Allied Telesis AT-WA7500 Comparing IP Tunnels to Mobile IP, Issue IP Tunneling Mobile IP, Igmp

Chapter 5: Configuring the Spanning Tree

Comparing IP Tunnels to Mobile IP

The AT-WA7500 and AT-WA7501 access points support IP tunneling, which allows end devices to roam across different subnets (routers) without having to change IP addresses. IP tunneling supports IETF RFC 1701 using GRE and the same encapsulation technique as mobile IP. IP tunnels technology is designed primarily to operate in local environments, where handheld or vehicle-mounted devices may move rapidly between access point coverage areas on a subnet (although it is possible to attach a geographically remote subnet through an IP tunnel).

The Internet Engineering Task Force developed RFC 2002, IP Mobility Support, commonly referred to as mobile IP, to provide mobility for IP hosts. Mobile IP is designed primarily to address the needs of wireless end devices that may move between geographically separated locations.

The two technologies are complimentary and may coexist. Both protocols use similar encapsulation to forward frames to or from end devices that have roamed away from a root IP subnet. The root access point functions much like a mobile IP home agent; an access point attached to the remote end of an IP tunnel functions much like a mobile IP foreign agent.

Table 46. IP Tunnels and Mobile IP Comparison

Issue	IP Tunneling	Mobile IP
Software compatibility	No changes are required to	Requires a mobile IP client
	existing IP software stacks in	software stack in end devices.
	end devices.
Addressing limitations for	Requires that end device IP	None.
IP end devices	addresses belong to the root
	IP subnet.
Security	Guest addresses are not	Mobile IP authentication is
	used. Data link security.	required for “guest” access to
		foreign subnets.
Roaming detection	Data link indications facilitate	Foreign agent
	fast roaming with no added	advertisements.
	broadcast traffic.
Roaming restrictions	Currently, roaming is limited to	None.
	a single network that may
	include multiple IP subnets.
Roaming support for non-	Configurable using IP filters.	None.
IP protocols
Scalability	No practical limitations using	Has no inherent limitations.
	IGMP.

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