Packet Classification # 3 Ozgur Ozturk CSE 581: Internet Technology Winter 2002 Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

2 Introduction Importance Identify the context of packets  Apply necessary actions Differentiated services Memory and Time Efficiency Must handle Ks of rules Must be at wire-speed (No queuing) Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

3 Packet Classification # 3 Paper List T. Lakshman, D. Stiliadis, "High-Speed Policy-based Packet Forwarding Using Efficient Multi-dimensional Range Matching” [Bit-Parallelism] F. Baboescu, G. Varghese, "Scalable Packet Classification” [ABV: Agregated Bit Vector] M. Buddhikot, S. Suri, M. Waldvogel, "Space Decomposition Techniques for Fast Layer-4 Switching“ [Space Decomposition] V. Srinivasan, G. Varghese, S. Suri, M. Waldvogel, "Fast and Scalable Layer Four Switching“ [Paper4] Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

4 Bit-Parallelism Paper-Intro. Presents packet classification schemes traffic-independent and worst-case performance metric a few K rules, at rates of M packets per second using range matches on more than 4 packet header fields Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

5 Bit-Parallelism Paper Requirement for Real-Time Operation Traditional router architectures flow-cache architectures to classify packets identified flows are expected to arrive in near future Current backbone routers  active flows extremely high OC-3 links, 256K flows  Cashes implemented as hash tables scales well to that size Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

6 Bit-Parallelism Paper Requirement for Real-Time Operation 2 - Hash-Table Prob.s Good hash function is non-trivial 100 to 200 bits of header to be randomly distributed to no more than 20 to 24 bits of hash index header value distribution is unknown Performance of cache-based schemes is heavily traffic dependent Malicious Users limitations of hashing algo. & cashing techniques Packet queuing delays acceptable after classification Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

7 Bit-Parallelism Paper Packet Classification Constraints Scale to large routers with Gigabit links. Process at wire-speed 75% of packets < typical TCP packet size (552 bytes) Nearly half are 40 to 44 bytes (TCP Ack) Rules on several fields, specifying ranges, exact matches and prefixes Two prefix fields in some cases Allow arbitrary priorities for policies to allow distinction for multiple matches Optimize for lookups, sacrifice update performance lookup rate/update rate  Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

8 Memory access time; dominant factor in worst-case lookup execution time Amenable to hardware implementation Time vs. Space Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper Packet Classification Constraints-2

9 Decomposable search to perform multi- dimensional search for packet filtering k-dimensional query  a set of 1-dimensional queries on 1-dimensional intervals Exploit parallelism where possible Seek poly-logarithmic solution Packet header fields  k-dimensions Filters  overlapping regions in the k- dimensional space Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper General Packet Classification

10 1st Algorithm Memory: k*n 2 O(n) bits per dimension Time:  log(2n)  +1 Memory access:  n/w  2nd Algorithm Memory reduce to O(n log n) bits Time increase constant Can be optimized for time and memory budget Exploit on-chip memory in traffic-independent manner, to speed up worst case. Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper Efficiency of Proposed Algorithms

11 Notation Rule r m in k dimentions r m = (e 1,m, e2,m,…. e k,m ) e range Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

12 Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper Algorithm demo on 2-D/Preprocessing 1

13 Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper Algorithm demo on 2-D/Preprocessing 2 Max 2n+1 intervals for n rules

14 Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper Algorithm demo on 2-D/Preprocessing 3 Sets of rules formed corresponding to each region

15 P1 (x*,y*) to be classified find intervals x* and y* belongs to  binary search   log(2n+1)  +1 comparisons/dimension Create Intersection of all sets  conjunction of corresponding bit vectors Highest Priority entry in the resultant bit vector Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper Algorithm demo on 2-D/Online 1

16 Max Set Cardinality = O(n) Intersection step examines all rules at least ones  Time complexity = O(n) With bit-level parallelism The bitmaps representing sets stored in a (2n+1)*n array B j [i,1..n] (Ri,j set stored for each dimension)  k*n/w  memory accesses Different processing elements for each dimension in hardware implementation Prototype Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02 Bit-Parallelism Paper Algorithm demo on 2-D/Online 2

17 Different processing elements for each dimension in hardware implementation Prototype Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

18 Bit-Parallelism Paper- Algorithm 2 Packet Class. based on Inc. Reads Algorithm utilizes incremental reads to reduce required memory Allows time-space optimization and increases localization for off-chip SDRAM and wide on-chip memory implementations Consider a specific dimension j Assume maximum 2n+1 non-overlapping intervals Corresponding to intervals in an n-bit bitmap with the positions of the 1s indicating the filter rules that overlap this interval Adjacent intervals’ corresponding bitmaps differ in only one bit A single bitmap and 2n pointers of size log n to the differing bits can be used to reconstruct any bitmap Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

19 Bit-Parallelism Paper- Algorithm 2 Packet Class. based on Inc. Reads 2 Reduces space requirement to O(n log n) from O(n 2 ) Further Generalize (2n+1)/l bitmaps instead of 1  (2n+1)/2l  pointers needed Choose l by need  2n+1  memory reduce to O(n log n) Memory access increase  n/w  2n log n /w  Trade off decision according to on-chip/off- chip memory ratio. Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

20 Bit-Parallelism Paper- Algorithm 2 Special Case: 2-D Classification Necessary for best-effort traffic aggregation in Internet backbone Determine next hop and resource allocations based on destination and source addresses only Longest prefix match lookups  Restrict source prefix ranges to powers of 2 in order to reduce space  space requirement O(n) with trie implementation Virtual intervals  Map intervals of prefix lengths to both dimensions, sorted by length  “Virtual Intervals” allow worst-case lookup time of O(ls+log n) where ls is the number of possible prefix lengths Multicast group identification requires only two additional memory accesses Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

21 Bit-Parallelism Paper- Algorithm 2 Conclusions Packet classification, or filtering, is a useful primitive in connectionless networks to provide differentiated service and policy-based routing More recently, security and active processing Two multi-dimensional range matching algorithms allow millions of packets per second to be processed on a set of thousands of filter rules Robust and predictable worst-case performance Efficient 2-D algorithm for backbone routers with hundreds of thousands of routing entries Algorithms demonstrate that there may be no need to restrict filtering to edge routers Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

22 Paper4 Layer Four Switching Traditional router performs looking-up based on destination address Layer four switching provides increased flexibility: it gives a router the capability to distinguish and deal with traffics differently: Block traffic from dangerous site Provide QoS service for certain traffics Give preferential treatment to certain traffic (say, database flow). Difficulties: need layer four header information, which may not always available any modification of layer four header may cause problems Do not how to get header info when encrypted Some variants of L4S: Firewall Reservation protocols such as RSVP Routing based on traffic type, say web traffic

23 A packet P has k distinct header fields for lookup: H[1], …, H[k] The filter database of a Layer 4 Router consists of a finite set of filters: F 1, F 2, …, F N, each filter F i has an associated directive act i Match: each field of P matches the corresponding field of F Cost: used to determine an unambiguous match (say order of filters) An address range can always be transferred into a sequence of prefixes so we can use prefix match Paper4 The Best Matching Filter Problem Dest M T1 * Net * Src * S * T0 Net * DP * SP * 123 * SP * UDP * UDP * TCP-ACK * A filter database A packet example: (M, S, UDP, 53, 125)

24 Paper4 Set Pruning Trees (1) Build a trie on the destination prefixes in the database Each valid prefix in the destination trie points to a trie containing some source prefixes. A single filter may be fit into multiple destination prefixes, thus has multiple source trie copies. Memory space: O(N 2 ) Time complexity: O(N)

25 Set Pruning Trees (2) Dest-Trie Src-Trie F1 F7F2F5F7F2F7 F6 F3 F4 E.g.: Looking for: (001, 001)

26 Avoid the Memory Blowup (1) Avoid the copying by having each destination prefix D point to a source trie that stores the filters whose destination field is exactly D When searching, may need go back to the destination trie for multiple times Time complexity: O(W 2 ) Space complexity: O(NW)

27 Avoid the Memory Blowup (2) Dest-Trie Src-Trie F1F5F2F7 F6 F3 F4 E.g.: Looking for: (001, 001) Memory requirement=O(NW) Lookup Worst Case= O(W 2 )

28 Improving Search Time: Basic Grid-of-Tries (1) Basic idea: Use pre-computation and switch pointers (in the lower lever tries) to speed up search in a later source trie base on the search in an earlier source trie. (Remember the previous searching result) Role of switch pointer Allow us to increase the length of the matching source prefix, without having to restart at the root of the next ancestor source trie. Stored Filter: node (D,S) stores the least cost filter whose dest field is a prefix of D and src field is a prefix of S Time complexity: 2W Space complexity: O(NW)

29 Improving Search Time: Basic Grid-of-Tries (2) Dest-Trie Src-Trie F1F5F2F7 F6 F3 F x y E.g.: Looking for: (001, 001)

30 Further Improvement & Extension Use some faster scheme for destination address matching Time complexity O(W)  O(log W) Use multi-bit tries for source address matching Time complexity O(W)  O(W/k) Extend Grid-of-tries to handle protocol and port fields 3 GOT copies for TCP, UDP and OTHER respectively, 4 hash tables for 4 port combinations:  both unspecified, destination only, source only, both specified

31 How-to Slice filter database into column, the i-th column storing all distinct prefixes in field i. Make a cross-product table of all k columns Pre-compute the least cost filter that matches each cross-product entry When packet comes in, do best prefix matching for each field respectively With matching results, find out the corresponding entry in the cross-product table Discussion Very fast (for matching) Problem: memory explosion: N^k Solution: On Demand Cross-Producting Cross-Producting (1)

32 Cross-Producting (2) Dest Prefix Src Prefix DestPort Prefix SrcPort Prefix Flags Prefixes M T1 Net Default S T0 Net Default Default 123 Default UDP TCP- ACK Default NumCrossProductMatching Filter … M, S, 25, 123, UDP M, S, 25, 123, TCP-ACK M, S, 25, 123, default M, S, 25, default, UDP M, S, 25, default, TCP-ACK M, S, 25, default, default … default,default,default,default,TCP-ACK default,default,default,default,default F1 … F8 E.g. Looking for: (M,S,UDP,25,57) Dest M T1 * Net * Src * S * T0 Net * DP * SP * 123 * SP * UDP * UDP * TCP-ACK *

33 Conclusions GOT solution scalable (linear) storage & fast lookups for D-S filters. More general filters  high lookup cost Cross-Producting solution, higher variance, but faster on average (for lookup) because of cashing need. Hybrid scheme combines flexibility with efficiency. Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

34 ABV: "Scalable Packet Classification” F. Baboescu, G. Varghese, GOAL Packet classification  scalable (in rules, upto 100,000)  wire speed Past Work Linear time search Linear amount of TCAMS Lucent scheme  worst case doesn't scale Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

35 SOLUTION Aggregated Bit Vector improvement on Lucent bit vector rule aggregation rule rearrangement Rule Aggregation bit vectors are sparse  i.e., few rules match Some compression scheme Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

36 SOLUTION continued Rule Rearrangement overlap is rare place rules w/ common values together sort out rule ordering later Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

37 Comparing ABV w/ BV of Lucent Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

38 Results At least an order magnitude faster than BV Scales well for memory access Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

39 Paper # 3 “Space Decomposition Techniques for Fast Layer-4 Switching" M. Buddhikot, S. Suri, M. Waldvogel new scheme, based on space decomposition, whose search time is comparable to the best existing schemes, but which also offers fast worst-case filter update time. three key ideas innovative data-structure based on quadtrees for a hierarchical representation of the recursively decomposed search space fractional cascading and precomputation to improve packet classification time prefix partitioning to improve update time Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02

40 Space Decomposition Evaluation Depending on the actual requirements of the system this algorithm is deployed in, a single parameter  can be used to tradeoff search time for update time. Amenable to fast software and hardware implementation. For N two-dimensional filters specified using prefixes of up to W bits in length, Area-based Quadtrees (AQT) data structure requires O(N) space, O(  W) search time, and O(  (N) 1/  ) Both the average and worst-case search times and memory consumption are comparable or better than other schemes known in the literature. Packet Classification # 3CSE 581: Internet Technology (Winter 2002)Ozgur Ozturk02/11/02