16
Introduction
•
Session Rate Limiting:
Reduces the risk of “Denial of Service” attacks by allowing administrators to limit the
number of sessions one user can take over a given time period and, if necessary, then block malicious users. See
Session Rate Limiting
for details.
•
Session Termination Redirect:
Once connected to the Public-access network, the AP will automatically direct the
customer to a Web site for local or personalized services, or to establish an account and pay for services though its
Home Page Redirect functionality. In addition, the AP also provides pre and post authentication redirects as well
as one at session termination. See
Home Page Redirection (HPR)
.
•
Smart Client Support:
The AP supports authentication mechanisms used by Smart Clients by companies such as
Adjungo Networks, Boingo Wireless, GRIC and iPass. See
Smart Client
for details.
Dynamic Address Translation (DAT)
Dynamic Address Translation (DAT) is a technique that eliminates IP configuration issues and the associated
complaints and support requests from subscribers.
Without DAT, a subscriber will typically need to change the following settings (twice -- once to join the hotspot network
and then set them back again to rejoin the user’s home network):
•
IP Address
•
Subnet Mask
•
Default Gateway Address
•
DNS Server Addresses
•
Web browser’s proxy settings
•
Outgoing mail server settings
DAT eliminates the need for subscribers to change any of these settings. The AP-2500 automatically redirects
subscriber messages to the appropriate location. DAT even works if a user’s wireless card is configured with static
IP settings.
One of the key features of DAT is a technique known as
Network Address Translation (NAT)
. NAT is an Internet
standard that allows a device (like the AP-2500) to use a single public IP address to provide Internet connectivity to
multiple devices (which would otherwise each need to have its own public IP address to communicate with the
network). The AP-2500 uses NAT for clients that are configured to obtain an IP address automatically from a DHCP
server (which is the typical configuration for hotspot users) and for clients with “misconfigured” static IP addresses
(that is, addresses that are not valid on the AP’s local IP network).
When performing NAT, an AP-2500 uses two IP addresses. One IP address is assigned by your ISP and is valid on
the Internet. This is known as a
public
or
routable
IP address.
The second IP address assigned to the AP is its
private
IP Address. This address is not valid on the Internet. The
Internet community has reserved several address ranges for private networks, including 10.0.0.0 and 192.168.0.0. By
default, the AP assigns itself a private IP address of 10.0.0.4. It also acts as a DHCP server to assign IP address in
that same private IP range to wireless subscribers.
When the AP receives traffic from Client 1, it modifies the packet header so Client 1’s private IP address (10.0.0.15)
becomes the AP’s public IP address (205.23.45.12). Likewise, the AP performs the same function for traffic from
Client 2.
The AP differentiates between its clients by specifying different UDP and TCP port numbers for traffic that originates
from different clients. When the AP receives traffic from the Internet, the AP can determine to which client the traffic is
intended based on the port numbers in use.
The NAT technique used by the AP-2500 is known by many names including
many-to-one NAT
(that is, many private
IP addresses mapped to one public IP address) and
Network Address Port Translation (NAPT)
(due to the AP’s use
of port numbers to differentiate clients). For more information on NAT, see RFC 3022 at
http://www.rfc-editor.org/
.
Networking Features
The AP-2500 provides wireless access to the Internet for hotspot subscribers. This means that your customers can
surf the Internet and send e-mails from anywhere within range of the Access Point without having to install extra wires
or cabling.
