DNA design team update JinHyeock Choi Tero Kauppinen James Kempf Sathya Narayanan Erik Nordmark...
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Transcript of DNA design team update JinHyeock Choi Tero Kauppinen James Kempf Sathya Narayanan Erik Nordmark...
DNA design team update
JinHyeock Choi
Tero Kauppinen
James Kempf
Sathya Narayanan
Erik Nordmark
Brett Pentland
Design Team:
Brett Pentland
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.
Assumptions
• Layer-2 triggers to initiate RS message will be available.– RS delay is an issue?
• Routers on a link can hear each other.– Link = broadcast domain
• 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.
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.
Checking for Link Change
• 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
Getting the RA quickly
• Fast Router Discovery (RA caching)
• Simple FastRA
• Deterministic Fast RA
• Hash-based deterministic Fast RA
• Probabilistic Fast RA
Checking for Link Change
Explicit Link Identifier - Random
• Agreement on a random number as 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 a new option in RA messages.
Explicit Link Identifier - Random
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.
PIO (Prefix Information Option) Link Identifier
• Agreement on using a particular prefix as an explicit link identifier 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.
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.
PIO (Prefix Information Option) Link Identifier
• Hash of all active prefixes on the link to create a Link Identifier.
• Include this identifier in a new option in RA messages.
Hashed Prefix Link Identifier
Hashed Prefix Link Identifier
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• All prefixes must be
known to all routers.– Any variation makes the
identifier unrecognisable
• Link Identifier needs to change as prefixes on the link change.
Complete RA
• 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 RA
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).
Requested landmark
• 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
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.
Priority landmark
• 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
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.
Hybrid landmark
• Hybrid of requested and priority landmark.• Keep the possibility of another router providing
definite answer on link change.
Hybrid Landmark
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.
Getting the RA Quickly
Fast Router Discovery
• Cache recent RA messages in Access Points.• Access points forward RA message when hosts
associate with them.
Fast Router Discovery
Pros• Potentially very fast.• No changes to IP
routers or IP hosts.
Cons• Link specific.• Some security
concerns.• No changes to IP
routers or IP hosts – Why standardize? Why @ IETF?
Simple Fast RA
• Administratively configure one router to respond immediately.
Simple Fast RA
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?).
Deterministic Fast RA
• 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
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?
Negotiation-free Deterministic Fast RA
• 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
Pros• As for Det Fast RA• 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.
• Synchronized/secure knowledge of router tokens desirable.
Probabilistic Fast RA
• 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
Pros• As for Det Fast RA• 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.
Putting things together (Examples)
Requested Prefix/Negotiation-free Deterministic FastRA
• 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.
Priority Landmark/Probabilistic FastRA
• 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.
CompleteRA /FastRA
• 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.
Prefix LinkID/FRD
• 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.
AnalysisFiltering criteria
Generic Considerations
• Signalling overhead
• Interoperability with security schemes
• No additional security hole
• Interoperability with non-supporting nodes
Checking for Link Change
• Negotiated Vs non-negotiated.
• Security/Trust requirements between routers.
• Dependence on solicitation.
• Knowledge of all prefixes in all routers – Synchronization required.
• Multicast RA possible.
• Priority to current router.
Checking for Link Change (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.
• Graceful recovery from changes in link configuration state.
Getting the RA quickly
• New signalling mechanism?
• Access point involvement?
• Negotiated vs non-negotiated?
• Security/trust requirements between routers?
• Delay?
• Dependence on information in RS messages?
Where to now?
Where to?
• Any schemes not yet considered?• Develop the filtering criteria.
– Levels of importance?
• Apply filtering criteria.– Around 35 combinations possible so far.– No obvious winning combination.– Need to prune the field down to a small number.
• Sort out the details.• Implementation bake-off?• Should the DT continue down this path?
Recent Developments
• Removing:– Link detection:
• Explicit LinkID – random• Explicit LinkID – prefix
hash• Priority Landmark
– Fast advertisement:• Simple FastRA• Deterministic FastRA
• This leaves:– Link detection:
• Explicit LinkID - agreed prefix
• CompleteRA• Requested Landmark• Hybrid Landmark
– Fast advertisement:• Fast Router Discovery• Hash-ordered FastRA• Probabilistic FastRA
• Some techniques probably not worth pursuing due to incompleteness or complexity of negotiation.
Thankyou.