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Page 156 / 412 Scroll up to view Page 151 - 155
Chapter 9 Quality of Service (QoS)
VMG8924-B10A and VMG8924-B30A Series User’s Guide
156
All packets are evaluated against the PIR. If a packet exceeds the PIR it is marked red. Otherwise it
is evaluated against the CIR. If it exceeds the CIR then it is marked yellow. Finally, if it is below the
CIR then it is marked green.
The following shows how tokens work with incoming packets in trTCM:
•
A packet arrives. If the number of tokens in the PBS bucket is less than the size of the packet (in
bytes), the packet is marked red and may be dropped regardless of the CBS bucket. No tokens
are removed if the packet is dropped.
•
If the PBS bucket has enough tokens, the Device checks the CBS bucket. The packet is marked
green and can be transmitted if the number of tokens in the CBS bucket is equal to or greater
than the size of the packet (in bytes). Otherwise, the packet is marked yellow.
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157
C
HAPTER
10
Network Address Translation (NAT)
10.1
Overview
This chapter discusses how to configure NAT on the Device. 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 to a different IP address known within
another network.
10.1.1
What You Can Do in this Chapter
•
Use the
Port Forwarding
screen to configure forward incoming service requests to the server(s)
on your local network (
Section 10.2 on page 158
).
•
Use the
Applications
screen to forward incoming service requests to the server(s) on your local
network (
Section 10.3 on page 161
).
•
Use the
Port Triggering
screen to add and configure the Device’s trigger port settings (
Section
10.4 on page 163
).
•
Use the
DMZ
screen to configure a default server (
Section 10.5 on page 166
).
•
Use the
ALG
screen to enable and disable the NAT and SIP (VoIP) ALG in the Device (
Section
10.6 on page 166
).
•
Use the
Address Mapping
screen to configure the Device's address mapping settings (
Section
10.7 on page 167
).
•
Use the
Sessions
screen to configure the Device's maximum number of NAT sessions (
Section
10.7 on page 167
).
10.1.2
What You Need To Know
Inside/Outside
Inside/outside denotes where a host is located relative to the Device, for example, the computers
of your subscribers are the inside hosts, while the web servers on the Internet are the outside
hosts.
Global/Local
Global/local 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.
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NAT
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.
Port Forwarding
A port forwarding set is a list of inside (behind NAT on the LAN) servers, for example, web or FTP,
that you can make visible to the outside world even though NAT makes your whole inside network
appear as a single computer to the outside world.
Finding Out More
See
Section 10.10 on page 170
for advanced technical information on NAT.
10.2
The Port Forwarding Screen
Use the
Port Forwarding
screen to forward incoming service requests to the server(s) on your
local network.
You may enter a single port number or a range of port numbers to be forwarded, and the local IP
address of the desired server. The port number identifies a service; for example, web service is on
port 80 and FTP on port 21. In some cases, such as for unknown services or where one server can
support more than one service (for example both FTP and web service), it might be better to
specify a range of port numbers. You can allocate a server IP address that corresponds to a port or
a range of ports.
The most often used port numbers and services are shown in
Appendix G on page 397
. Please refer
to RFC 1700 for further information about port numbers.
Note: Many residential broadband ISP accounts do not allow you to run any server
processes (such as a Web or FTP server) from your location. Your ISP may
periodically check for servers and may suspend your account if it discovers any
active services at your location. If you are unsure, refer to your ISP.
Configuring Servers Behind Port Forwarding (Example)
Let's say 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
Page 159 / 412
Chapter 10 Network Address Translation (NAT)
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159
third (
C
in the example). You assign the LAN IP addresses and the ISP assigns the WAN IP address.
The NAT network appears as a single host on the Internet.
Figure 81
Multiple Servers Behind NAT Example
Click
Network Setting > NAT > Port Forwarding
to open the following screen.
See
Appendix G on page 397
for port numbers commonly used for particular services.
Figure 82
Network Setting > NAT > Port Forwarding
The following table describes the fields in this screen.
Table 56
Network Setting > NAT > Port Forwarding
LABEL
DESCRIPTION
Add
Click this to add a new rule.
#
This is the index number of the entry.
Status
This field displays whether the NAT rule is active or not. A yellow bulb signifies that this rule
is active. A gray bulb signifies that this rule is not active. Click the bulb to enable/disable
this rule.
Service Name
This shows the service’s name.
WAN Interface
This shows the WAN interface through which the service is forwarded.
WAN IP
This field displays the incoming packet’s destination IP address.
Server IP
Address
This is the server’s IP address to which the service is forwarded.
Start Port
This is the first external port number that identifies a service.
End Port
This is the last external port number that identifies a service.
Translation
Start Port
This is the first internal port number that identifies a service.
A=192.168.1.33
D=192.168.1.36
C=192.168.1.3
B=192.168.1.34
WAN
LAN
192.168.1.1
IP Address assigned by ISP
Page 160 / 412
Chapter 10 Network Address Translation (NAT)
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160
10.2.1
Add/Edit Port Forwarding
Click
Add new rule
in the
Port Forwarding
screen or click the
Edit
icon next to an existing rule to
open the following screen.
Figure 83
Port Forwarding: Add/Edit
The following table describes the labels in this screen.
Translation End
Port
This is the last internal port number that identifies a service.
Protocol
This shows the IP protocol supported by this virtual server, whether it is
TCP
,
UDP
, or
TCP/
UDP
.
Modify
Click the
Edit
icon to edit this rule.
Click the
Delete
icon to delete an existing rule.
Table 56
Network Setting > NAT > Port Forwarding (continued)
LABEL
DESCRIPTION
Table 57
Port Forwarding: Add/Edit
LABEL
DESCRIPTION
Active
Clear the checkbox to disable the rule. Select the check box to enable it.
Service Name
Enter a name to identify this rule using keyboard characters (A-Z, a-z, 1-2 and so on).
WAN Interface
Select the WAN interface through which the service is forwarded.
You must have already configured a WAN connection with NAT enabled.
WAN IP
Enter the WAN IP address for which the incoming service is destined. If the packet’s
destination IP address doesn’t match the one specified here, the port forwarding rule will
not be applied.

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