FIELD OF THE INVENTION

The invention relates to the field of data networking. In particular, the invention relates to technologies for packet and flow identification in networks.

DESCRIPTION OF THE RELATED ART

Longest match searches are a ubiquitous feature in data networking technology, particularly for packet routing. For instance, in IP routing, a destination address for a given packet is matched against a routing table; amongst the multiple entries that match the destination address, the router picks the entry which has the longest subnet mask.

Given the prevalence of the longest prefix matching techniques, routing and packet processing hardware are typically implemented to support such algorithms. However, it may be desirable to match packets against additional parameters in a table by use of techniques other than longest match. For instance, network firewalls typically identify and filter packets based on numerous parameters in the packet headers. Moreover, rules that are implemented by firewalls for packet filtering are typically inserted through an interface such as a Command Line Interface, or CLI. Rules are typically presented to such interfaces in priority order, wherein the order of priority—rather than the length of a pattern match—dictates which rule is matched to the packet.

It may be desirable to accelerate packet processing devices such as a network firewall by use of hardware which implement longest match searches; however, such a device should be able to accept rules which are presented in priority order. As such, there is a need for technology to convert priority-based rules into equivalent rules suitable for a longest match search.

Another difficulty with prior art packet processing technologies is the rigidity and inflexibility, which precludes the use of such technology for general purpose packet matching. Fast packet processing is typically achieved by the use of dedicated hardware. Some routers, for instance, include customized ASICs for packet processing; as these ASICs are dedicated to specific networking tasks, they cannot be reprogrammed to search for different types of patterns in packets. Recent years have witnessed the introduction of programmable network processors. These network processors are limited in their programmability, however, as their data structures are generally fixed in size and are dedicated to specific types of searches on packets, such as longest matches on specific networking parameters. As such, there is a need to implement new types of data structures in network processors which allow searches on arbitrarily many networking parameters of different lengths.

SUMMARY OF THE INVENTION

The invention includes systems and methods for converting priority based rules into isomorphic longest match rules. In some embodiments of the invention, rules for packet processing are presented to a networking device in priority order. These rules may be presented to the networking device through an interface such as a Command Line Interface, or CLI. Alternatively, the rules may be presented by one or more software applications; these software applications may, in some embodiments, reside at least partially on the networking device itself.

In some embodiments of the invention, the networking device includes a hardware and/or software layer, referred to as a forwarding layer, for accelerating packet processing; the forwarding layer includes hardware and/or software designed to perform longest match searches on packets. The prioritized rules are converted into a data structure for the forwarding layer, which may include one or more longest match trees; this transformation ensures that for any given packet entering the networking device, a longest match search performed by the forwarding layer on the data structure is equivalent to a priority order search on the prioritized rules.

These and other embodiments are described in greater detail infra.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1

schematically illustrates a forwarding layer of a networking device according to embodiments of the invention.

FIG. 2

illustrates a Command Line Interface used by embodiments of the invention.

FIG. 3

illustrates a data structure for matching packets to arbitrary rules according to an embodiment of the invention.

DETAILED DESCRIPTION

The embodiments and examples described herein are intended for illustrative purposes only; alternative embodiments shall be apparent to those skilled in the art.

A. Networking Environment

A networking environment relevant to the invention is illustrated schematically in FIG.

1

. The environment includes a Networking Device

100

which includes one or more external interfaces

102

for transmitting data. The Networking Device

100

includes a forwarding layer

104

for inspecting packets traversing the Networking Device via the external interfaces

102

. The forwarding layer may incorporate one or more ASICs, Network Processors including firmware, or general purpose CPUs with specified packet-forwarding software. In embodiments incorporating Network Processors, examples of suitable Network Processors include the Intel® IXP Chip, the Agere family of Network Processors, or Motorola Inc.'s C-Port network processor; other suitable network processors will be apparent to those skilled in the art. Network processors available as of the time of this writing may operate at rates of OC-48, OC-192, or OC-768. In a non-limiting embodiment, the Networking Device

100

may be a programmable networking device, as described in U.S. applications Ser. No. 09/679,321, filed Oct. 3, 2000, inventors Junaid Islam, Hoamyoun Valizadeh, and Jeffery S. Payne, and U.S. Pat. No. 09/918,363, filed Jul. 30, 2001, inventors Junaid Islam, Hoamyoun Valizadeh, and Jeffery S. Payne, which are hereby incorporated by reference in their entirety.

The Networking Device also includes a user space environment

106

enabling system administrators to control and interact with the device

100

. The user space environment

106

typically includes a Command Line Interface, or CLI, and may communicate with the networking device

100

via a management port

108

. The CLI includes instructions allowing the user to specify instructions to the forwarding layer

104

for packet handling.

FIG. 2

illustrates a typical set of commands entered into Command Line Interface for a Networking Device. In this example, a series of prioritized rules

200

are presented to the networking device

100

via the CLI; these rules are presented in order of priority, such that when a packet arrives at the Networking Device from an external interface, the headers of the packet are matched against the rules in the order of priority. When a rule is found that matches the packet, actions specified in the rule are taken for that packet. In a non-limiting embodiment, the rules may be presented in descending order of priority

218

. Alternatively, the rules may be presented in increasing order of priority; other arrangements for prioritizing rules shall be apparent to those skilled in the art.

B. Longest Match Trees

In embodiments of the invention, the forwarding layer

104

may search for matches in the packet headers by use of a longest match search on a Longest Match Tree; longest match searches are well known in the art. A non-limiting example of Longest Match Tree

300

is illustrated in FIG.

3

. The Longest Match Tree may include subtrees, or filters

302

304

306

308

, which may have different widths; in the illustrated embodiment

300

, the subtrees

302

304

306

308

are of four different widths. When a packet arrives at the forwarding layer

104

, the headers are retrieved from the packet and are matched against the Longest Match Tree

300

by use of a longest match search.

In embodiments of the invention, each filter Filter

0

300

Filter

1

302

Filter

2

304

Filter

3

306

may handle fields of a different size. As an illustrative, non-limiting example, suppose the forwarding layer

104

processes TCP/IP packets, and that Filter

0

300

has a width of 0-1 bytes. Then those fields in TCP/IP which have a width of 0-1 bytes may be searched within it. For instance, these fields in the IP Header may include Type of Service (TOS), 8-bit Protocol, 8-bit time to live (TTL). Filter

1

302

may have a width of 1-2 bytes, sufficient for fields such as IP Source Port and Destination Port. Filter

2

304

has a width of 2-3 bytes. Filter

3

306

, which has a width of 3-4 bytes, can accommodate fields such as TCP Source IP Address and Destination IP Address.

C. Conversion of Prioritized Rules for Longest Match Searches

1. Form of Prioritized Rules

Embodiments of the invention include mechanisms for converting prioritized rules

202

presented in a Rule Database

200

as illustrated in

FIG. 2

200

into an equivalent rules suitable for a longest match search; in some embodiments of the invention, the equivalent rules are used to populate a longest match tree

300

, which is then searched by the forwarding layer

104

. Each rule

202

in the Rule Database

200

includes one or more values

204

206

208

for one or more corresponding fields

212

214

216

. In embodiments of the invention, the fields

212

214

216

may correspond to various parameters in TCP and IP headers, and the values

204

206

208

may be possible values of these TCP/IP parameters. As an example, the fields

212

214

216

may correspond, respectively, to the TCP/IP parameters of ‘Source Address,’ ‘Destination Address,’ and ‘Port Number, ’while the respective values

204

206

208

may be any arbitrary values addresses or port numbers, such as, respectively, ‘180.33.22.11’, ‘20.10.80.68’, ‘8080’.

In some embodiments of the invention, a value in a field may include a bit mask: for instance, a field

212

may be Source IP Address, and a value

204

for the Source IP address in a rule may be 180.55.x.x, wherein the x.x is a bit mask, indicating that the value matches to any packet with a Source IP Address containing 180.55 in its first 64 bits.

Given any two values in a field where a first value is a proper subset of the second value (or equivalently, the second value is a proper superset of the first value) a longest match search on the field will return the subset. To illustrate, suppose we perform a longest match search on the field Source IP Address

212

, which contains the values 180.55.x.x

204

and 180.55.33.22 218, corresponding, respectively, to rule 1 and rule 2. As discussed above, 180.55.33.22 is a special case of 180.55.x.x; thus, the value 180.55.33.22 is a subset of the superset 180.55.x.x, and a longest match search for the address will accordingly return rule 2.

2. Use of Virtual Trees for Longest Match Searches

Embodiments of the invention supplement the Longest Match Tree

300

with Virtual Trees; each of the filters

300

302

304

306

may include one or more Virtual Trees, and each Virtual Tree may be identified by a distinct Virtual Tree Number. In some embodiments of the invention, each Virtual Tree corresponds to a distinct field

212

214216

in the Rules Database

200

, and contains multiple possible values

204

206

208

for the field; the virtual tree then acts as a C-style case statement.

To illustrate the deployment of Virtual Trees in the Longest Match Tree

300

, consider the following non-limiting example. Suppose the forwarding layer

104

handles TCP/IP packets. Virtual trees

310

312

314

316

in Filter

0

302

may handle fields of 0-1 bytes, such as, for example TOS or Protocol fields; thus each of the virtual trees

310

312

314

316

in Filter

0

corresponds to either TOS or IP Protocol, and stores one or more values for the respective field. Filter

1

304

may handle field of 1-2 bytes in length, such as Source Port or Destination Port; in the example, Filter

1

304

includes virtual trees

318

-

336

, each of which corresponds to Source Port or Destination Port, and includes one or more values for the corresponding field; Filter

2

306

supports virtual trees for fields of width 2-3 bytes; in this example, no such fields are searched. Filter

3

308

may handle virtual trees for fields of length 3-4 bytes, such as Source IP Address and Destination IP Address; in the example, Filter

3

306

includes virtual trees containing values for either the Source IP Address or the Destination IP Address.

When a packet arrives at the forwarding layer

104

, a longest match search of the headers of the packet is performed against the Longest Match Tree (LMT)

300

. If a value in the LMT is matched, then a corresponding action is taken. To elaborate, each entry in each virtual tree in the LMT

300

includes a value and a corresponding action. The action may be to search another parameter in the packet header. Alternatively, the action may be a particular type of operation on the packet; such an operation may, by way of non-limiting example, may be to forward the packet according to instructions, or to transform or alter the packet according to specified instructions.

3. Populating the Virtual Trees

Embodiments of the invention include algorithms to convert the prioritized rules in the Rules Database

200

to populate Virtual Trees in the Longest Match Tree

300

. This ensures that for any given packet entering the forwarding layer

104

, longest match searches on the Longest Match Tree

300

produce isomorphic results to a search through the prioritized Rules Database.

In some embodiments of the invention, the Rules Database

200

may be converted to a set of rules which are isomorphic under a longest match search. By way of non-limiting example, the algorithm presented in pseudo-code below may be used by some embodiments of the invention to perform this transformation:

Find first field/column;

choose unique VTN;

record first field and VTN

buld_graph(VTN=0, DB = all_rules, next_column);

buld_graph(VTN, DB, next_column) {

For each value/row in the column {

If there is a lower priority rule such that the

current value is a superset of the corresponding

value for the lower priority rule, then

Insert a new rule, immediately above the

current rule in priority, such that the new

rule includes the corresponding value (i.e.,

the subset)as the value for the current

field--the remainder of the rule remains

identical

If there is a higher priority rule such that the

current value is asuperset of the corresponding

value for the higher priority rule, then

Insert a new rule, immediately above the

current rule in priority, such that the new

rule includes the corresponding value (i.e.,

the subset)as the value for the current

field--the remainder of the rule remains

identical

}

remove redundant rules;

for each distinct value_0 of the column {

new DB = subset of DB where value = value_0;

remove the column from new_DB;

Find next field/column;

if next_field != NULL, {

store field offset, VTN and size of the

field

build_graph(new_DB, news_VTN, next_column);

}

else

store action;

}

By employing the algorithm described above—or equivalents or variants thereof—to populate the data structure

300

, the longest match search performed on the LMT

300

will be isomorphic to the priority-ordered rules used to generate the LMT

300

. Note that the algorithm presented above is for illustrative purposes only; many equivalents and variants shall be apparent to those skilled in the art.

D. Illustration of Rule Conversion Techniques

The techniques for converting prioritized rules into Longest Match Trees are illustrated herein by use of examples. By way of non-limiting example, suppose we have the following rules presented to the networking device via in descending order of priority:

Rule #

Source IP

Dest IP

Port #

Action

1

180.55.x.x

1.1.1.1

x

A

2

180.55.44.33

1.1.x.x

x

B

3

180.55.x.x

x.x.x.x

80

C

4

x.x.x.x

x.x.x.x

x

D

The operation of the algorithm described above upon the prioritized rules produces the following results:

vtn = 0, field = Src IP, LMT = 0:

Src IP

Dest IP

Port

Act

Ptr

180.55.44.33

1.1.1.1

x

A

vtn = 1, field = IP Dest, LMT = 0

180.55.x.x

1.1.1.1

x

A

vtn = 2, field = IP Dest, LMT = 0

180.55.44.33

1.1.x.x

x

B

vtn = 1, field = IP Dest, LMT = 0

180.55.44.33

x.x.x.x

80

C

vtn = 1, field = IP Dest, LMT = 0

180.55.x.x

x.x.x.x

80

C

vtn = 2, field = IP Dest, LMT = 0

180.55.44.33

x.x.x.x

x

D

vtn = 1, field = IP Dest, LMT = 0

180.55.x.x

x.x.x.x

x

D

vtn = 2, field = IP Dest, LMT = 0

x.x.x.x

x.x.x.x

x

D

vtn = 3, field = IP Dest, LMT = 0

Dest IP

Port

Act

Ptr

vtn = 1, field = IP Dest, LMT = 0:

1.1.1.1

x

A

ACTION A

1.1.1.1

x

B

ACTION A

1.1.x.x

x

B

ACTION B

1.1.x.x

80

C

ACTION B

1.1.1.1

80

C

ACTION A

x.x.x.x

80

C

1.1.x.x

x

D

ACTION B

1.1.1.1

x

D

ACTION A

x.x.x.x

x

D

vtn = 0, field = PORT, LMT = 1

vtn = 2, field = IP Dest, LMT = 0:

1.1.1.1

x

A

ACTION A

1.1.1.1

80

C

ACTION A

x.x.x.x

80

C

vtn = 1, field = PORT, LMT = 1

1.1.1.1

x

D

ACTION A

x.x.x.x

x

D

vtn = 1, field = PORT, LMT = 1

vtn = 3, field IP Dest, LMT = 0:

x.x.x.x

x

D

ACTION D

Port

Act

Ptr

vtn = 0, field = PORT, LMT = 1:

80

C

ACTION C

80

D

ACTION D

x.x.x.x

D

ACTION D

vtn = 1, field = PORT, LMT = 1:

80

C

ACTION C

80

D

ACTION C

x.x.x.x

D

ACTION D

E. Alternative Embodiments

In some embodiments, the Rules Database

200

may be accessed and manipulated by applications residing on the programmable network device, or solfware applications which may be outside the device. These rules may be manipulated and downloaded to the forwarding layer in real-time.

The embodiments described above are for illustrative purposes only. Many equivalents and variants will be apparent to those skilled in the art.