An Efficient IP Lookup Architecture with Fast Update Using Single-Match TCAMs

1. An Efficient IP Lookup Architecture with Fast Update Using Single-Match TCAMs Author: Jinsoo Kim, Junghwan Kim Publisher: WWIC 2008 Presenter: Chen-Yu Chaug Date: 2008/11/12

2. Outline • Introduction • Related work • Propose IP Lookup Architecture • IP Lookup and Update Algorithms • Performance Evaluation • Conclusion

3. Introduction(1/4) • Most of the IP lookup schemes can be classified into software approaches based on trie and hardware approaches based on TCAM (Ternary Content Addressable Memory). • Trie-based IP lookup schemes usually require several memory accesses. In contrast, TCAM can perform a lookup operation in a single cycle owing to its parallel access characteristics. Therefore, TCAM have been paid much attention to in recent years.

4. Introduction(2/4) • There may be several matches in an IP lookup operation, it is required to determine the best match, i.e., LMP. • For the determination of the LMP, all prefixes of a TCAM needs to be ordered by some criteria such as length. Under the ordered circumstance a priority encoder can select the LMP on the uppermost location among all matched prefixes.

5. Introduction(3/4) • Most of TCAM-based lookup schemes need several movements of prefix entries for a single update because the ordering must be maintained in the TCAMs. • Therefore, frequent updates may consume many computation cycles in the IP lookup engine and result in the degradation of the lookup performance.

6. Introduction(4/4) • In this paper, we present a new architecture to provide fast update by using single-match TCAMs. • Our algorithms guarantee that each single-match TCAM generates at most one match for a given destination address. So, it can eliminate both the ordering constraint and the priority encoder in a single-match TCAM, which makes the update fast.

7. Outline • Introduction • Related work • Propose IP Lookup Architecture • IP Lookup and Update Algorithms • Performance Evaluation • Conclusion

8. Ordering constraint • Prefix-length ordering constraint: Two prefixes of the same length don’t need to be in any specific order. • L-algorithm • PLO_OPT • Chain-ancestor ordering constraint There’s an ordering constraint between two prefixes if and only if one is a prefix of the other. • CAO_OPT

9. L-algorithm • Two prefix in the same length can be in any order. • L-algorithm, that can create an empty space in a TCAM in no more than L memory shifts (recall that L = 32 ).

10. PLO_OPT • The basic idea of the PLO_OPT algorithm is to keep all the unused entries in the center of the TCAM. • PLO_OPT brings down the worst-case number of memory operations per update to L/2.

11. Better Algorithm ? P4 31 Maximal chain P2 has no ordering constraint with P3 or P4. P3 29 P2 15 PLO constraint is too Restrictive than needed. 8 P1

12. CAO_OPT(1/2) • The CAO_OPT algorithm also keeps thefree space pool in the center of the TCAM. • Basic idea: for every prefix, the longest chain that this prefix belongs to should be split around the free space pool as equally as possible.

13. P4 P2 P3 P1 CAO_OPT(2/2) P4 < P3 < P1, P2 < P1

14. Summary of Simulation Results

15. Outline • Introduction • Related work • Propose IP Lookup Architecture • IP Lookup and Update Algorithms • Performance Evaluation • Conclusion

16. Location Prefix Next-hop 1 0 P1 103.23.122/23 171.3.2.22 1 P2 103.23/16 171.3.2.4 1 0 P3 101.1/16 120.33.32.98 2 Priority Encoder 103.23.122.7 P1 0 P4 101.20/13 320.3.3.1 3 0 P5 100/9 10.0.0.111 4 0 5 0 6 Conventional TCAM-Based Architecture • Conventional TCAM-based IP Lookup architecture in PLO (prefix length order).

17. Design of the Proposed Architecture(1/4) • The maximum number of matched entries in a TCAM depends on the maximum depth of levels of the prefix search trie. • The maximum length of any chain currently does not exceed 7, so there can be at most 7 matches. • If the forwarding table is partitioned into several TCAMs so that there is no ancestor-descendant relation in each partitioned TCAM, then it is guaranteed that there exists at most one match in each TCAM.

18. Design of the Proposed Architecture(2/4) • Proposed IP Lookup Architecture

19. Design of the Proposed Architecture(3/4) • Each of TCAM0 to TCAM6 should contain a disjoint set of prefixes. So the result of lookup for a given IP address will be no more than one match in each TCAM. • Obviously, the single-match TCAMs don’t have priority encoder logic. • The selection logic selects longest one among those matches by using length data and sends out the corresponding output port number.

20. Design of the Proposed Architecture(4/4) • In case that there is no suitable singlematch TCAM for a new inserting prefix, the conventional TCAM will be assigned. • Ex: There are only two single-match TCAMs and two disjoint prefixes p1=10100* and p2 = 1011* are stored in different single-match TCAMs. Then there is no way to insert a new prefix, p8=10* into any of the single-match TCAMs without moving an existing prefix.

21. Outline • Introduction • Related work • Propose IP Lookup Architecture • IP Lookup and Update Algorithms • Performance Evaluation • Conclusion

22. P1(10100*),10 P7(00*),15 TCAM0 P2(1011*),11 P4(010*),13 TCAM1 P1,5 Selection Logic P3(1110*),11 TCAM2 P5(100*),14 10 TCAM3 P6(110*),14 TCAM4 P8,2 P10(0*),18 P8(10*),16 TCAM5 P9(11*),17 TCAM6 Search algorithm • Ex: 10100100

23. P1(10100*),10 P7(00*),15 TCAM0 P2(1011*),11 P4(010*),13 TCAM1 P3(1110*),11 TCAM2 Available[0] ← true Available[0] ← false P5(100*),14 TCAM3 Available[0] ← false Available[0] ← true P6(110*),14 TCAM4 Available[0] ← false Available[0] ← true P10(0*),18 P8(10*),16 TCAM5 P9(11*),17 TCAM6 Available[0] ← true Available[0] ← false P9(11*),17 TCAM7 Conventional TCAM Insertion algorithm(1/3) Available[0] ← false • Ex: 101* Available[0] ← false Randomly Insertion 101* Available[0] ← false

24. P1(10100*),10 P7(00*),15 TCAM0 Available[0] ← false P2(1011*),11 P4(010*),13 TCAM1 Available[0] ← false P3(1110*),11 TCAM2 Available[0] ← false P5(100*),14 TCAM3 Available[0] ← false P6(110*),14 TCAM4 Available[0] ← false P10(0*),18 P8(10*),16 TCAM5 Available[0] ← false P9(11*),17 TCAM6 Available[0] ← false TCAM7 Conventional TCAM Insertion algorithm(2/3) • Ex: 1* Insert to TCAM7 1*

25. Insertion algorithm(3/3)

26. Deletion algorithm • For the prefix deletion it is needed to determine which TCAM contains the prefix p (As shown in line 1). • Then the prefix can be deleted from the TCAM (As show in line 2). • The function delete_from() is performed differently whether it operates on conventional TCAM or single-match TCAM.

27. Outline • Introduction • Related work • Propose IP Lookup Architecture • IP Lookup and Update Algorithms • Performance Evaluation • Conclusion

28. Simulation Environment(1/2) • In our simulation we used routing tables from Route Views[9].

29. Simulation Environment(2/2) • Comparison of Memory Movements

30. Simulation Results(1/3) • Memory Movements per Update

31. Simulation Results(2/3) • The Number of Prefixes in Each TCAM 0.33%

32. Simulation Results(3/3) • Insertions and Deletions 0.19% and 0.18%

33. Discussion • The updating performance is related to two factors • The number of updates in the conventional TCAM. • The number of deletions in the single -match TCAMs. • The simulation results show that the number of updates in the conventional TCAM is quite small.

34. Outline • Introduction • Related work • Propose IP Lookup Architecture • IP Lookup and Update Algorithms • Performance Evaluation • Conclusion

35. Conclusion • Novel assignment strategies for prefix insertion should be developed and evaluated in further research. • The design of the hardware to eliminate memory movements also remains for future work.