WO1998026555A1

WO1998026555A1 - Method and apparatus for dynamic packet filter assignment

Info

Publication number: WO1998026555A1
Application number: PCT/US1997/022561
Authority: WO
Inventors: Sanjay R. Radia; Swee B. Lim; Panagiotis Tsirigotis; Thomas K. Wong; Robert J. Goedman; Michael W. Patrick
Original assignee: Sun Microsystems, Inc.; Motorola Inc.
Priority date: 1996-12-09
Filing date: 1997-12-08
Publication date: 1998-06-18
Also published as: JP2001506093A; DE69734019T2; EP1013045A1; DE69734019D1; US5848233A; EP1013045B1

Abstract

The present invention includes a method and apparatus for filtering IP packets based on events within a computer network. More specifically, the present invention includes a services management system, or SMS. The SMS manages network connections between a series of client systems and a router. An access network control server (ANCS) manages the configuration of the router. The SMS monitors activities or events that occur within the network. In response to these events, the SMS dynamically downloads filtering profiles to the ANCS. The ANCS then uses the downloaded filtering profiles to reconfigure the router. The router then uses the filtering rules to selectively discard or forward IP packets received from the client systems.

Description

Method and Apparatus for Dynamic Packet Filter Assignment

FIELD OF THE INVENTION

The present invention relates generally to security in computer networks.

More specifically, the present invention is a method and apparatus that allows IP

packets within a network to be selectively filtered based on events within the

network.

BACKGROUND OF THE INVENTION

Recent years have witnessed an explosive growth in the use of computer

networks. In fact, the use of computer networks to connect disparate computer

systems around the world has become a routine and accepted fact. One result of the

ever-increasing use of computer networks is an ever-increasing need for security

systems.

Computer networks that use the Internet protocol are commonly referred to as

IP networks. Within IP networks, messages are sent and received using discrete

quanta known as "packets." Each packet includes a header and a body. Messages

are sent by partitioning the message and including each portion of the partitioned

message in the body of a packet. The packets are sent over the IP network and

reassembled into the message at the receiving system.

Packet filters are programs that examine the data included in packet headers

and discard packets that appear to present a threat to network security. For

example, assume that a company uses a router to link its internal intranet with an

external network, such as the Internet. Typically, a router used in this configuration

will inspect the header of each received packet to determine the address of the

system sending the packet. Clearly, in this case, packets that arrive from the Internet but that have source addresses that correspond to addresses of systems within the

company intranet are suspect. A packet filter included in the router would, therefore,

discard packets of this type. Filtering can be based on the target of the packet, the

higher level protocol or other packet content.

In general, the use of packet filters has been found to be an effective and

relatively simple technique for increasing security within computer networks.

Unfortunately, there are also some disadvantages associated with traditional packet

filtering techniques. One such disadvantage results from the static nature of

traditional packet filtering systems. It has generally been the case that packet

filtering systems are configured using a fixed set of filtering rules. These rules are

then used to filter packets within the network and remain in effect until the packet

filtering system is reconfigured. Since reconfiguration of the packet filtering system is

relatively rare, the particular filtering rules that are in effect within a particular

network are generally of a fixed and static nature.

for example, in the scenario, the access control rules are fairly static.

External packets (packets from the Internet) are allowed very restricted access.

Internal packets (from within the Internet) are allowed fairly static access to certain

parts of the internal network. As machines are added/removed or moved then the

filtering rules may be changed. Once further minimize the changes to filtering rules

by using subnetwork fields in the filtering rules. E.g. instead of saying that access is

allowed to a host with address xyz, one says that access is allowed to hosts with

address xy^*. This allows the target machine to be moved within the subnetwork or

even new ones to be added. Now consider a more dynamic system where one wants to control access

based on certain events such as the user's connected to the network. For example,

an internet service provider (ISP) may have users who connect, login, logoff and

disconnect to its network over time using telephone or able modems. The ISP would

like to control access to this dynamically changing set of users. Furthermore,

different users may be allowed different access based on who the user is and what

set of services the user as subscribed. As a result, the quality of packet filtering

provided by traditional packet filtering systems is often less than optimal.

SUMMARY OF THE INVENTION A preferred embodiment of the present invention includes a method and

apparatus for filtering IP packets based on events within the network. More

specifically, a preferred environment for the present invention is a computer network

that includes a series of client systems and a router. An access network control

server (ANCS) controls configuration of the router and the components of the

network that forward packets from the client systems. A services management

system (SMS), dynamically reconfigures the ANCS. The network also includes a

DHCP server that implements the Dynamic Host Configuration Protocol (DHCP)

defined in Internet RFC 1541. The client systems, which are typically personal

computers using cable modems, connect to the router. As part of the connection

process, each client system receives a dynamically allocated IP address from the

DHCP server.

The SMS maintains a series of filtering profiles, each of which includes one or

more of filtering rules. The SMS sets a default filter sequence for the newly

connected client system by downloading the sequence by the SMS to the ANCS. The ANCS uses the rules included in the downloaded login filtering profile sequence

to establish a packet filter for IP packets originating from the newly connected client

system. Whenever the ANCS establishes a new packet filter for a client system, any

packet filter previously established for the same client system is discarded. The

packet filter is established by reconfiguring the components of the network that

forward packets originating at the client system, such as the router or the modem

connected to the client system. Subsequently, the packet filter uses the rules of the

login filtering profile sequence to selectively forward or discard IP packets originating

from the client system. This filtering sequence will allow newly connected client

systems to perform login, but nothing else.

In the above description, we have set a default profile called the default login

profile. The default login profile is a static profile that applies to ALL newly

connected client systems. This way the SMS does not need to be aware as new

client systems are connected.

One may also consider setting the default profile to a null profile and for each

client system as the client system connects; for example, since a client system that

connects may do a DHCP operation, this event can trigger the SMS to set the login

profile for the newly connected computer.

A preferred embodiment of the present invention also generates or selects

filtering profiles for users. With the login filtering profile sequence in place, a user

can use the newly connected client system to login to the network. The user login is

monitored by the SMS. If the user login is successful, the SMS selects or generates

a user filtering profile sequence. The user filtering profile sequence is then

downloaded by the SMS to the ANCS. The ANCS uses the rules included in the downloaded login filtering profile sequence to establish a new packet filter for IP

packets originating from the newly logged in client system. The new packet filter is

established by reconfiguring the components of the network to replace the packet

filter established for the login filtering profile. Subsequently, the new packet filter

uses the rules of the user filtering profile sequence to selectively forward or discard

IP packets originating from the client system.

Note that in the above description we have used the events of connecting a

client system, logging in, and logging out as events that trigger the SMS to change

filtering rules. In other environments other events may be used to trigger the setting

of filter rules.

We have described the SMS as a single computer system that sets the filter

rules. One may consider the SMS to be a set of machines that collectively set filter

rules in different part of the computer network.

Similarly, we have described the ANCS as a single computer but it may also

be a set of computers that can be used to control the router and the components of

the network that forwards packets from client systems.

In accordance with the purpose of the invention, as embodied and broadly

described herein, the present invention is a method for filtering IP packets in a

computer network that includes one or more client systems, the method comprising

the steps, performed by one or more computer systems, of: detecting an event

associated with one of the client systems, selecting one or more filtering rules based

on the type of event detected, and establishing a packet filter in the computer

network, the packet filter using the selected rules to selectively discard packets

originating at the client system associated with the detected event. In further accordance with the purpose of the invention, as embodied and

broadly described herein, the present invention is an apparatus for filtering IP

packets in a computer network that includes one or more client systems, the

apparatus comprising: a first portion configured to cause a computer system to

detect an event associated with one of the client systems, a second portion

configured to cause a computer system to provide one or more filtering rules based

on the type of event detected, and a third portion configured to cause a computer

system to establish a packet filter in the computer network, the packet filter using the

selected rules to selectively discard packets originating at the client system

associated with the detected event.

Advantages of the invention will be set forth, in part, in the description that

follows and, in part, will be understood by those skilled in the art from the description

or may be learned by practice of the invention. The advantages of the invention will

be realized and attained by means of the elements and combinations particularly

pointed out in the appended claims and equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part

of this specification, illustrate several embodiments of the invention and, together

with the description, serve to explain the principles of the invention.

Figure 1 is a block diagram of a computer network shown as a representative

environment for a preferred embodiment of the present invention.

Figure 2 is a block diagram of an access network control server as used by a

preferred embodiment of the present invention. Figure 3 is a block diagram of a services management system as used by a

preferred embodiment of the present invention.

Figure 4 is a block diagram of a filtering profile as used in a preferred

embodiment of the present invention.

Figure 5 is a block diagram of a filtering rule as used in a preferred

embodiment of the present invention.

Figure 6 is a flowchart showing an overview of the steps associated with the

use of the filtering profiles of a preferred embodiment of the present invention.

Figure 7 is a flowchart showing the steps associated with a preferred

embodiment of a method for user login to a computer network.

Figures 8a through 8d are block diagrams showing filtering profiles

associated with a preferred method for user login to a computer network.

Figure 9 is a flowchart showing the steps associated with a preferred

embodiment of a method for allocation of privileges to a user in a computer network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to preferred embodiments of the present

invention, examples of which are illustrated in the accompanying drawings.

Wherever possible, the same reference numbers will be used throughout the

drawings to refer to the same or like parts.

In Figure 1 , a computer network 100 is shown as a representative

environment for the present invention. Structurally, computer network 100 includes a

series of client systems 102, of which client systems 102a through 102f are

representative. Each client system 102 may be selected from a range of differing

devices including, but not limited to the personal computers shown in Figure 1. Preferably, each client system 102 is limited to a single user at any given time. A

cable modem 104 is connected to each client system 102. Each cable modem 104 is

connected, in turn, to a cable router 106. The use of cable router 106 and cable

modems 104 is also intended to be exemplary and it should be appreciated that

other networking technologies and topologies are equally practical. It should also be

appreciated that a number of different cable modems and cable routers are available

from various manufactures In particular, cable modem 104 can be a CyberSUFR

cable modem and cable router 106 can be a CableMASTR cable router, both

supplied by Motorola, Inc.

Network 100 also includes a series of server systems 108, of which server

systems 108a through 108a are representative. Each server system 108 is

connected to cable router 106. Generally, server systems 108 are intended to

represent the broad range of server systems that may be found within computer

networks. A DHCP server system 110 is also included in computer network 100 and

connected to cable router 106. DHCP server system 110 is a computer or other

system that implements Dynamic Host Configuration Protocol (DHCP) defined in

Internet RFC 1541. Functionally, DHCP server system 110 provides for allocation of

IP addresses within network 100. When client systems 102 initially connect to cable

router 106, each client system 102 requests and receives an IP address from DHCP

server system 110. Although Figure 1 shows only a single DHCP server system 110,

it is to be understood that additional DHCP server systems 110 may be used without

departing from the spirit of the present invention. Computer network 100 also includes an access network control server

(ANCS) 112 and a services management system (SMS) 114. Both ANCS 112 and

SMS 114 are connected to cable router 106. ANCS 112 is shown in more detail in

Figure 2 to include a computer system 202 that, in turn, includes a processor, or

processors 204, and a memory 206. An input device 208 and an output device 210

are connected to the computer system 202 and represent a wide range of varying

I/O devices such as disk drives, keyboards, modems, network adapters, printers and

displays. A disk drive 212, of any suitable disk drive type, is shown connected to

computer system 202. An ANCS process 214 is shown to be resident in memory

206 of computer system 202.

SMS 114 is shown in more detail in Figure 3 to include a computer system

302 that, in turn, includes a processor, or processors 304, and a memory 306. An

input device 308 and an output device 310 are connected to the computer system

302 and represent a wide range of varying I/O devices such as disk drives,

keyboards, modems, network adapters, printers and displays. A disk drive 312, of

any suitable disk drive type, is shown connected to computer system 302. An SMS

process 314 and a filtering profile database 316 are shown to be resident in memory

306 of computer system 302. In Figure 1 , ANCS 112 and SMS 114 are shown as

separate entities. It should be appreciated, however, that the present invention

specifically anticipates that ANCS 112 and SMS 114 may be implemented using a

single computer system that includes ANCS process 214, SMS process 314 and

filtering profile database 316.

The filtering profile database 316 of SMS 114 includes a set of filtering

profiles of the type shown in Figure 4 and generally designated 400. Filtering profile 400 includes a profile id 402 and a series of filtering rules, of which filtering rules

404a through 404c are representative. The profile id 402 is used by SMS 114 and

ANCS 112 as an internal identifier for the filtering profile 400. The filtering rules 404

included in a filtering profile 400 are better understood by reference to Figure 5. In

Figure 5, it may be seen that each filtering rule 404 includes an action 500. Action

500 specifies the disposition of IP packets that match by a particular filtering rule

404. In particular, action 500 may indicate that a matched IP packet will be

forwarded, or that a matched IP packet will be discarded. Filtering rule 404 also

includes a destination IP address 502 and a destination IP mask 504. Destination IP

address 502 corresponds to the destination address included in the header of an IP

packet. Destination IP mask 504 is similar to destination IP address 502 but

corresponds to a range of destination addresses. To match a particular filtering rule

404, an IP packet must either have a destination address that matches the

destination address 502 included in the filtering rule 404 or have a destination

address that is covered by the destination address mask 504 of the filtering rule 404.

Filtering rule 404 also includes a protocol type 506. Protocol type 506

corresponds to the protocol type of an IP packet. Thus, the protocol type 506 of

each filtering rule 404 has a value that corresponds to an IP packet type, such as

TCP, UDP, ICMP, etc. To match a particular filtering rule 404, an IP packet must

have a protocol type that matches the protocol type 506 included in the filtering rule

404

Finally, for the embodiment shown, filtering rule 404 includes a starting port

number 508 and an ending port number 510. Starting port number 508 and ending

port number 510 define a range of port numbers of the type used by certain protocols, such as UDP and TCP. To match a particular filtering rule 404, an IP

packet of one of these types must have a port number that falls within the range

defined by starting port number 508 and ending port number 510.

The use of filtering profiles 400 by the present invention is shown generally in

Figure 6. In step 600 of Figure 6, SMS 114 generates a filtering profile 400. For the

purposes of illustration, it may be assumed that the filtering profile 400 is intended to

allow client system 102b to send UDP packets to port 63 of server system 108c.

Therefore, the filtering profile 400 generated in step 600 includes a single filtering

rule 404. The single filtering rule 404 includes an action 500 indicating that IP

packets that match the filtering rule 404 should be forwarded. Additionally, the

filtering rule 404 includes a destination address 502 that corresponds to the IP

address of server system 108c. The destination address mask 504 of filtering rule

404 is set to 255.255.255.255 (255.255.255.255 matches all IP addresses) and the

protocol type 506 of filtering rule 404 is set to UDP. Finally, the starting port number

508 and ending port number 510 of filtering rule 404 are both set to 63.

In step 602 of method 600, the filtering profile 400 is downloaded by the SMS

114 to the ANCS 112. At the same time, the SMS 114 also passes the IP address of

client system 102b to the ANCS 112. In step 604, the ANCS 112 uses the single

filtering rule 404 included in the filtering profile 400 to establish a packet filter for IP

packets originating from the client system 102b. The packet filter is established by

reconfiguring one or more of the components of the network 100 that forward

packets originating at the client system 102b. For example, in some cases the

packet filter may be established by reconfiguring the modem 104b connected to client system 102. Alternatively, the packet filter may be established by reconfiguring

router 106.

In step 606, the packet filter established by the ANCS 112 in step 604 is used

to filter packets that originate from the client system 102b. More specifically, each

packet that originates from client system 102b is examined. Packets that do not

include a destination address that corresponds to server system 108c are discarded.

Likewise packets that do not have a protocol type of UDP or a port number of 63 are

discarded.

A more complete example of the use of filtering profiles 400 by the present

invention is shown as method 700 of Figure 7. Method 700 includes step performed

by SMS 114 and ANCS 112. For convenience, these steps are grouped into an SMS

context 702 and an ANCS context 704. Method 700 begins with step 706 where

SMS 114 waits for the allocation of an IP address to a client system 102. More

specifically, for a preferred embodiment of network 100, power-on or reset of a client

system 102 is followed by connection of the client system 102 to router 106. As part

of this connection, the connecting client system 102 requests and receives a

dynamically allocated IP address from DHCP server 110. This allocation requires

that a number of messages pass between DHCP server 110 and the client system

102 requesting a new IP address. The last of these messages is a DHCPACK

message sent by the DHCP server 110 to the client system 102. To monitor the

allocation of IP addresses, SMS 114 monitors DHCP messages within network 100.

Step 706 corresponds, in a general sense, to the methods and procedures that are

executed by SMS 114 to wait for and detect DHCPACK messages within network

100. In step 708, SMS 114 generates a sequence of one or more "login" filtering

profiles 400 for the newly connected client system 102. Functionally, the purpose of

the login filtering profiles 400 is to restrict the type of IP packets that may originate at

the newly connected client system 102. Specifically, only the packet types that are

required for a user to login to network 100 are allowed. Generally, the type of IP

packets required for a user login will vary between different networks. For network

100, however, it may be assumed that four filtering profiles 400 are generated in

step 708.

The first of the four login filtering profiles 400 forwards packets associated

with DHCP lease renewal. More specifically, in systems that use the DHCP protocol

for allocation of IP addresses, each IP address is allocated for a finite period of time.

Systems that do not renew their IP address leases may lose their allocated IP

addresses. Therefore, the first login filtering profile 400 allows passage of IP packets

from the newly connected client system 102 to the DHCP server 110 for the purpose

of DHCP lease renewal. Preferably, the first filtering profile 400 includes a single

filtering rule 404 of the form shown in Figure 8a.

More specifically, and as shown in Figure 8a, the single filtering rule 404 for

DHCP lease renewal includes an action 500 that indicates that IP packets that

match the filtering rule 404 should be forwarded. Filtering rule 404 also includes a

destination address 502 that corresponds to the IP address of the DHCP server 110

and a destination address mask 504 of 255.255.255.255. As a result, only IP

packets directed at DHCP server 110 match filtering rule 404. A protocol type of

UDP is specified by protocol type 506 of filtering rule 404. Finally, beginning port number 508 and ending port number 510 are both set to "67" corresponding to the

standard port used for DHCP messages.

The second of the login filtering profiles 400 forwards packets associated with

DNS (domain name service) address resolution. More specifically, in systems that

use the DNS protocol, symbolic names are translated to IP address by a DNS server

system. Client systems 102 request translations of symbolic names by sending

messages to their DNS servers. Therefore, the second login filtering profile 400

allows passage of IP packets from the newly connected client system 102 to a DNS

server system (DNS server system not shown).

Preferably, the second filtering profile 400 includes a single filtering rule 404

of the form shown in Figure 8b. More specifically, and as shown in Figure 8b, the

single filtering rule 404 for DNS name resolution includes an action 500 that

indicates that IP packets that match the filtering rule 404 should be forwarded.

Filtering rule 404 also includes a destination address 502 that corresponds to the IP

address of a DNS server system and a destination address mask 504 of

255.255.255.255. As a result, only IP packets directed at the DNS server system

match filtering rule 404. A protocol type of UDP is specified by protocol type 506 of

filtering rule 404. Finally, beginning port number 508 and ending port number 510

are both set to 53 corresponding to the standard port used for DNS messages.

For a preferred embodiment of network 100, user logins are handled by

downloading small, specifically tailored applications, known as "login applets," to

client systems 102. The login applets are downloaded from a server system, such as

server system 108, or in some cases, from SMS 114. To allow the login applet to be

downloaded, the third of the login filtering profiles 400 forwards packets associated with a request for login applet download. Preferably, the third filtering profile 400

includes one filtering rule 404 for each server from which the login applet may be

downloaded. More specifically, and as shown in Figure 8c, the filtering rule 404 for

login applet download includes an action 500 that indicates that IP packets that

match the filtering rule 404 should be forwarded. Each filtering rule 404 also includes

a destination address 502 that corresponds to the IP address of a server system

from which the login applet may be downloaded. The destination address mask of

filtering rule 404 is set to 255.255.255.255.The protocol type 506, beginning port

number 508 and ending port number 510 of filtering rule 404 are all set to values

known by SMS 114 to be appropriate for the download of the login applet.

In the described embodiment of the network 100, the login applet

communicates with a login server such as SMS 114. To enable this communication,

the fourth of the login filtering profiles 400 forwards packets associated with login

applet communication. Preferably, the fourth filtering profile 400 includes one filtering

rule 404 for each login server such as SMS 114. More specifically, and as shown in

Figure 8d, the filtering rule 404 for login applet communication includes an action

500 that indicates that IP packets that match the filtering rule 404 should be

forwarded. Filtering rule 404 also includes a destination address 502 that

corresponds to the IP address of a login server such as SMS 114. The destination

address mask of filtering rule 404 is set to 255.255.255.255. The protocol type 506,

beginning port number 508 and ending port number 510 of filtering rule 404 are all

set to values known by SMS 114 to be appropriate for login applet communication.

In the preceding paragraphs, a sequence of four filtering profiles 400 has

been described. It may be appreciated from the preceding paragraphs that each of the four filtering profiles 400 is generally applicable to enable login processing for

any of the client systems 102. Because of the general applicability of the four

filtering profiles 400, it is preferable for step 708 to generate these filtering profiles

400 using a standardized template making only minor modifications, if necessary, for

each client system 102.

Step 708 is followed by step 710 where the sequence of four filtering profiles

400 is downloaded by SMS 114 to ANCS 112. At the same time, the IP address of

the newly connected client system 102 (for which the sequence of four filtering

profiles 400 was generated) is passed by the SMS 114 to the ANCS 112. In the

following step, the ANCS 112 uses each of the filtering rules 404 included in the

sequence of four filtering profiles 400 to establish a packet filter for IP packets

originating from the newly connected client system 102. The packet filter is

established by reconfiguring one or more of the components of the network 100 that

forward packets originating at the newly connected client system 102. For example,

in some cases, the packet filter may be established by reconfiguring the modem 104

connected to client system 102. Alternatively, the packet filter may be established by

reconfiguring router 106. Preferably, ANCS 112 reconfigures the network

components using a protocol that is generally applicable to components of network

100, such as the simple network management protocol (SNMP). Subsequently, the

packet filter established by the ANCS 112 is used to filter IP packets that originate

from the client system 102, allowing packet types generally associated with the login

of a user to network 100.

A second example of the use of filtering profiles 400 by the present invention

is shown as method 900 of Figure 9. Method 900 includes step performed by SMS 114 and ANCS 112. For convenience, these steps are grouped into an SMS context

902 and an ANCS context 904. Method 900 begins with step 906 where SMS 114

waits for a user login. More specifically, as discussed with regard to method 700, for

a preferred embodiment of network 100, users login to network 100 using a login

applet that communicates with a login server, such as SMS 114. Step 114

corresponds, in a general fashion, to the methods and procedures that are executed

by SMS 114 to wait for the login of a user to network 100.

In step 908, which follows, a sequence of filtering profiles 400 associated with

the user are retrieved, by SMS 114, from filtering profile database 316. In general, it

may be appreciated that various users of network 100 will have varying types of

allowed access. As a result, different network users will require different filtering

profiles 400. Generally, these filtering profiles 400 are defined separately for each

user using either automatic or manual generation techniques. For the present

invention, these filtering profiles 400 are preferably maintained in filtering profile

database 316 and retrieved using the identity of the particular user. Step 908

corresponds to the methods and procedures that are executed by SMS 114 to

retrieve the filtering profiles 400 associated with the user from the filtering profile

database 316.

Step 908 is followed by step 910 where the sequence of user filtering profiles

400 is downloaded by SMS 114 to ANCS 112. At the same time, the IP address of

the client system 102 acting as a host for the user is passed by the SMS 114 to the

ANCS 112. In the following step, the ANCS 112 uses each of the filtering rules 404

included in the sequence of user filtering profiles 400 to establish a packet filter for

IP packets originating from the client system 102 acting as a host for the user. The packet filter is established by reconfiguring one or more of the components of the

network 100 that forward packets originating at the client system 102 acting as a

host for the user. For example, in some cases, the packet filter may be established

by reconfiguring the modem 104 connected to client system 102. Alternatively, the

packet filter may be established by reconfiguring router 106. Preferably, ANCS 112

reconfigures the network components using a protocol that is generally applicable to

components of network 100, such as the simple network management protocol

(SNMP). Subsequently, the packet filter established by the ANCS 112 is used to

filter IP packets that originate from the client system 102 acting as a host for the

user, allowing the packets that are associated with the network privileges of the

user.

Although not shown, it may be appreciated that the network 100 may be

reconfigured to reestablish a default state after the user logs out from the client

system 102. Other embodiments will be apparent to those skilled in the art from

consideration of the specification and practice of the invention disclosed herein. It is

intended that the specification and examples be considered as exemplary only, with

a true scope of the invention being indicated by the following claims and equivalents.

Claims

WHAT IS CLAIMED IS:

1. A method for filtering IP packets in a computer network that includes

one or more client systems, the method comprising the steps, performed by one or

more computer systems, of:

detecting an event associated with one of the client systems;

selecting one or more filtering rules based on the type of event

detected; and

establishing a packet filter in the computer network, the packet filter

using the selected rules to selectively discard packets originating at the client

system associated with the detected event.

2. A method as recited in claim 1 wherein the detected event is the

assignment of an IP address to the client system.

3. A method as recited in claim 1 wherein the detected event is the login

of a user using the client system associated with the detected event

4. A method as recited in claim 1 wherein the computer network includes

a router and wherein the step of establishing a packet filter includes the step of

reconfiguring the router to selectively discard packets originating at the client system

associated with the detected event.

5. A method as recited in claim 1 wherein the client system associated

with the detected event is connected to the network using a cable modem and

wherein the step of establishing a packet filter includes the step of reconfiguring the

cable modem to selectively discard packets originating at the client system

associated with the detected event.

6. A method as recited in claim 1 wherein the step of selecting one or

more filtering rules further comprises the step of generating the filtering rules using a

standardized template.

7. A method as recited in claim 1 wherein the step of selecting one or

more filtering rules further comprises the step of selecting the filtering rules from a

database.

8. A computer program product comprising:

a computer usable medium having computer readable code embodied

therein for filtering IP packets in a computer network that includes one or

more client systems, the computer program product comprising:

first computer readable program code devices configured to

cause a computer system to detect an event associated with one of the

client systems;

second computer readable program code devices configured to

cause a computer system to provide one or more filtering rules based

on the type of event detected; and

third computer readable program code devices configured to

cause a computer system to establish a packet filter in the computer

network, the packet filter using the selected rules to selectively discard

packets originating at the client system associated with the detected

event.

9. A computer program product as recited in claim 8 wherein the detected

event is the assignment of an IP address.

10. A computer program product as recited in claim 8 wherein the detected

event is the login of a user using the client system associated with the detected

event

11. A computer program product as recited in claim 8 wherein the

computer network includes a router and wherein the third computer readable program code devices includes computer readable program code devices configured

to cause a computer system to reconfigure the router to selectively discard packets

originating at the client system associated with the detected event.

12. A computer program product as recited in claim 8 wherein the client

system associated with the detected event is connected to the network using a cable

modem and wherein the third computer readable program code devices includes

computer readable program code devices configured to cause a computer system to

reconfigure the cable modem to selectively discard packets originating at the client

system associated with the detected event.

13. A computer program product as recited in claim 8 wherein the second

computer readable program code devices includes computer readable program code

devices configured to cause a computer system to generate the filtering rules using

a standardized template.

14. A computer program product as recited in claim 8 wherein the second

computer readable program code devices includes computer readable program code

devices configured to cause a computer system to select the filtering rules from a

database.

15. An apparatus for filtering IP packets in a computer network that

includes one or more client systems, the apparatus comprising:

a first portion configured to cause a computer system to detect an

event associated with one of the client systems; a second portion configured to cause a computer system to provide

one or more filtering rules based on the type of event detected; and

a third portion configured to cause a computer system to establish a

packet filter in the computer network, the packet filter using the selected rules

to selectively discard packets originating at the client system associated with

the detected event.

16. An apparatus as recited in claim 15 wherein the detected event is the

assignment of an IP address.

17. An apparatus as recited in claim 15 wherein the detected event is the

login of a user using the client system associated with the detected event

18. An apparatus as recited in claim 15 wherein the computer network

includes a router and wherein the third portion includes a fourth portion configured to

cause a computer system to reconfigure the router to selectively discard packets

originating at the client system associated with the detected event.

19. An apparatus as recited in claim 15 wherein the client system

associated with the detected event is connected to the network using a cable

modem and wherein the third portion includes a fourth portion configured to cause a

computer system to reconfigure the cable modem to selectively discard packets

originating at the client system associated with the detected event.

20. An apparatus as recited in claim 15 wherein the second portion

includes a fourth portion configured to cause a computer system to generate the

filtering rules using a standardized template.

21. An apparatus as recited in claim 15 wherein the second portion

includes a fourth portion configured to cause a computer system to select the

filtering rules from a database.

22. An apparatus as recited in claim 15 wherein each filtering rule includes

a protocol type.

23. An apparatus as recited in claim 15 wherein each filtering rule includes

a destination address.

24. An apparatus as recited in claim 15 wherein each filtering rule includes

a destination mask.

25. An apparatus as recited in claim 15 wherein each filtering rule includes

a range of destination port numbers.