An Efficient Hardware-based Multi-hash Scheme for High Speed IP Lookup Department of Computer Science and Information Engineering National Cheng Kung University,

An Efficient Hardware-based Multi-hash Scheme for High Speed IP Lookup

Department of Computer Science and Information Engineering National Cheng Kung University, Taiwan R.O.C.

Authors: Socrates Demetriades, Michel Hanna, Sangyeun Cho and Rami MelhemPublisher: High Performance Interconnects, 2008. HOTI '08. 16th IEEE Symposium on 26-28 Aug. 2008Present: Chia-Ming ,Chuang Date: 9, 24, 2008

Outline

1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion

Introduction (1/3)

Ternary Content Addressable Memory (TCAM)

Trie-based schemes Hash-based schemes

Current techniques IP lookup have three categories

Introduction (2/3)

First hashing can happen collisions and requires resolution

techniques that may result in unpredictable lookup performance

Second hash keys be included “don’t care” bit

Three determine the longest prefix

hash-based IP lookup problem

Introduction (3/3)

High lookup throughput

• A multiple table , multiple hash functions

• Bit select mechanism high space utilization

• Modified version of the Cuckoo hashing algorithm Low power consumption

• Sum of advantage

Outline

1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion

Architecture overview (1/4)

Architecture (2/4)

Based on a multi-level hash table (MHT)

All hash function use the same bit position in a prefix or a

destination address

PS:references [16] S. Cho, J. Martin, R. Xu, M. Hammoud, and R. Melhem, “Ca-ram:A high-performance memory substrate for search-intensive applications,”pp. 230–241, IEEE ISPASS, April 2007.

Architecture (3/4)

Architecture (4/4)

Do not classify prefixes based on their lengths Each table is accessed using a hardware based

index generator a number of match processors compare the fetched

keys with the search key in parallel

“Bit-Select” component (1)decides which bits participate in the index generation

(2)“don’t care bits” may appear in the selected bits for indexing

(3)Bit-Select mechanism needs to resolve this by prefix expansion

Outline

1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion

Bit select mechanism (1/7)

Bit select mechanism (2/7)

(一 ) Most prefix have lenghts between16 and

24 bits 24 bit prefixes comprise about 54% no prefixes less than 8 bit (二 ) As a study in [9] pointed out, regardless

of prefix length, start from the6th bit and reach the prefixes’ maximum length.

Bit select mechanism (3/7)

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Bit select mechanism (4/7)(一 ) X-axis =>(Expansion size)/extra provided capacity Y-axis=> unresolved collisions no prefixes less than 8 bit(二 ) From the experiments, we find that any c

onfiguration that can keep the expansion between 20% and 90% of the extra provided capacity results in less than 5% of unresolved collisions.

Bit select mechanism (5/7)

controlled prefix expansion

controlled wildcard resolution

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Max bucket is 234 itemMax bucket is 49 item

Total 49*3=147Cuckoo hashing algorithm

Bit select mechanism (6/7)

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Bit select mechanism (7/7)(一 ) a collision may appear if an item x can not be inser

ted into tables Ti, i = 1, . . . , d because buckets Ti [hi(x)], i = 1, . . . , d are full.

(二 ) by checking whether an item y at some bucket Ti [hi(x)], 1 ≤ i ≤ d, can migrate to some other table Tj =\ Ti. This requires that a bucket Tj [hj(y)] has an

empty entry to accommodate the item y.(三 ) If such an item y is found, then it can be moved a

nd x will take its place.

Outline

1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion

Conclusion (1/3)

Conclusion (2/3)

Conclusion (3/3)