DNA design team update

Brett Pentland – Monash University

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.• 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.

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

Getting the RA quickly

• Fast Router Discovery (RA caching)

• Simple FastRA

• Deterministic Fast RA

• Hash-based deterministic Fast RA

• Probabilistic Fast RA

RS/RA Exchange

Explicit Link Identifier - Random

• 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

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 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.

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

• Hash of all active prefixes on the link to create LinkID.

• Include this identifier in RA message.

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• 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.

Complete Router Advertisement

• 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

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.

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• 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?

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• 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.

• 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.

AnalysisFiltering criteria

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.

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.

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.