitted transparently.
Configure Network 
Address Translation 
(NAT)Network Address Translation (NAT), also known as address proxy, implements the 
function for the private network to visit the external network.
Private Network Address and Public Network Address
Private address refers to the address of the internal network or the host computer. 
Public...

350CHAPTER 21: CONFIGURING IP APPLICATION
203.196.3.23:32814. The destination address and port remains unchanged. In the 
proxy server, it maintains one corresponding table of address port. After the 
WWW server of the external network returns a result, the proxy server will 
translate the destination IP address and port in the result data message to 
10.1.1.48:6084. In this way, the internal computer 10.1.1.48 will be able to visit 
the external server.
The role the Network Address Translation (NAT)...

Configure Network Address Translation (NAT)351
■The debugging of the network becomes even more difficult. For instance, 
when one host machine of the internal network attempts to attack other 
networks, it is very difficult to pinpoint which computer is attacking computer, 
since the IP address of the host machine is shielded.
Performance of Network Address Translation (NAT)
When the speed of the broadband of the link is below 1Mbps, the address 
translation has little impact on the performance of the...

352CHAPTER 21: CONFIGURING IP APPLICATION
access control list, then locate the corresponding data pool according to the 
correlation. Thus, the source address is translated into one address in the data 
pool and the address translation process is completed. In the translation 
correlation form, the necessary corresponding information of the translation, 
including access list, data pool information and the HASH table index 
corresponding to the address pool are recorded.
HASH table is correlated to the...

Configure Network Address Translation (NAT)353
corresponding internal server. During the course of address translation, it will look 
up the resource address of the message, to determine if the message is sent from 
the internal server. If yes, the source address is translated to the corresponding 
public network address.
The information the user needs to configure includes: external address, external 
port, external server address and the type of internal server port and protocol.
Please carry out the...

354CHAPTER 21: CONFIGURING IP APPLICATION
Display and Debug NATTa b l e 388   Display and debug NAT
Ty p i c a l  N AT  
Configuration Example An enterprise is connected to WAN by the address translation function of 
an internal server.
I. Networking Requirement
An enterprise is connected to WAN by the address translation function of the 
3Com Router series. It is required that the enterprise can access the Internet via 
serial port 0 of the 3Com Router series, and provide WWW, FTP and SNMP services 
to...

Configure Network Address Translation (NAT)355
II. Networking Diagram
Figure 132   NAT configuration case networking diagram 1
III. Configuration Procedure
aConfigure address pool and access list
[Router] nat address-group 202.38.160.101 202.38.160.105 pool 1
[Router] acl 1
[Router-acl-1]rule permit source 10.110.10.0 0.0.0.255
bAllow address translation of segment at 10.110.10.0/24
[Router-Serial0] nat outbound 1 address-group pool
cSet internal FTP server
[Router-Serial0] nat server global...

356CHAPTER 21: CONFIGURING IP APPLICATION
The internal LAN of an enterprise can dial-up to access Internet by the 
address translation.
I. Networking Requirement
The internal LAN of an enterprise can dial-up to access Internet through serial port 
S0 by the address translation of the 3Com Router series.
II. Networking Diagram
Figure 133   NAT configuration case networking diagram 2
III. Configuration Procedure
1Configure address access control list and dialer-list
[Router] acl 1
[Router-acl-1] rule...