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Page 96 / 252 Scroll up to view Page 91 - 95
Chapter 13 DHCP Server
NBG5715 User’s Guide
96
The following table describes the labels in this screen.
13.3
The DHCP Server Advanced Screen
This screen allows you to assign IP addresses on the LAN to specific individual computers based on
their MAC addresses. You can also use this screen to configure the DNS server information that the
NBG5715 sends to the DHCP clients.
To change your NBG5715’s static DHCP settings, click
Network
>
DHCP Server
>
Advanced
. The
following screen displays.
Figure 59
Network > DHCP Server > Advanced
Table 41
Network > DHCP Server > General
LABEL
DESCRIPTION
DHCP Server
Select
Enable
to activate DHCP for LAN.
DHCP (Dynamic Host Configuration Protocol, RFC 2131 and RFC 2132)
allows individual clients (computers) to obtain TCP/IP configuration at
startup from a server. Enable the DHCP server unless your ISP instructs you
to do otherwise. Select
Disable
to stop the NBG5715 acting as a DHCP
server. When configured as a server, the NBG5715 provides TCP/IP
configuration for the clients. If not, DHCP service is disabled and you must
have another DHCP server on your LAN, or else the computers must be
manually configured. When set as a server, fill in the following four fields.
IP Pool Starting
Address
This field specifies the first of the contiguous addresses in the IP address
pool for LAN.
Pool Size
This field specifies the size, or count of the IP address pool for LAN.
Apply
Click
Apply
to save your changes back to the NBG5715.
Cancel
Click
Cancel
to begin configuring this screen afresh.
Page 97 / 252
Chapter 13 DHCP Server
NBG5715 User’s Guide
97
The following table describes the labels in this screen.
13.4
The Client List Screen
The DHCP table shows current DHCP client information (including IP Address, Host Name and MAC
Address) of network clients using the NBG5715’s DHCP servers.
Configure this screen to always assign an IP address to a MAC address (and host name). Click
Network > DHCP Server > Client List
.
Note: You can also view a read-only client list by clicking the
DHCP Table (Details...)
hyperlink in the
Status
screen.
Table 42
Network > DHCP Server > Advanced
LABEL
DESCRIPTION
Static DHCP Table
#
This is the index number of the static IP table entry (row).
MAC Address
Type the MAC address (with colons) of a computer on your LAN.
IP Address
Type the LAN IP address of a computer on your LAN.
DNS Server
DNS Servers
Assigned by DHCP
Server
The NBG5715 passes a DNS (Domain Name System) server IP address (in the
order you specify here) to the DHCP clients. The NBG5715 only passes this
information to the LAN DHCP clients when you select the
Enable DHCP Server
check box. When you clear the
Enable DHCP Server
check box, DHCP service
is disabled and you must have another DHCP sever on your LAN, or else the
computers must have their DNS server addresses manually configured.
First DNS Server
Second DNS Server
Third DNS Server
Select
From ISP
if your ISP dynamically assigns DNS server information (and
the NBG5715's WAN IP address). The field to the right displays the (read-only)
DNS server IP address that the ISP assigns.
Select
User-Defined
if you have the IP address of a DNS server. Enter the
DNS server's IP address in the field to the right. If you chose
User-Defined
,
but leave the IP address set to 0.0.0.0,
User-Defined
changes to
None
after
you click
Apply
. If you set a second choice to
User-Defined
, and enter the
same IP address, the second
User-Defined
changes to
None
after you click
Apply
.
Select
DNS Relay
to have the NBG5715 act as a DNS proxy. The NBG5715's
LAN IP address displays in the field to the right (read-only). The NBG5715 tells
the DHCP clients on the LAN that the NBG5715 itself is the DNS server. When a
computer on the LAN sends a DNS query to the NBG5715, the NBG5715
forwards the query to the NBG5715's system DNS server (configured in the
WAN > Internet Connection
screen) and relays the response back to the
computer. You can only select
DNS Relay
for one of the three servers; if you
select
DNS Relay
for a second or third DNS server, that choice changes to
None
after you click
Apply
.
Select
None
if you do not want to configure DNS servers. If you do not
configure a DNS server, you must know the IP address of a computer in order
to access it.
Apply
Click
Apply
to save your changes back to the NBG5715.
Cancel
Click
Cancel
to begin configuring this screen afresh.
Page 98 / 252
Chapter 13 DHCP Server
NBG5715 User’s Guide
98
Figure 60
Network > DHCP Server > Client List
The following table describes the labels in this screen.
Table 43
Network > DHCP Server > Client List
LABEL
DESCRIPTION
#
This is the index number of the host computer.
Status
This field displays whether the connection to the host computer is up (a yellow bulb)
or down (a gray bulb).
Host Name
This field displays the computer host name.
IP Address
This field displays the IP address relative to the # field listed above.
MAC Address
This field shows the MAC address of the computer with the name in the
Host Name
field.
Every Ethernet device has a unique MAC (Media Access Control) address which
uniquely identifies a device. The MAC address is assigned at the factory and consists
of six pairs of hexadecimal characters, for example, 00:A0:C5:00:00:02.
Reserve
Select this if you want to reserve the IP address for this specific MAC address.
Apply
Click
Apply
to save your changes back to the NBG5715.
Reset
Click
Cancel
to reload the previous configuration for this screen.
Page 99 / 252
NBG5715 User’s Guide
99
C
HAPTER
14
NAT
14.1
Overview
NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a host in
a packet. For example, the source address of an outgoing packet, used within one network is
changed to a different IP address known within another network.
The figure below is a simple illustration of a NAT network. You want to assign ports 21-25 to one
FTP, Telnet and SMTP server (
A
in the example), port 80 to another (
B
in the example) and assign
a default server IP address of 192.168.1.35 to a third (
C
in the example).
You assign the LAN IP addresses to the devices (
A
to
D
) connected to your NBG5715. The ISP
assigns the WAN IP address. The NAT network appears as a single host on the Internet. All traffic
coming from
A
to
D
going out to the Internet use the IP address of the NBG5715, which is
192.168.1.1.
Figure 61
NAT Example
This chapter discusses how to configure NAT on the NBG5715.
Note: You must create a firewall rule in addition to setting up NAT, to allow traffic from
the WAN to be forwarded through the NBG5715.
14.1.1
What You Can Do in this Chapter
•
Use the
General
screen to enable NAT and set a default server (
Section 14.2 on page 101
).
•
Use the
Port Forwarding
screen to forward incoming service requests to the server(s) on your
local network (
Section 14.3 on page 102
).
A: 192.168.1.33
B: 192.168.1.34
C: 192.168.1.35
IP address
192.168.1.1
WAN
LAN
assigned by ISP
FTP, Telnet, SNMP
Port 80
Ports 21 to 25
Page 100 / 252
Chapter 14 NAT
NBG5715 User’s Guide
100
•
Use the
NAT Advance
screen to change your NBG5715’s trigger port settings (
Section 14.4 on
page 105
).
14.1.2
What You Need To Know
The following terms and concepts may help as you read through this chapter.
Inside/Outside
This denotes where a host is located relative to the NBG5715, for example, the computers of your
subscribers are the inside hosts, while the web servers on the Internet are the outside hosts.
Global/Local
This denotes the IP address of a host in a packet as the packet traverses a router, for example, the
local address refers to the IP address of a host when the packet is in the local network, while the
global address refers to the IP address of the host when the same packet is traveling in the WAN
side.
Note: Inside/outside refers to the location of a host, while global/local refers to the IP
address of a host used in a packet.
An inside local address (ILA) is the IP address of an inside host in a packet when the packet is still
in the local network, while an inside global address (IGA) is the IP address of the same inside host
when the packet is on the WAN side. The following table summarizes this information.
Note: NAT never changes the IP address (either local or global) of an outside host.
What NAT Does
In the simplest form, NAT changes the source IP address in a packet received from a subscriber
(the inside local address) to another (the inside global address) before forwarding the packet to the
WAN side. When the response comes back, NAT translates the destination address (the inside
global address) back to the inside local address before forwarding it to the original inside host. Note
that the IP address (either local or global) of an outside host is never changed.
The global IP addresses for the inside hosts can be either static or dynamically assigned by the ISP.
In addition, you can designate servers, for example, a web server and a telnet server, on your local
network and make them accessible to the outside world. If you do not define any servers , NAT
offers the additional benefit of firewall protection. With no servers defined, your NBG5715 filters out
Table 44
NAT Definitions
ITEM
DESCRIPTION
Inside
This refers to the host on the LAN.
Outside
This refers to the host on the WAN.
Local
This refers to the packet address (source or
destination) as the packet travels on the LAN.
Global
This refers to the packet address (source or
destination) as the packet travels on the WAN.

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