Electrical computers and digital processing systems: multicomput – Computer-to-computer data addressing
Reexamination Certificate
2000-11-14
2002-11-26
Geckil, Mehmet B. (Department: 2152)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data addressing
C709S230000, C709S231000, C709S202000, C370S331000
Reexamination Certificate
active
06487605
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to Mobile IP network technology. More particularly, the invention relates to redundancy protocols and apparatus for protecting a Mobile IP system from failure due to the loss of a Home Agent (“HA”) or Foreign Agent (“FA”).
Mobile IP is a protocol which allows laptop computers or other mobile computer units (referred to as “Mobile Nodes” herein) to roam between various sub-networks at various locations—while maintaining internet and/or WAN connectivity. Without Mobile IP or related protocol, a Mobile Node would be unable to stay connected while roaming through various sub-networks. This is because the IP address required for any node to communicate over the internet is location specific. Each IP address has a field that specifies the particular sub-network on which the node resides. If a user desires to take a computer which is normally attached to one node and roam with it so that it passes through different sub-networks, it cannot use its home base IP address. As a. result, a business person traveling across the country cannot merely roam with his or her computer across geographically disparate network segments or wireless nodes while remaining connected over the internet. This is not an acceptable state-of-affairs in the age of portable computational devices.
To address this problem, the Mobile IP protocol has been developed and will soon be implemented. An implementation of Mobile IP is described in RFC 2002 of the Network Working Group, C. Perkins, Ed., October 1996. Mobile IP is also described in the text “Mobile IP Unplugged” by J. Solomon, Prentice Hall. Both of these references are incorporated herein by reference in their entireties and for all purposes.
The Mobile IP process and environment are illustrated in FIG.
1
A. As shown there, a Mobile IP environment
2
includes the internet (or a WAN)
4
over which a Mobile Node
6
can communicate remotely via mediation by a Home Agent
8
and a Foreign Agent
10
. Typically, the Home Agent and Foreign Agent are routers or other network connection devices performing appropriate Mobile IP functions as implemented by software, hardware, and/or firmware. A particular Mobile Node (e.g., a laptop computer) plugged into its home network segment connects with the internet through its designated Home Agent. When such Mobile Node roams, it communicates via the internet through an available Foreign Agent. Presumably, there are many Foreign Agents available at geographically disparate locations to allow wide spread internet connection via the Mobile IP protocol. Note that it is also possible for the Mobile Node to register directly with its Home Agent.
As shown in
FIG. 1A
, Mobile Node
6
normally resides on (or is “based at”) a network segment
12
which allows its network entities to communicate over the internet
4
through Home Agent
8
(an appropriately configured router denoted R
2
). Note that Home Agent
8
need not directly connect to the internet. For example, as shown in
FIG. 1A
, it may be connected through another router (a router R
1
in this case). Router R
1
may, in turn, connect one or more other routers (e.g., a router R
3
) with the internet.
Now, suppose that Mobile Node
6
is removed from its home base network segment
12
and roams a remote network segment
14
. Network segment
14
may include various other nodes such as a PC
16
. The nodes on network segment
14
communicate with the internet through a router which doubles as Foreign Agent
10
. Mobile Node
6
may identify Foreign Agent
10
through various solicitations and advertisements which form part of the Mobile IP protocol. When Mobile Node
6
engages with network segment
14
, Foreign Agent
10
relays a registration request to Home Agent
8
(as indicated by the dotted line “Registration”). The Home and Foreign Agents may then negotiate the conditions of the Mobile Node's attachment to Foreign Agent
10
. For example, the attachment may be limited to a period of time, such as two hours. When the negotiation is successfully completed, Home Agent
8
updates an internal “mobility binding table” which specifies the Foreign Agent's IP address in association with the identity of Mobile Node
6
. Further, the Foreign Agent
10
updates an internal “visitor table” which specifies the Mobile Node address, Home Agent address, etc. In effect, the Mobile Node's home base IP address (associated with segment
12
) has been shifted to the Foreign Agent's IP address (associated with segment
14
).
Now, suppose that Mobile Node
6
wishes to send a message to a corresponding node
18
from its new location. An output message from the Mobile Node is then packetized and forwarded through Foreign Agent
10
over the internet
4
and to corresponding node
18
(as indicated by the dotted line “packet from MN”) according to a standard internet protocol. If corresponding node
18
wishes to send a message to Mobile Node—whether in reply to a message from the Mobile Node of for any other reason—it addresses that message to the IP address of Mobile Node
6
on sub-network
12
. The packets of that message are then forwarded over the internet
4
and to router R
1
and ultimately to Home Agent
8
as indicated by the dotted line (“packet to MN(
1
)”). From its mobility binding table, Home Agent
8
recognizes that Mobile Node
6
is no longer attached to network segment
12
. It then encapsulates the packets from corresponding node
18
(which are addressed to Mobile Node
6
on network segment
12
) according to a Mobile IP protocol and forwards these encapsulated packets to a care of address for Mobile Node
6
as shown by the dotted line (“packet to MN(
2
)”). The C.O. address is the IP address of Foreign Agent
10
. Foreign Agent
10
then strips the encapsulation and forwards the message to Mobile Node
6
on sub-network
14
. The packet forwarding mechanism implemented by the Home and Foreign Agents is often referred to as “tunneling.”
FIG. 1B
illustrates a significant problem with the Mobile IP system
2
. If Home Agent
8
fails or otherwise become inoperative (due to a power failure, rebooting, scheduled maintenance. etc.), Mobile Node
6
is left without the ability to (1) receive new internet messages addressed to it at network segment
12
and (2) register with other Foreign Agents. In effect, Mobile Node
6
is cut-off from internet connection when Home Agent
8
goes down. This problem may extend to other Mobile Nodes supported by Home Agent
8
. Often, a given Home Agent will be responsible for servicing numerous Mobile Nodes which may be based at sub-network
12
.
As shown in
FIG. 1B
, when Home Agent
8
fails, not only is network segment
12
disconnected from the internet, but Mobile Nodes at remote locations are also blocked from the registration and packet receipt functions of Mobile IP. In some networks, there may be other routers connecting segment
12
to the internet. Such additional routers would allow fixed hosts on the segment to maintain their internet connections but would not allow remote access to Mobile Nodes. Similarly, if Foreign Agent
10
should fail, all Mobile Nodes visiting sub-network
14
lose connections, even though there may be other routers on that sub-network.
A redundancy protocol known as Hot Standby Router Protocol (“HSRP”) is widely used to back up primary routers for a network segment. In HSRP, a “standby” or “secondary” router is designated as the back-up to an “active” or “primary” router. The standby router is linked to the network segment or segments serviced by the active router. The active and standby routers share a “virtual IP address” and possibly a “virtual Media Access Control (MAC) address.” All internet communication to and from the relevant sub-network employs the virtual IP and MAC addresses. At any given time, the active router is the only router adopting the virtual addresses. Then, if the active router should cease operation for any reason, the standby router immediately takes over its load (by adopting the virtual address
Beyer Weaver & Thomas LLP
Cisco Technology Inc.
Geckil Mehmet B.
Plieto Beatriz
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