Packet filtering in connection-based switching networks

Details Packet filtering in connection-based switching networks Packet filtering in connection-based switching networks

1996-09-19

2003-01-21

Rao, Seema S (Department: 2661)

Multiplex communications

Pathfinding or routing

Combined circuit switching and packet switching

C370S395310, C370S401000, C370S404000, C370S230100

Reexamination Certificate

active

06510151

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to communication networks, and, more particularly to apparatus and methods for filtering packets in a connection-based switching network that includes a shared-media subnetwork.
BACKGROUND OF THE INVENTION
As businesses have realized the economic advantages of sharing expensive computer resources, cabling systems (including wireless cabling systems) have proliferated in order to enable the sharing of such resources over a computer network. A network for permitting this communication may be referred to as a local area network or “LAN.” LAN refers to an interconnection data network that is usually confined to a moderately-sized geographical area, such as a single office building or a campus area. Larger networks are often referred to as wide area networks or “WANs.”
Networks may be formed using a variety of different interconnection elements, such as unshielded twisted pair cables, shielded twisted pair cables, coaxial cable, fiber optic cable or even wireless interconnect elements. The configuration of these cabling elements, and the interfaces for the communication medium, may follow one (or more) of many topologies, such as star, ring or bus. In addition, a number of different protocols for accessing the networking medium have evolved. For example, the Institute of Electrical and Electronics Engineers, IEEE, has developed a number of standards for networks, including IEEE 802.3 relating to Ethernet buses using carrier sense multiple access and collision detection, IEEE 802.4 relating to token buses using token passing and IEEE 802.5 relating to token ring networks using token passing. The American National Standards Institute (ANSI) has also developed a standard for fiber distributed data interface (FDDI) using multiple token passing.
As demand has grown, communication networks have gotten bigger and bigger. Eventually, the number of stations on the network use up the available bandwidth for that network, or approach limits imposed by the physical medium employed. In addition, it is often desirable to combine two existing networks into one larger network. Accordingly, methods and apparatus for connecting two separate networks have developed. One such method involves the use of a bridge.
Generally, a “bridge” refers to a link between (at least) two networks. Thus, when a bridge receives information on one network, it may forward that information to the second network. In this fashion, two separate networks can be made to function as one larger network.
FIG. 1A
illustrates one example of networks being interconnected. A first network NW
1
is shown as a network cloud NW
1
. End station ES
1
is located within that network. Similarly, the figure illustrates a second network NW
2
containing a second end station ES
2
; a third network NW
3
containing a third end station ES
3
; and a fourth network NW
4
containing a fourth end station ES
4
.
In
FIG. 1A
, the four networks NW
1
, NW
2
, NW
3
and NW
4
, are interconnected using a shared media network F. (As discussed in more detail below, information on a shared media network is made available to all switches on that network.) The strategy for connecting networks NW
1
-NW
4
in the topology of
FIG. 1A
uses a “backbone.” That is, a separate network is disposed between each of the existing networks NW
1
-NW
4
. Communication traffic between the networks, therefore, is sent over the network backbone F. In the illustration, shared media network F is an FDDI token ring. Since shared media network F (or any of networks NW
1
-NW
4
) constitutes a communication network within a larger communication network, shared-media network F may also be referred to as a subnetwork.
Interconnections may be achieved using switches S
1
, S
2
, S
3
and S
4
. The switch S
1
may include two components. The FDDI components F
1
-F
4
process and manage communications over the FDDI ring F, according to methods known in the art. The bridging components B
1
-B
4
manage the bridging of traffic from the networks NW
1
-NW
4
to the FDDI ring F, and vice-versa.
Bridging strategies are well known in the art, and are the subject of a standard promulgated by the IEEE, IEEE 802.1, concerning transparent or self-learning bridges. A useful background discussion of bridges can be found in Radia Perlman, Interconnections:
Bridges and Routers,
Edison Wellesley Professional Computing Series, Reading, Mass. (1992). To aid in understanding the present invention, a discussion of transparent bridges follows. This discussion is not intended to limit the scope or application of the present invention and claims.
One possible strategy for connecting two networks with a bridging board would be for the bridging board to forward all communications (often referred to as “packets” or “data packets”—both of these terms, as used in the specification and the claims, are intended to include traditional data packets and their functional equivalents, such as “cells,” “datagrams,” or the like) to all other networks connected to that board. For example, whenever a communication is sent from end station ES
1
, that communication would be forwarded via the shared media subnetwork F to each of the other networks NW
2
, NW
3
and NW
4
, regardless of who is the intended recipient. In this fashion, the shared-media subnetwork F would serve to combine the four networks NW
1
-NW
4
as though they were only one network. Unfortunately, the duplication of every message sent on the network would quickly clog up the available bandwidth on each of the networks.
To address this problem, it would be possible to program each bridging board with the location of each station on each network. In this way, every communication could be routed to the appropriate network. This is a viable option as discussed below for connection-based networks; however, it may require replacement of existing network hardware, at additional expense.
Another alternative is to have a bridging board watch traffic across the board in order to learn the location of each end station, as communications are made over the network. In this fashion bridges could be simply plugged into networks and left on their own to learn the proper connections to be made. This type of bridge is often referred to as a “transparent” bridge or “self-learning” bridge.
FIG. 1B
illustrates an example of end station ES
1
sending a packet to end station ES
2
. Each packet of information includes a unique identifier that indicates the source station and destination station for the packet. In this example, the source address would be a unique address (such as a media access control, or “MAC” address) for ES
1
and the destination address is a unique identifier for ES
2
. In the example, the packet is first sent from network NW
1
to the backbone switch S
1
, as indicated at
12
a.
From this packet, bridging component B
1
learns that end station ES
1
is located off of its network port, as indicated in the first two columns of the table illustrated at T
1
.
A function of the bridging components B
1
-B
4
is to remove (i.e., refuse to forward or “filter”) data traffic that should not be sent to an attached network. In the present example, when bridging component B
1
determines that end station ES
1
lies off of its network port, it should not filter subsequent traffic to network NW
1
—if that traffic has a destination address corresponding to end station ES
1
. Accordingly, a filter entry of the table T
1
indicates that traffic to end station ES
1
should not be filtered.
Because the destination address of the packet (which corresponds to end station ES
2
) is not present in the table T
1
, bridging component B
1
forwards the packet to the FDDI ring F. As indicated at
12
b,
the FDDI component F
1
forwards the packet along the FDDI ring. Because the bridging component B
2
is not aware of where end station ES
2
is located, the bridging component B
2
forwards the packet onto network NW
2
, as indicated at
12
c.
In addition, bridging component B
2
learns from the source address for the packet that end s

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