DAD Optimization

Youn-Hee HanSamsung Advanced Institute of Technology

yh21.han@samsung.com

57th IETF, Vienna, AustriaJuly 13-18, 2003

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Why Optimized DAD?

RFC 2461 DAD “Nodes run a DAD algorithm on addresses before assigning

them to an interface.” “The DAD is performed on all addresses, independent of

whether they are obtained via stateless or stateful aucoconfiguration.”

Is it reasonable where all kinds of addressing domain?

MIPv6 DAD (draft-ietf-mobileip-ipv6-24.txt) “Currently, DAD needs to be performed for every new care-of

address as the mobile node moves, and for the mobile node's link-local address on every new link.”

Is it possible to support seamless L3 handover?

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Why Optimized DAD? Layer 3 Handover Delay in MIPv6 using RFC2462 DAD

1) IID is obtained from the interface hardware or generated randomly.

2) Generate an address and mark it “tentative address”3) Join solicited-node multicast group for the address4) Send NS5) Wait RetransTimer (default:1000) ms6) This solicit-and-wait process is repeated

DupAddrDetectTransmits (default:1) times

Get New Get New Network Network

PrefixPrefix

Duplicate Address Duplicate Address DetectionDetection

Send BUSend BU

move to new link

Get Layer 2Get Layer 2ConnectivityConnectivity

10001000msms

BU & BAckBU & BAckExchangeExchange

Send NSSend NS

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Is DAD Optimization in DNA?

DAD Optimizations aim to reduce delay due to Duplicate Address Detection in handovers

Existing work on this has no home. Stateless DAD schemes (e.g., Optimistic DAD)

• do not keep any information about DAD state in a node. Stateful DAD schemes (e.g., Advance DAD)

• keep information about DAD state in a node Constrained Addressing Domains

(DupAddrDetectTransmits=0)

Applicable for any systems wishing to send/receive immediately.

Network Attachment Detection often followed by address configuration.

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Stateless Proposal : Optimistic DAD(draft-moore-ipv6-optimistic-dad-02.txt)

The odds of IPv6 address collision are low Allow communication to be establish over a tentative

address, while attempting to minimize disruption in the case of collision.

With a tentative address, NA is sent with O flag = 0. If A neighbor already has a NC entry for that address, the NA

should be ignored.

NSs cannot be sent while an address is tentative traffic for unknown neighbors is redirected via the router.

The odds of IPv6 address collision can be calculated with

‘the Birthday Problem’(draft-soto-mobileip-random-iids-00.txt)

P(2^62,20)=< 7.8 e-17 P(2^62,100)=< 2.1 e-15 P(2^62,500)=< 5.4 e-14 P(2^62,1000)=< 2.2 e-13 P(2^62,5000)=< 5.4

e-12

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Stateful Proposal : Advance DAD(draft-han-mobileip-adad-00.txt)

Each AR (may be involved in Fast Handover) maintains a ‘Duplication-free CoA Pool‘. each address in the pool is in advance generated randomly

and tested for its uniqueness

On getting connectivity on a new link, MN gets a duplication-free address from its current AR Through a new option carried with RS/RA or NS/NA

exchanges.

[Passive-proxy-ND] For guaranteeing the uniqueness for addresses in the pool Never send NA for the address managed in a pool.

Never reply to any received NS for the address managed in a pool.

If the NS is for DAD, delete the specified address from the pool.

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Next Steps?

As MIPv6 matures, the need for reliable and fast address allocation and DAD schemes becomes critical to the goal of providing real-time data services.

Another Stateful Solution DHCP-related Optimized DAD using aDAD

Sufficient interest on the optimized DAD?

Need a Requirement Draft?

Any Comments?