Zyxel NBG4604 Router Manual PDF (Setup & Configuration Guide)

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Chapter 23 Troubleshooting

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201

Make sure that you select the

Enable URL Keyword Blocking

check box in the

Content Filtering screen. Make sure that the keywords that you type are listed in

the

Keyword List

.

If a keyword that is listed in the

Keyword List

is not blocked when it is found in a

URL, customize the keyword blocking using commands. See the Customizing

Keyword Blocking URL Checking section in the Content Filter chapter.

I can access the Internet, but I cannot open my network folders.

In the Network > LAN > Advanced

screen, make sure

Allow between LAN and

WAN

is checked. This is not checked by default to keep the LAN secure.

If you still cannot access a network folder, make sure your account has access

rights to the folder you are trying to open.

I can access the Web Configurator after I switched to AP mode.

When you change from router mode to AP mode, your computer must have an IP

address in the range between “192.168.1.3” and “192.168.1.254”.

Refer to

Appendix C on page 221

for instructions on how to change your

computer’s IP address.

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203

A

PPENDIX

A

IP Addresses and Subnetting

This appendix introduces IP addresses and subnet masks.

IP addresses identify individual devices on a network. Every networking device

(including computers, servers, routers, printers, etc.) needs an IP address to

communicate across the network. These networking devices are also known as

hosts.

Subnet masks determine the maximum number of possible hosts on a network.

You can also use subnet masks to divide one network into multiple sub-networks.

Introduction to IP Addresses

One part of the IP address is the network number, and the other part is the host

ID. In the same way that houses on a street share a common street name, the

hosts on a network share a common network number. Similarly, as each house

has its own house number, each host on the network has its own unique

identifying number - the host ID. Routers use the network number to send packets

to the correct network, while the host ID determines to which host on the network

the packets are delivered.

Structure

An IP address is made up of four parts, written in dotted decimal notation (for

example, 192.168.1.1). Each of these four parts is known as an octet. An octet is

an eight-digit binary number (for example 11000000, which is 192 in decimal

notation).

Therefore, each octet has a possible range of 00000000 to 11111111 in binary, or

0 to 255 in decimal.

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The following figure shows an example IP address in which the first three octets

(192.168.1) are the network number, and the fourth octet (16) is the host ID.

Figure 127

Network Number and Host ID

How much of the IP address is the network number and how much is the host ID

varies according to the subnet mask.

Subnet Masks

A subnet mask is used to determine which bits are part of the network number,

and which bits are part of the host ID (using a logical AND operation). The term

“subnet” is short for “sub-network”.

A subnet mask has 32 bits. If a bit in the subnet mask is a “1” then the

corresponding bit in the IP address is part of the network number. If a bit in the

subnet mask is “0” then the corresponding bit in the IP address is part of the host

ID.

The following example shows a subnet mask identifying the network number (in

bold text) and host ID of an IP address (192.168.1.2 in decimal).

Table 75

Subnet Mask - Identifying Network Number

1ST

OCTET:

(192)

2ND

OCTET:

(168)

3RD

OCTET:

(1)

4TH

OCTET

(2)

IP Address (Binary)

11000000

10101000

00000001

00000010

Subnet Mask (Binary)

11111111

00000000

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Appendix A IP Addresses and Subnetting

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205

By convention, subnet masks always consist of a continuous sequence of ones

beginning from the leftmost bit of the mask, followed by a continuous sequence of

zeros, for a total number of 32 bits.

Subnet masks can be referred to by the size of the network number part (the bits

with a “1” value). For example, an “8-bit mask” means that the first 8 bits of the

mask are ones and the remaining 24 bits are zeroes.

Subnet masks are expressed in dotted decimal notation just like IP addresses. The

following examples show the binary and decimal notation for 8-bit, 16-bit, 24-bit

and 29-bit subnet masks.

Network Size

The size of the network number determines the maximum number of possible

hosts you can have on your network. The larger the number of network number

bits, the smaller the number of remaining host ID bits.

An IP address with host IDs of all zeros is the IP address of the network

(192.168.1.0 with a 24-bit subnet mask, for example). An IP address with host

IDs of all ones is the broadcast address for that network

(192.168.1.255 with a

24-bit subnet mask, for example).

Network Number

11000000

10101000

00000001

Host ID

00000010

Table 76

Subnet Masks

BINARY

DECIMAL

1ST

OCTET

2ND

OCTET

3RD

OCTET

4TH

OCTET

8-bit mask

11111111

00000000

255.0.0.0

16-bit

mask

11111111

00000000

255.255.0.0

24-bit

mask

11111111

00000000

255.255.255.0

29-bit

mask

11111111

11111000

255.255.255.24

8

Table 75

Subnet Mask - Identifying Network Number

1ST

OCTET:

(192)

2ND

OCTET:

(168)

3RD

OCTET:

(1)

4TH

OCTET

(2)

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