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Page 186 / 404 Scroll up to view Page 181 - 185
Chapter 10 Quality of Service (QoS)
P-661HNU-Fx User’s Guide
186
10.5
The QoS Monitor Screen
To view the ZyXEL Device’s QoS packet statistics, click
Network Setting > QoS
>
Monitor
. The screen appears as shown.
Figure 75
Network Setting > QoS > Monitor
DHCP
This field is available only when you select
IP
in the
Ether Type
field,
and
UDP
in the
IP Protocol
field.
Select this option and select a DHCP option.
If you select
Vendor Class ID (DHCP Option 60)
, enter the
Class
ID
of the matched traffic, such as the type of the hardware or
firmware.
If you select
ClientID (DHCP Option 61)
, enter the
Type
of the
matched traffic and
Client ID
of the DHCP client.
If you select
User Class ID (DHCP Option 77)
, enter the
User
Class Data
, which is a string that identifies the user’s category or
application type in the matched DHCP packets.
If you select
VendorSpecificIntro (DHCP Option 125)
, enter the
Enterprise Number
of the software of the matched traffic and
Vendor Class Data
used by all the DHCP clients.
Service
Select the service classification of the traffic.
Exclude
Select this option to exclude the packets that match the specified
criteria from this classifier.
Apply
Click
Apply
to save your changes.
Back
Click
Back
to return to the previous screen without saving.
Table 41
Class Setup: Add/Edit (continued)
LABEL
DESCRIPTION
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Chapter 10 Quality of Service (QoS)
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187
The following table describes the labels in this screen.
10.6
QoS Technical Reference
This section provides some technical background information about the topics
covered in this chapter.
10.6.1
IP Precedence
Similar to IEEE 802.1p prioritization at layer-2, you can use IP precedence to
prioritize packets in a layer-3 network. IP precedence uses three bits of the eight-
bit ToS (Type of Service) field in the IP header. There are eight classes of services
(ranging from zero to seven) in IP precedence. Zero is the lowest priority level and
seven is the highest.
10.6.2
DiffServ
QoS is used to prioritize source-to-destination traffic flows. All packets in the flow
are given the same priority. You can use CoS (class of service) to give different
priorities to different packet types.
DiffServ (Differentiated Services) is a class of service (CoS) model that marks
packets so that they receive specific per-hop treatment at DiffServ-compliant
network devices along the route based on the application types and traffic flow.
Table 42
Network Setting > QoS > Monitor
LABEL
DESCRIPTION
Monitor
Refresh Interval
Select how often you want the ZyXEL Device to update this screen.
Select
No Refresh
to stop refreshing statistics.
Status
#
This is the index number of the entry.
Name
This shows the name of the WAN interface on the ZyXEL Device.
Pass Rate (bps)
This shows how many packets forwarded to this interface are
transmitted successfully.
Queue Monitor
#
This is the index number of the entry.
Name
This shows the name of the queue.
Interface
The type of connection that the traffic is going through
Pass Rate (bps)
This shows how many packets assigned to this queue are transmitted
successfully.
Drop Rate (bps)
This shows how many packets assigned to this queue are dropped.
Page 188 / 404
Chapter 10 Quality of Service (QoS)
P-661HNU-Fx User’s Guide
188
Packets are marked with DiffServ Code Points (DSCPs) indicating the level of
service desired. This allows the intermediary DiffServ-compliant network devices
to handle the packets differently depending on the code points without the need to
negotiate paths or remember state information for every flow. In addition,
applications do not have to request a particular service or give advanced notice of
where the traffic is going.
DSCP and Per-Hop Behavior
DiffServ defines a new DS (Differentiated Services) field to replace the Type of
Service (TOS) field in the IP header. The DS field contains a 2-bit unused field and
a 6-bit DSCP field which can define up to 64 service levels. The following figure
illustrates the DS field.
DSCP is backward compatible with the three precedence bits in the ToS octet so
that non-DiffServ compliant, ToS-enabled network device will not conflict with the
DSCP mapping.
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior),
that each packet gets across the DiffServ network. Based on the marking rule,
different kinds of traffic can be marked for different kinds of forwarding. Resources
can then be allocated according to the DSCP values and the configured policies.
DSCP (6 bits)
Unused (2 bits)
Page 189 / 404
P-661HNU-Fx User’s Guide
189
C
HAPTER
11
Network Address Translation
(NAT)
11.1
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 to a different IP address known within another
network.
11.1.1
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 11.2 on page 190
).
•
Use the
Sessions
screen to limit the number of concurrent NAT sessions each
client can use (
Section 11.3 on page 193
).
11.1.2
What You Need To Know
The following terms and concepts may help as you read this chapter.
Inside/Outside and Global/Local
Inside/outside denotes where a host is located relative to the ZyXEL 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 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.
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)
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Chapter 11 Network Address Translation (NAT)
P-661HNU-Fx User’s Guide
190
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 11.4 on page 194
for advanced technical information on NAT.
11.2
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 E on page
359
. 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 third (
C
in the example). You assign the LAN IP

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