Draytek Vigor2136 Series User Manual page 53

II-1-3 LAN
A LAN(Local Area Network) comprises a collection of LAN clients, which are networked devices on
your premises. A LAN client can be a computer, a printer, a Voice-over-IP (VoIP) phone, a mobile
phone, a gaming console, an Internet Protocol Television (IPTV), etc, and can have either a wired
(using Ethernet cabling) or wireless (using Wi-Fi) network connection.
LAN clients within the same LAN are normally able to communicate with one another directly, as
they are peers to one another, unless measures, such as firewalls or VLANs, have been put in place
to restrict such access. Nowadays the most common LAN firewalls are implemented on the LAN
client itself. For example, Microsoft Windows since Windows XP and Apple OS X have built-in
firewalls that can be configured to restrict traffic coming in and going out of the computer. VLANs,
on the other hand, are usually set up using network switches or routers.
To communicate with the hosts outside of the LAN, LAN clients have to go through a network
gateway, which in most cases is a router that sits between the LAN and the ISP network, which is the
WAN. The router acts as a director to ensure traffic between the LAN and the WAN reach their
intended destinations.
IP Address
On most broadband networks, the ISP assigns a single WAN IP address to the subscriber. All LAN
clients have to share this WAN IP address when accessing the Internet. To achieve this, a technique
called Network Address Translation (NAT) is used. Under NAT, a private block of IP addresses is
assigned to the LAN clients, which communicate with WAN hosts through the router, also known as
the gateway.
On outgoing traffic to the WAN, the router makes note that a LAN client has attempted to reach a
WAN host, and forwards the request to the intended WAN recipient.
On traffic incoming to the LAN from a WAN host, the router checks its records to see if a matching
outstanding request from a LAN client to this WAN host exists, and if so, forwards it to the LAN
client. Otherwise, the traffic is dropped.
There are 3 distinct blocks of IPv4 address that are reserved for use as private IP addresses on a
LAN.
Name IP Address Range
24-bit Block 10.0.0.0 to 10.255.255.255
20-bit Block 172.16.0.0 to 172.31.255.255
16-bit Block 192.168.0.0 to 192.168.255.255
The default beginning IP Address of LAN 1 is 192.168.1.1, and the Subnet Mask is 255.255.255.0, for
a total of 254 assignable IP addresses, from 192.168.1.1 to 192.168.1.254. The final IP address of the
selected range is reserved for routing and cannot be assigned to a LAN client.
In most cases, the default IP address block should work satisfactorily. However, there are situations
where you need to select a different address block, such as when you need to communicate with
other LANs that already use the same address block.
Private IP addresses can be assigned automatically to LAN clients using Dynamic Host Configuration
Protocol (DHCP), or manually assigned. The DHCP server can either be the router (the most
common case), or a separate server, that hands out IP addresses to DHCP clients.
Alternatively, static IP addresses can be manually configured on LAN clients as part of their network
settings. No matter how IP addresses are configured, it is important that no two devices get the
same IP address. If both DHCP and static assignment are used on a network, it is important to
exclude the static IP addresses from the DHCP IP pool. For example, if your LAN uses the
192.168.1.x subnet and you have 20 DHCP clients and 20 static IP clients, you could configure
192.168.1.10 as the Start IP Address, 50 as the IP Pool Counts (enough for the current number of
Number of Available Addresses
16,777,216 255.0.0.0
1,048,576 255.240.0.0
65,536
43
Largest Subnet Mask
255.255.0.0