D-Link D Link 500 B Manual

							DSL-500 ADSL Router User’s Guide
46
Connection Type
Connection Type Window (PPPoE)
The default connection method used by the Router for the WAN connection is
PPP over Ethernet. If you wish to use this method you do not need to change this
setting. However if you are using a static IP address (also called “Bridged
Ethernet” encapsulation as defined by RFC 1483), or PPP over ATM (RFC 2364)
you can select them here.
To change the connection method, select either Router with RFC 1483
 or
Router with PPPoA
 from the pull down menu in the Encapsulation Protocol
field and click OK. If you are changing the connection type to Router with RFC
1483, read the next section. If you are changing it to Router with PPPoA, read
the PPPoA Configuration section. 
						

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Static IP Address Configuration (for RFC 1483)
Static IP Address Configuration Window
In the Static IP Address configuration window enter the static IP Address
 and
subnet mask assigned by your network service provider for your WAN interface.
The Static IP Address is a globally unique IP address used to identify the Router
on the Internet. If you are given a Default Gateway
 IP address enter that here
as well. The default gateway is another Router used to provide Internet access for
many network clients.
You must enter the VPI
 and VCI
 values for the ADSL service here. Check the
values for all of the entries in this window to be certain that they are correct and
click the OK
 button. 
						

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PPPoA Configuration
PPPoA Configuration
PVC
Use this field to assign the VPI
 and VCI
 values for the Router. These numbers
are given to you by your DSL service provider and must be entered in order to
establish the ADSL connection.
PPPoA Login
Use this field to assign a Login User Name
 and Password
 used for
authentication by your network service provider. Type in the user name and
password in their respective fields. You can use any combination of up to 64
characters (no spaces) in both fields.
The Authentication 
protocol used to confirm the identity of the user can be
chosen from the pull-down menu. The available protocols are chap 
(by default)
and pap
.
The Connect on Demand 
pull-down menu toggles either enabled
 or disabled
.
When this function is enabled the router will connect any workstation on your
LAN to the Internet upon request. If this function is disabled, it will be necessary
to access this menu and hit the Connect button each time you want to establish a
connection to the WAN or the Internet. Most users will probably want to enable
this feature. 
						

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If your network account is not billed according to the amount of time connected,
the Idle Time 
field should be left at the default value 0. This means that the
Router is always connected and able to connect on demand.
If your network account is billed according to the amount of time the Router is
actually connected to the Internet, enter an appropriate Idle Time 
value (in
seconds). This will disconnect the Router after the WAN connection has been idle
for the amount of time specified.
PPP Information
This field provides information regarding the status of the Router’s connection to
the WAN. The global IP Address
 for the Router should be assigned
automatically by the network service provider’s PPP server. The Connection
Status
 will read Disconnect until the Router has established the WAN
connection.
Connect to WAN
If you have enabled the Connect on Demand feature, the Router will have
established the WAN connection upon restarting.
If the Connect on Demand feature has been disabled, click the Connect
 button to
initiate the PPP connection via the ADSL WAN interface. The “handshake”
process will take a few seconds.
In the PPPoE or PPPoA Configuration widow, viewing the Connection Status
Connected
, under PPPoA Information
 will indicate a valid connection. A valid
ADSL connection can also be confirmed by observing the LED indicators on the
front panel of the device. 
						

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Line Condition
Line Condition
In the Line Condition window you can monitor the characteristics of the ADSL
connection and confirm that it has been established. From here you can observe
various performance statistics of each end of the connection, including:
Data Path
: Displays the current data path type, Fast
 or Interleaved
.
Operation Mode
: Describes the of modulation technique used to make the
ADSL connection. This will be either Discrete Multi-tone modulation (DMT)
defined by the G.dmt
 standard or the variation of DMT described by the G.lite
standard.
Downstream Rate
: Lists the downstream data transfer rate in Kbps.
Upstream Rate
: Lists the upstream data transfer rate in Kbps.
Near End
 (ADSL Router connection a.k.a. ATU-R): Lists the number of data
transfer errors on the Router end of the ADSL connection. These errors are listed
according to the technique used to correct them. The techniques used are
Forward Error Correction (FEC)
, Cyclic Redundancy Control (CRC)
 and
Header Error Check (HEC)
.
Far End
 (DSLAM): Lists the number of data transfer errors on the DSLAM end
of the ADSL connection. These errors are listed according to the technique used
to correct them. The techniques used are Forward Error Correction (FEC)
,
Cyclic Redundancy Check (CRC)
 and Header Error Control (HEC)
. 
						

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Router Functions
The DHCP and NAT functions of the Router allows the network manager to more
easily manage IP addresses and subnets, and enhance network security by
presenting only one global IP address to the Internet. This section discusses how
to use these conventional routing functions.
DHCP
The Dynamic Host Configuration Protocol (DHCP) allows the Router to assign IP
addresses to all properly configured hosts on the network. Dynamic IP
assignment alleviates the need for the network administrator to maintain and
monitor IP address assignments and simplifies IP use because IP address are
automatically assigned when a station powers-on. Click on the DHCP
Configuration button to see the DHCP menu.
IMPORTANT: If you use DHCP to set your local IP addresses, the IP settings of all
stations on the network must be either manually configured to 0.0.0.0 or, select the
“Obtain an IP address automatically” option under the TCP/IP Properties tab in the
Network menu. See the Configure the Manager PC section at the beginning of Chapter
4 for more explicit instructions.
DHCP Configuration Window
In the DHCP Configuration window you define the following:
Start IP Address
This is the base (starting) address for the IP pool of unassigned IP addresses.
End IP Address
This is the last address of the contiguous IP address range to be used by the
Router for DHCP function. 
						

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Netmask
This mask informs the client, how the destination IP address is to be divided into
network, subnet, and host parts. The netmask has ones in the bit positions in the
32-bit address which are to be used for the network and subnet parts, and zeros
for the host part.
Default Gateway
This specifies the Gateway IP Address that will be assigned to and used by the
DHCP clients.
Leased Time
This specifies the amount of time (in seconds) a client can lease an IP address,
from the dynamically allocated IP pool. A value of 4294967295 means the lease is
permanent.
DNS Server IP
Domain Name Service (DNS) servers are used on the Internet to match the
Uniform Resource Locator (URL) for a website to its Internet IP address.  For
example, the URL: www.cnn.com, is a pseudonym for the IP address:
207.25.71.25.  DNS entries allow users to access resources using URLs instead of
IP addresses.
You may enter any Internet DNS server IP address available through the WAN
connection.  This address should be provided by your network service provider.
(Note that without a DNS server IP, internet sites will only be available using IP
addresses and will not be available using URLs.)
State
This toggles Disable
 and Enable
 for DHCP function.
NAT Configuration
Network Address Translation (NAT) is a routing protocol that allows your
network to become a private
 network that is isolated from, yet connected to the
Internet. It does this by changing the IP address of packets from a global 
IP
address usable on the Internet to a local 
IP address usable on your private
network (but not on the Internet) and vice-versa. The Router allows up to 128
host IP addresses.
NAT has two major benefits. First, NAT allows many users to access the Internet
using a single global IP address. This can greatly reduce the costs associated with
Internet access and also helps alleviate the current shortage of Internet IP
addresses. Secondly, the NAT process creates an added degree of security by
hiding your private network behind one IP address. The NAT function will
normally only allow incoming packets that are generated in response to a request
from a host within the LAN.
If your network uses web servers, FTP servers or other proxies used for data
requests from outside the private network, you can use NAT in conjunction with 
						

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Port Redirection to allow appropriate use of your servers by outside users. See
the section on Port Redirection for more information.
For the purposes of network administration, NAT is almost indispensable. Hosts
and servers on the internal network can be moved easily. Using NAT together
with DHCP can greatly reduce the workload of a network manager while
allowing tremendous flexibility.
NAT Configuration Window
The NAT function is enabled by default on the Router. If you want to disable
NAT, open the NAT Configuration window, select disabled 
in the NAT Function
pull-down menu. Click the OK 
button to implement your choice. There are
security risks associated with disabling NAT, so it is important that you have
other network protection mechanisms in place before you do this. 
						

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Security Features
Network security is an unfortunate necessity for any network connected to the
Internet. Protection of sensitive information and proprietary assets on your
private network should be designed into the network infrastructure from the
beginning. If you are not already, it is recommended that you become familiar
with network security issues and the strategies available to help reduce risks
from outside as well as from within your LAN. The Router provides features that
can enhance your network security and should be used in concert with other
security provisions, such as virus scanning software for all workstations, the use
of proxy servers and stateful inspection methods.
Advanced Filtering and Firewall
One of the most important elements of any network security implementation is
the firewall. Packet filtering is a basic firewall security measure that should be
used on any network that is exposed to security risk. A packet filter system
examines data packets and scrutinizes them for the purpose of controlling
network access. Filtering rules determine whether or not to allow access through
the Router from either side of the gateway. The rules are created and controlled
by the network administrator and can be precisely defined. These rules are used
to block access to the network from the outside, or deny access to the WAN from
within the network. The Router uses filtering rules to examine data packet
headers for specific information. Packets passing through the Router that do not
meet the criteria specified by the rule set are dropped.
In order to improve network security without severely limiting network
efficiency, it is important to carefully plan the sets of access rules. Effective
implementation of packet filtering requires detailed knowledge of network
services and communication protocols. An overly complicated filtering scheme
can adversely effect routing performance, while an inadequate set of rules may
needlessly compromise security.
Packet filtering can be used in conjunction with NAT, port redirection and proxy
servers to help provide basic firewall protection. However, these measures do not
address many security issues and should be used as only one part of an overall
network security strategy. It is important to remember that IP packet filtering
examines only the packet header and is not concerned with application
information. Therefore, packet filtering does not protect against higher-level
security threats that may operate at the application or other level.
Filtering rules can be precisely defined based upon source and destination IP
address, as well as port and protocol information. Up to twelve filter sets can be
used; each set contains up to seven filtering rules subsets. 
						

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Advanced Filtering and Firewall (Screen #1)
To define the filter rule sets, click on the Advanced Filtering and Firewall button
to bring up the first window. Choose Enable
 in the IP Filter 
pull-down menu
and click the OK
 button to enable IP filtering. Then click on the set number you
wish to configure to proceed to the next window.