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AN ON-CHIP IP ADDRESS LOOKUP ALGORITHM

This paper presents a hardware design reference model for an on-chip IP address lookup algorithm, proposing a scheme with compressed endpoints and shared pointers to build the tree, resulting in improved performance. Published in IEEE Transactions on Computers, 2005.

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AN ON-CHIP IP ADDRESS LOOKUP ALGORITHM

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  1. AN ON-CHIP IP ADDRESS LOOKUP ALGORITHM Author: Xuehong Sun and Yiqiang Q. Zhao Publisher/Conf.: IEEE TRANSACTIONS ON COMPUTERS,2005 Speaker: Han-Jhen Guo Date: 2008.11.19

  2. OUTLINE • Hardware Design Reference Model • Convert Longest Prefix Match To Range Search Problem • Proposed Scheme • Compressed Endpoints • Shared Pointers • Build The Tree (Bottom Up) • Performance

  3. HARDWARE DESIGN REFERENCE MODEL chip (internal) mem. acess time = 1.25ns (several times faster than DRAM) external 13 bits Next Hop Information des. IP address

  4. CONVERT LONGEST PREFIX MATCH TO RANGE SEARCH PROBLEM (1/4) • Definition • [b, e) is defined as the range of the prefix P • b and e are defined as the left endpoint and right endpoint of prefix P

  5. CONVERT LONGEST PREFIX MATCH TO RANGE SEARCH PROBLEM (2/4) Routing table (len. = 6) Range representation

  6. CONVERT LONGEST PREFIX MATCH TO RANGE SEARCH PROBLEM (3/4) • Port merging C A B A C C D C A C A A C A B A C D C A C A

  7. CONVERT LONGEST PREFIX MATCH TO RANGE SEARCH PROBLEM (4/4) • The IP address lookup problem is converted into the predecessor finding problem in a priority queue • given a set of sorted integers S and an integer i, find an integer e in S such that e is the biggest one which is less than or equal to i search 39

  8. PROPOSED SCHEME- COMPRESSED ENDPOINTS (1/4) • eg. real-life IPv4 endpoints trailing zeros common leading bits (CLB) keys

  9. PROPOSED SCHEME- COMPRESSED ENDPOINTS (2/4) • Data structure of one word in on-chip memory (row data structure of a node of the tree) 1 4 5 5 144 - (1 + 4 + 5 + 5 + 20) = 109 20 inter. node: index of next lv. node leaf node: index of port info.

  10. PROPOSED SCHEME- COMPRESSED ENDPOINTS (3/4) • Set up the field of common leading bits • to calculate the number of common leading bits of the smallest and the biggest endpoints in the group • O(2) • Set up the field of trailing zeros • the first endpoint are counted and recorded as the candidate number of common trailing zeros • the trailing zeros of the next endpoint are counted • if the number of the trailing zeros of the next endpoint is smaller than the candidate number, the candidate number is changed to the smaller one • otherwise the candidate number is unchanged • O(N), N is # of nodes in a group

  11. PROPOSED SCHEME- COMPRESSED ENDPOINTS (4/4) • eg. real-life IPv4 endpoints trailing zeros common leading bits (CLB) keys

  12. PROPOSED SCHEME- SHARED POINTERS • eg.(apply to B-tree) 0 1 2 3 4

  13. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) • Given a set of sorted endpoints, we assign endpoints to leaf nodes and then to the next highest level until the root level • Select the first four endpoints as a group and calculate tb (= the total bits of the compressed keys) • tb = 109 → store these four endpoints a word (group) • tb > 109 → store first three endpoints a word • tb < 109 → check if can store (4 + 1) endpoints...

  14. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) a • Variant 1 • grouping • a~d: 13*4=52 < 109 • a~e: 14*5=70 < 109 • … • a~g: 14*7=98 < 109 • a~h: 14*8=112 > 109 → {a,b,c,…,g} is a leaf, then h should be higher lv. • i~j: … b c d e f g h i j k L m

  15. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) a • Variant 1 • after grouping b c d e f g h i j k L m

  16. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) a • Variant 1 • eg. mistaking CLB b c d 10011111 F F 00 e f g h 10011111 F F 0 i j k L 1111 F F (EORROR!) m

  17. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) a • Variant 1 • compute CLB and trailing 0s b c d e f 5 g h h i 1 j k L m

  18. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) a • Variant 1 • searching b c d 10011111 F F 00 e f g h 10011111 F F 0 i 0011111 F F j k L m

  19. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) a • Variant 2 • grouping • a~d: 13*4=52 < 109 • a~e: 14*5=70 < 109 • … • a~g: 14*7=98 < 109 • a~h: 14*8=112 > 109 → {a,b,c,…,g} is a leaf • h~k: … b c d e f g h i j k L m

  20. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) a • Variant 2 • after grouping b c d e f g h i j k L m

  21. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) n1 a • Variant 2 • creating new endpoints to next higher lv. b c d e f g n2 CLB(n1, n2) h i j k CLB(n2, n3) n3 L m CLB(n3, m)

  22. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) n1 a • Variant 2 • searching b c d 10011111 F 1111 e f g n2 h 10011111 F F 0 i 10011111 F 1111 j k n3 L m

  23. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) • Variant 3 • apply variant 1 to lower levels apply variant 2 to higher levels • in experiment of perfomance • variant 1 are applied to leaflevels variant 2 are applied to other higherlevels

  24. PROPOSED SCHEME- BUILD THE TREE (BOTTOM UP) • Variant 4 • divides the endpoints into groups according to their leading bits • according to groups, respective tree structure is created using techniques described in this paper (variant 1 or 2)

  25. PERFORMANCE • Port merge effect (IPv4)

  26. PERFORMANCE • Comparisons on variants (width = 144) (IPv4) • variant 3 is well balanced min mem. req. max mem. access time min mem. access time max mem. req.

  27. PERFORMANCE • Implement with variant 3 • ME ratio = mem. req. in bits / # of prefixes • Arityof a node = the # of subtrees of the node • memory access times = logArity (table_size) Results of IPv6 Using 168 Bits Memory Width Results of IPv4 Using 144 Bits Memory Width probably due to a high percentage (above 70 percent) of length 48 prefixes

  28. PERFORMANCE • Memory size for IPv4 as a function of table size with different memory widths better choices

  29. PERFORMANCE • Memory size for IPv6 as a function of table size with different memory widths better choices

  30. PERFORMANCE • Number of Memory Accesses for IPv4 and IPv6 as a Function of Table Size and Memory Width IPv4 both are NOT sensitive to table size IPv6

  31. Thanks for your listening!

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