DNA design team update

1. DNA design team update Brett Pentland – Monash University

2. Progress • Identified and catalogued a range of solutions. • Discussions have centred on the pros and cons of available techniques. • Next steps: • Solicit more new ideas. • Develop of list of filtering criteria. • Apply filtering and choose a particular set of ideas. • Iron out the details.

3. Assumptions • Layer-2 triggers to initiate RS message will be available. • RS delay is an issue? • Routers on a link can hear each other. • Hosts that can connect to multiple links from one interface can distinguish packets from the different links. • DNA is complete when the link identity decision is made and the information required for IP configuration obtained.

4. The Problem • Checking for link change. • Putting the right information in the RS/RA exchange so that an accurate decision can be made after reception of the first RA. • Getting the RA fast.

5. RS/RA Exchange • Adding something to the RA: • Explicit Link Identifier • Random • PIO based • Hashed Prefix based • Complete RA • Adding something to the RS to ask a question: • Prefix-based Landmark • Priority Landmark • Hybrid Landmark

6. Getting the RA quickly • Fast Router Discovery (RA caching) • Simple FastRA • Deterministic Fast RA • Hash-based deterministic Fast RA • Probabilistic Fast RA

7. RS/RA Exchange

8. Agreement on an explicit link identifier between routers. LinkID MUST be different from LinkID of all links from which a host could directly transition from. Include this identifier in RA message. Explicit Link Identifier - Random

9. Pros Easy for host to recognise link reliably. Doesn’t require solicitation to be useful. Independent of prefix changes on link. Single (sol/unsol) RA will in one swoop help all hosts. Cons Establishing agreement between routers. Ensuring uniqueness from adjacent links. Extra option in RAs. Explicit Link Identifier - Random

10. Agreement on using particular prefix as LinkID between routers. Try to find a prefix common to all routers. If not possible, need some kind of option to add where the LinkID is not a configured prefix. PIO (Prefix Information Option) Link Identifier

11. Pros Easy for host to recognise link reliably. Doesn’t require solicitation to be useful. No extra options if there is a common prefix. Single (sol/unsol) RA will in one swoop help all hosts. Cons Needs agreement between routers if single prefix is chosen. Link Identifier may need to change as prefixes on the link change. Synchronization. PIO (Prefix Information Option) Link Identifier

12. Hash of all active prefixes on the link to create LinkID. Include this identifier in RA message. Hashed Prefix Link Identifier

13. Pros Easy for host to recognise link reliably. Doesn’t require solicitation to be useful. Single (sol/unsol) RA will in one swoop help all hosts. Cons Needs agreement between routers. All prefixes must be known to all routers. Link Identifier needs to change as prefixes on the link change. Synchronization if prefix change. Hashed Prefix Link Identifier

14. Routers learn about all prefixes on the link. Include all the prefixes on the link in RA messages. Flag to indicate completeness. Prefixes not explicitly configured on router recognizable as such. Complete Router Advertisement

15. Pros Easy for host to recognise link reliably. Small RAs if all routers on a link have the same prefixes. No changes to solicitations. Single (sol/unsol) RA will in one swoop help all hosts. Cons RAs carry extra prefixes if routers have non-matching prefix sets. Potential for large increase in RA size. Synchronization if prefixes change (less stringent). Complete Router Advertisement

16. Routers learn about all prefixes on the link. Hosts include a current prefix in their RS message. Responding routers include ‘yes/no’ flags to indicate if that prefix is in use in the link. The order of the responding routers is left to fastRA schemes. Requested landmark

17. Pros Simple RAs (yes/no flags). No router negotiations. Just listen to RAs. Cons Needs solicitation to be useful. Best suited for unicast RA. Aggregation gets tricky. Need to ensure all prefixes are known to all routers – synchronization –(or) Choice of responding router could lead to erroneous conclusions. Prefix option added to RSs. Requested Landmark

18. Hosts include their current prefix and current default router address in their RS message. Current default router has higher probability (=1) of responding to RS message. If current default router not present – a fast RA mechanism ensures arrival of a RA message from one of the router on the link. Priority landmark

19. Pros No modification to RAs. No router negotiations. Just listen to RAs. Can confirm bi-directional reachability of default router if no movement. Cons Relies on RA scheme that ensures that first response is from requested router if present. IPR Considerations. Adds router address option to RSs. Priority Landmark

20. Hybrid of requested and priority landmark. Keep the possibility of another router providing definite answer on link change. Hybrid landmark

21. Pros Simple RAs (yes/no flags). No router negotiations. Just listen to RAs. Can confirm bi-directional reachability of default router if no movement. Allows any router to respond giving definitive answer to link-change question. Cons Best suited to unicast RAs. Aggregation gets tricky. IPR Considerations. Adds router address option to RSs. Hybrid Landmark

22. Getting the RA Quickly

23. Cache recent RA messages in Access Points. Access points forward RA message when hosts associate with them. Fast router discovery

24. Pros Potentially very fast. No changes to IP routers or IP hosts. Cons Link specific. Some security concerns. Fast Router Discovery

25. Administratively configure one router to respond immediately. Simple Fast RA

26. Pros Simple. Cons Needs mechanism to select fast router – administrative config. Single point of failure. Unbalanced loading of routers. Will NOT work with priority landmark (Is this a Con?). Simple Fast RA

27. Routers on a link negotiate amongst themselves an ordering for responding to solicitations. Responses are made in order at fixed intervals starting from zero delay for the first router. Deterministic Fast RA

28. Pros No inherent single point of failure. One lost RA may not cause much of a slow down. Cons Relatively complex negotiation. Unbalanced loading but fairly simple to change that. Security requirements among routers? Deterministic Fast RA

29. Routers listen to other routers on link and create a token for each of them. XOR token with some ID of the received RS message (TSLLAO) and create ranking for response. Negotiation-free Deterministic Fast RA

30. Pros Routers just need to listen to determine their delay for a given RS. Cons RS needs to include some variable data like a TSLLAO. May be able to use source address if not :: and OptiDAD in use. Link local prefix and manufacturer ID’s could be common? Collisions? Synchronized/secure knowledge (router token) is a MUST? Negotiation-free Deterministic Fast RA

31. Listen for RA to learn number of routers on the link (bounded by MIN and MAX). When RS is received, calculate probability of response in particular slot based on the number of routers using pre-defined function (Loaded towards slot 0). Probabilistic Fast RA

32. Pros Routers just need to listen to determine their delay. No negotiation. No security required between routers. Cons Some responses will be delayed (a small amount). IPR Considerations. Probabilistic Fast RA

33. Putting things together (Examples)

34. Routers listen to RA messages and learn supported prefixes and IID of others routers – generate token based on the IID. Host include TSLLAO and a current prefix in the RS message. Router response ranking is created by XOR of TSLLAO with tokens of each router. Router responds with Yes/No flags to indicate the presence of the prefix identified in the RS in order of their ranking separated by pre-defined time-slots. Requested Prefix/Negotiation-free Deterministic FastRA

35. Routers listen to RA messages and learn number of routers on link. (Restricted by MIN and MAX). Hosts include current prefix and current router address in the RS message. If current router present in the link, will respond with RA message at slot = 0. Other routers respond at slot = [1..N] using a probability function of number of routers on link. Hosts will assume link change if first response is not from current router. Priority Landmark/Probabilistic FastRA

36. Routers listen to RA messages and learn supported prefixes of others routers. Host sends RS message. Pre-configured router responds with complete list of prefixes on link included in the RA message. All other routers respond after random delay between 0..500 ms, with complete list of prefixes in the message. Host assumes link change if its current prefix is not included in the complete prefix list. CompleteRA /FastRA

37. Routers negotiate among themselves to identify one prefix as the LinkID for the link. Access points cache recent RA message(s). Host attaches to a new Access Point. Access point transmit cached RA message to host. Based on linkID host knows whether it has moved. Host is on the same link – L2 trigger. Host sends RS message. Routers respond within 0..500 ms random delay. Based on linkID host knows that it has not moved. Prefix LinkID/FRD

38. AnalysisFiltering criteria

39. RS/RA Exchange • Negotiated Vs non-negotiated. • Security/Trust requirements between routers. • Dependence on RS message. • Knowledge of all prefixes in all routers – Synchronization required. • Multicast RA possible. • Priority to current router.

40. RS/RA Exchange (Contd.) • Definitive answer from other routers (useful when there is packet loss?). • Efficient when no change of link. • Bi-directional reachability verification. • Dependence on information on RS messages.

41. Getting the RA quickly • Access point involvement. • Negotiated vs non-negotiated. • Security/trust requirements between routers. • No timer induced delay or immediate response. • Dependence on information in RS messages.