User manual

AP User Manual January 2004
Software Release 4.1
Identification of Subnet Class
Subnet masks are not shipped in the IP packet. The packet contains only the 32-bit IP address of
the destination. For this reason, information devices rely on assumption to distinguish between
• the portion of the IP address that identifies the network address
• the portion of the IP address that identifies the host.
IP systems developed a form of logic to make this determination:
• Class A network addresses always have the first bit of the IP address set to 0.
• Class B network addresses always have their first bit set to 1 and their second bit
set to 0.
• Class C network addresses always have their first two bits set to 1 and the third bit
set to 0.
With this logic, an information device can identify the subnet mask to apply to the IP address and
where to route the data.
6.2 DYNAMIC OR STATIC ADDRESSING
For any computer to communicate with a Canopy module, the computer must be configured to
either
• use DHCP (Dynamic Host Configuration Protocol). In this case, when not connected to
the network, the computer derives an IP address on the 169.254 network within two
minutes.
• have an assigned static IP address (for example, 169.254.1.5) on the 169.254
network.
NOTE: If an IP address that is set in the AP is not the 169.254.x.x network address,
then the network operator must assign the computer a static IP address in the same
subnet.
6.2.1 When a DHCP Server is Not Found
The following is a synopsis of an Internet Draft available at
http://www.ietf.org/internet-drafts/draft-ietf-zeroconf-ipv4-linklocal-05.txt. This draft describes how
Microsoft and Apple operating systems react when a DHCP server is not found on the network.
To operate on a network, a computer requires an IP address, a subnet mask, and possibly a
gateway address. Either a DHCP server automatically assigns this configuration information to a
computer on a network or an operator must input these items.
When a computer is brought online and a DHCP server is not accessible (such as when the server
is down or the computer is not plugged into the network), Microsoft and Apple operating systems
default to an IP address of 169.254.x.x and a subnet mask of 255.255.0.0 (169.254/16).
6.3 AP MODULE ADDRESS ASSIGNMENT
Each AP requires an IP address on the network. This IP address is for only management purposes.
For security, the AP should be either
• not assigned a routable IP address.
• assigned a routable IP address only if a firewall is present to protect the AP.
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