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8.7

Home Networking Technical Reference

This section provides some technical background information about the topics covered in this

chapter.

8.7.1

LANs, WANs and the AMG1302/AMG1202-TSeries

The actual physical connection determines whether the AMG1302/AMG1202-TSeries ports are LAN

or WAN ports. There are two separate IP networks, one inside the LAN network and the other

outside the WAN network as shown next.

Figure 53

LAN and WAN IP Addresses

8.7.2

DHCP Setup

DHCP (Dynamic Host Configuration Protocol, RFC 2131 and RFC 2132) allows individual clients to

obtain TCP/IP configuration at start-up from a server. You can configure the AMG1302/AMG1202-

TSeries as a DHCP server or disable it. When configured as a server, the AMG1302/AMG1202-

TSeries provides the TCP/IP configuration for the clients. If you turn DHCP service off, you must

have another DHCP server on your LAN, or else the computer must be manually configured.

IP Pool Setup

The AMG1302/AMG1202-TSeries is pre-configured with a pool of IP addresses for the DHCP clients

(DHCP Pool). Do not assign static IP addresses from the DHCP pool to your LAN computers.

8.7.3

DNS Server Addresses

DNS (Domain Name System) maps a domain name to its corresponding IP address and vice versa.

The DNS server is extremely important because without it, you must know the IP address of a

computer before you can access it. The DNS server addresses you enter when you set up DHCP are

passed to the client machines along with the assigned IP address and subnet mask.

There are two ways that an ISP disseminates the DNS server addresses.

•

The ISP tells you the DNS server addresses, usually in the form of an information sheet, when

you sign up. If your ISP gives you DNS server addresses, enter them in the

DNS Server

fields in

the

DHCP Setup

screen.

WAN

LAN

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•

Some ISPs choose to disseminate the DNS server addresses using the DNS server extensions of

IPCP (IP Control Protocol) after the connection is up. If your ISP did not give you explicit DNS

servers, chances are the DNS servers are conveyed through IPCP negotiation. The AMG1302/

AMG1202-TSeries supports the IPCP DNS server extensions through the DNS proxy feature.

Please note that DNS proxy works only when the ISP uses the IPCP DNS server extensions. It

does not mean you can leave the DNS servers out of the DHCP setup under all circumstances. If

your ISP gives you explicit DNS servers, make sure that you enter their IP addresses in the

DHCP Setup

screen.

8.7.4

LAN TCP/IP

The AMG1302/AMG1202-TSeries has built-in DHCP server capability that assigns IP addresses and

DNS servers to systems that support DHCP client capability.

IP Address and Subnet Mask

Similar to the way houses on a street share a common street name, so too do computers on a LAN

share one common network number.

Where you obtain your network number depends on your particular situation. If the ISP or your

network administrator assigns you a block of registered IP addresses, follow their instructions in

selecting the IP addresses and the subnet mask.

If the ISP did not explicitly give you an IP network number, then most likely you have a single user

account and the ISP will assign you a dynamic IP address when the connection is established. If this

is the case, it is recommended that you select a network number from 192.168.0.0 to

192.168.255.0 and you must enable the Network Address Translation (NAT) feature of the

AMG1302/AMG1202-TSeries. The Internet Assigned Number Authority (IANA) reserved this block of

addresses specifically for private use; please do not use any other number unless you are told

otherwise. Let's say you select 192.168.1.0 as the network number; which covers 254 individual

addresses, from 192.168.1.1 to 192.168.1.254 (zero and 255 are reserved). In other words, the

first three numbers specify the network number while the last number identifies an individual

computer on that network.

Once you have decided on the network number, pick an IP address that is easy to remember, for

instance, 192.168.1.1, for your AMG1302/AMG1202-TSeries, but make sure that no other device on

your network is using that IP address.

The subnet mask specifies the network number portion of an IP address. Your AMG1302/AMG1202-

TSeries will compute the subnet mask automatically based on the IP address that you entered. You

don't need to change the subnet mask computed by the AMG1302/AMG1202-TSeries unless you

are instructed to do otherwise.

Private IP Addresses

Every machine on the Internet must have a unique address. If your networks are isolated from the

Internet, for example, only between your two branch offices, you can assign any IP addresses to

the hosts without problems. However, the Internet Assigned Numbers Authority (IANA) has

reserved the following three blocks of IP addresses specifically for private networks:

• 10.0.0.0

— 10.255.255.255

• 172.16.0.0

— 172.31.255.255

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•

192.168.0.0 — 192.168.255.255

You can obtain your IP address from the IANA, from an ISP or it can be assigned from a private

network. If you belong to a small organization and your Internet access is through an ISP, the ISP

can provide you with the Internet addresses for your local networks. On the other hand, if you are

part of a much larger organization, you should consult your network administrator for the

appropriate IP addresses.

Note: Regardless of your particular situation, do not create an arbitrary IP address;

always follow the guidelines above. For more information on address assignment,

please refer to RFC 1597, “Address Allocation for Private Internets”

and RFC 1466,

“Guidelines for Management of IP Address Space”.

8.7.5

RIP Setup

RIP (Routing Information Protocol) allows a router to exchange routing information with other

routers. The

RIP Direction

field controls the sending and receiving of RIP packets. When set to:

•

Both -

the AMG1302/AMG1202-TSeries will broadcast its routing table periodically and

incorporate the RIP information that it receives.

•

In Only -

the AMG1302/AMG1202-TSeries will not send any RIP packets but will accept all RIP

packets received.

•

Out Only -

the AMG1302/AMG1202-TSeries will send out RIP packets but will not accept any RIP

packets received.

•

None -

the AMG1302/AMG1202-TSeries will not send any RIP packets and will ignore any RIP

packets received.

The

Version

field controls the format and the broadcasting method of the RIP packets that the

AMG1302/AMG1202-TSeries sends (it recognizes both formats when receiving). RIP-1 is universally

supported; but RIP-2 carries more information. RIP-1 is probably adequate for most networks,

unless you have an unusual network topology.

Both RIP-2B and RIP-2M sends the routing data in RIP-2 format; the difference being that RIP-2B

uses subnet broadcasting while RIP-2M uses multicasting.

Multicasting can reduce the load on

non-router machines since they generally do not listen to the RIP multicast address and so will not

receive the RIP packets. However, if one router uses multicasting, then all routers on your network

must use multicasting, also.

8.7.6

Multicast

Traditionally, IP packets are transmitted in one of either two ways - Unicast (1 sender - 1 recipient)

or Broadcast (1 sender - everybody on the network). Multicast delivers IP packets to a group of

hosts on the network - not everybody and not just 1.

IGMP (Internet Group Multicast Protocol) is a network-layer protocol used to establish membership

in a Multicast group - it is not used to carry user data. IGMP version 2 (RFC 2236) is an

improvement over version 1 (RFC 1112) but IGMP version 1 is still in wide use. IGMP version 3

supports source filtering, reporting or ignoring traffic from specific source address to a particular

host on the network. If you would like to read more detailed information about interoperability

between IGMP version 2 and version 1, please see sections 4 and 5 of RFC 2236. The class D IP

address is used to identify host groups and can be in the range 224.0.0.0 to 239.255.255.255. The

address 224.0.0.0 is not assigned to any group and is used by IP multicast computers. The address

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224.0.0.1 is used for query messages and is assigned to the permanent group of all IP hosts

(including gateways). All hosts must join the 224.0.0.1 group in order to participate in IGMP. The

address 224.0.0.2 is assigned to the multicast routers group.

At start up, the AMG1302/AMG1202-TSeries queries all directly connected networks to gather

group membership. After that, the AMG1302/AMG1202-TSeries periodically updates this

information. IP multicasting can be enabled/disabled on the AMG1302/AMG1202-TSeries LAN and/

or WAN interfaces in the web configurator (

LAN

;

WAN

). Select

None

to disable IP multicasting on

these interfaces.

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C

HAPTER

9

Static Route

9.1

Overview

The AMG1302/AMG1202-TSeries usually uses the default gateway to route outbound traffic from

computers on the LAN to the Internet. To have the AMG1302/AMG1202-TSeries send data to

devices not reachable through the default gateway, use static routes.

For example, the next figure shows a computer (

A

) connected to the AMG1302/AMG1202-TSeries’s

LAN interface. The AMG1302/AMG1202-TSeries routes most traffic from

A

to the Internet through

the AMG1302/AMG1202-TSeries’s default gateway (

R1

). You create one static route to connect to

services offered by your ISP behind router

R2

. You create another static route to communicate with

a separate network behind a router

R3

connected to the LAN.

Figure 54

Example of Static Routing Topology

WAN

R1

R2

A

R3

LAN