Packet Classification on Multiple Fields

참고 논문 : Pankaj Gupta and Nick McKeownSigComm 1999

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IP Lookup

Longest-prefix address lookup

Rule: Each Prefix

Action: Next hop Classifier: Forwarding table

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Outline

Packet Classification Application, Information,

Characteristics

Design GoalPrevious WorkRecursive Flow Classification (RFC)

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Packet classification(Application)

Packet Filtering Deny all traffic from ISP3

destined to E2

Accounting & Billing Treat all video traffic to

E1 as highest priority and perform accounting for the traffic sent this way

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Packet classification(Application)

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Packet Header

http://vulcan.ee.iastate.edu/~dougj/class/580/index.htm

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Example

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Example (Cont.)

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Definition of Packet Classification

Each rule Specifies a class Based on criterion on F fields Associates with an identifier, classID i-th component of the rule R, R[i]

A regular expression on the i-th filed of the packet header

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Characteristics of P-C

793 packet classifiers 101 different ISP and enterprise networksTotal 41505 rules? Data representative? Conclusion: Trivial or non-trivial?

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Distribution of total number of rules per classifier

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Characteristics 1

The classifiers do not contain a large number of rules. 0.7% of the classifiers contain more

than 1000 rules Mean number: 50 rules

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Characteristics 2

The syntax allows a maximum of 8 fields to be specified: Source/destination Network-Layer

address(32-bits) Source/destination Transport-layer

port number(16-bits for TCP/UDP) Type-of-service field(8-bits) Protocol field (8-bits) Transport-Layer protocol flags(8-bits)

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Characteristics 3-4

Transport-Layer protocol field is restricted to a small set of values: TCP, UDP, ICMP, IGMP, (E)IGRP, GRE

and IPINIP or wildcard

Transport-layer fields Many (10.2%) are range

specifications

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Characteristics 5-6

14% of all the classifiers had a rule with a non-contiguous mask.Many different rules share a number of field specifications.

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Characteristics 7

Redundant Backward redundancy

Rule T appears earlier than Rule R, and R is a subset of T.

Forward redundancy Rule T apperas after R

R is a subset of T R, T have the same action Rules inbetween R and T

The same action Disjoint from R.

8% of the rules were redundant.

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Goals

Fast enough Matching on arbitrary fieldsSupport general classification rules Prefixes, operators(like range, less than,

greater than…) and wildcards.

Suitable for software and hardware implementationMemory efficientScalabilityFor steady classifier

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Previous Work

Sequential evaluationsGrid of TriesCrossproductingBit-level parallelismTCAM

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Abstract

The point location problem in multidimensional spaceFind the enclosing region of a point, given a set of regions.Complexity O(logn) in time with O(nF) space O(logF-1n) time with O(n) space

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Structure of classifiers

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Overlapping is small

For the biggest classifier with 1734 rules, the number of distinct overlapping regions in four dimensions to be 4316, compared to a worst possible case of approximately 1013.

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Recursive Flow Classification

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Chunks of Packet header

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Packet flow in RFC

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Phase number =3

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Phase number =4

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Select Phase number

Combine those chunks together which have the most “correlation”.Combine as many chunks as possible without causing unreasonable memory consumption.Best case: P=3 Tree B P=4 Tree A

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Performance (Storage requirement for

P=2)

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Performance (Storage requirement for P=3)

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Performance (Storage requirement for P=4)

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Preprocess Time

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Hardware implementation

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Larger classifiers IConcatenating the classifiers belonging to the

same network.

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Larger classifiers II

Concatenate all the classifiers of a few (up to ten) different networks. RFC frequently runs into storage

problems for classifiers with more than 6000 rules.

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Variations

Process a larger number of fields in each packet header.Use available fast lookup algorithmsUse Adjacency group

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Adjacency Groups

Two rules (R, S)are considered adjacent R appears first The same Action All but one field have the same

specification All rules in between R and S

Either have the same action Disjoint from R

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An example

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Storage (Adjacency groups)

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Comments

Trade off? Memory, Speed, Dynamic Change, etc

Application and Demand orientedFurther discussion? scai@ecs.umass.edu

Thank you!