Zyxel VMG8924-B30A Router Manual PDF (Setup & Configuration Guide)

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Appendix B Setting up Your Computer’s IP Address

VMG8924-B10A and VMG8924-B30A Series User’s Guide

356

2

If you know your DNS server IP address(es), enter the DNS server information in the

resolv.conf

file in the

/etc

directory.

The following figure shows an example where two DNS server IP

addresses are specified.

Figure 223

Red Hat 9.0: DNS Settings in resolv.conf

3

After you edit and save the configuration files, you must restart the network card. Enter

./network

restart

in the

/etc/rc.d/init.d

directory.

The following figure shows an example.

Figure 224

Red Hat 9.0: Restart Ethernet Card

Verifying Settings

Enter

ifconfig

in a terminal screen to check your TCP/IP properties.

Figure 225

Red Hat 9.0: Checking TCP/IP Properties

nameserver 172.23.5.1

nameserver 172.23.5.2

[root@localhost init.d]# network restart

Shutting down interface eth0:

[OK]

Shutting down loopback interface:

[OK]

Setting network parameters:

[OK]

Bringing up loopback interface:

[OK]

Bringing up interface eth0:

[OK]

[root@localhost]# ifconfig

eth0

Link encap:Ethernet

HWaddr 00:50:BA:72:5B:44

inet addr:172.23.19.129

Bcast:172.23.19.255

Mask:255.255.255.0

UP BROADCAST RUNNING MULTICAST

MTU:1500

Metric:1

RX packets:717 errors:0 dropped:0 overruns:0 frame:0

TX packets:13 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:100

RX bytes:730412 (713.2 Kb)

TX bytes:1570 (1.5 Kb)

Interrupt:10 Base address:0x1000

[root@localhost]#

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357

A

PPENDIX

C

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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Appendix C IP Addresses and Subnetting

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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 226

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).

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.

Table 153

Subnet Masks

1ST OCTET:

(192)

2ND

OCTET:

(168)

3RD

OCTET:

(1)

4TH OCTET

(2)

IP Address (Binary)

11000000

10101000

00000001

00000010

Subnet Mask (Binary)

11111111

00000000

Network Number

11000000

10101000

00000001

Host ID

00000010

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Appendix C IP Addresses and Subnetting

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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).

As these two IP addresses cannot be used for individual hosts, calculate the maximum number of

possible hosts in a network as follows:

Notation

Since the mask is always a continuous number of ones beginning from the left, followed by a

continuous number of zeros for the remainder of the 32 bit mask, you can simply specify the

number of ones instead of writing the value of each octet. This is usually specified by writing a “/”

followed by the number of bits in the mask after the address.

For example, 192.1.1.0 /25 is equivalent to saying 192.1.1.0 with subnet mask 255.255.255.128.

Table 154

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

255.255.255.248

Table 155

Maximum Host Numbers

SUBNET MASK

HOST ID SIZE

MAXIMUM NUMBER OF HOSTS

8 bits

255.0.0.0

24 bits

2

24

– 2

16777214

16 bits

255.255.0.0

16 bits

2

16

– 2

65534

24 bits

255.255.255.0

8 bits

2

8

– 2

254

29 bits

255.255.255.24

8

3 bits

2

3

– 2

6

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Appendix C IP Addresses and Subnetting

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The following table shows some possible subnet masks using both notations.

Subnetting

You can use subnetting to divide one network into multiple sub-networks. In the following example

a network administrator creates two sub-networks to isolate a group of servers from the rest of the

company network for security reasons.

In this example, the company network address is 192.168.1.0. The first three octets of the address

(192.168.1) are the network number, and the remaining octet is the host ID, allowing a maximum

of 2

8

– 2 or 254 possible hosts.

The following figure shows the company network before subnetting.

Figure 227

Subnetting Example: Before Subnetting

You can “borrow” one of the host ID bits to divide the network 192.168.1.0 into two separate sub-

networks. The subnet mask is now 25 bits (255.255.255.128 or /25).

The “borrowed” host ID bit can have a value of either 0 or 1, allowing two subnets; 192.168.1.0 /25

and 192.168.1.128 /25.

Table 156

Alternative Subnet Mask Notation

SUBNET MASK

ALTERNATIVE

NOTATION

LAST OCTET

(BINARY)

LAST OCTET

(DECIMAL)

255.255.255.0

/24

0000 0000

0

255.255.255.128

/25

1000 0000

128

255.255.255.192

/26

1100 0000

192

255.255.255.224

/27

1110 0000

224

255.255.255.240

/28

1111 0000

240

255.255.255.248

/29

1111 1000

248

255.255.255.252

/30

1111 1100

252

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