Intermec MobileLAN 21 Series, Системное руководство

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MobileLAN access 21XX System Manual
4-14
About IP Tunnels
The physical boundary of a wireless network is usually defined by the presence of an IP
router. Multiple independent wireless networks may exist, each with its own LAN ID,
root access point, and set of wireless end devices. In this environment, an end device
can only operate within the limited coverage area of its own network and cannot roam
across IP subnet boundaries. However, using IP tunnel technology, end devices now can
roam across subnet boundaries. This technology is designed to safely and transparently
coexist with routed IP installations while supporting mobility for end devices. IP tunnels
do the following:
•
Enables access points on different subnets to belong to the same wireless network.
•
Supports transparent roaming of end devices between access points that are on
different subnets without losing network connections.
•
Supports end devices using both IP and other routable or nonroutable protocols.
The access point consists of a group of multiport Ethernet-to-wireless bridges. The IP
tunnel port uses a standard IP protocol called Generic Routing Encapsulation (GRE) to
encapsulate a frame. These encapsulated frames can use normal IP routing to pass
through IP routers. Unlike the physical Ethernet and radio ports, the IP tunnel port does
not have its own output connector. It is a logical port that provides IP encapsulation
services for frames that must be routed to reach their destinations. Once frames are
encapsulated, they are transmitted or received through a physical port.
In other words, IP tunnels use encapsulation to establish a virtual LAN segment through
IP routers. The virtual LAN segment includes the home IP subnet and logically extends
to include end devices attached to access points on remote IP subnets. An IP tunnel
becomes a branch in the spanning tree. Access points on remote subnets can be directly
connected to an IP tunnel or indirectly connected through another access point on a
remote subnet.