Re: [quicwg/base-drafts] disable_active_migration with SPA (#3765)

Kazuho Oku <> Wed, 17 June 2020 23:42 UTC

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Date: Wed, 17 Jun 2020 16:42:09 -0700
From: Kazuho Oku <>
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Subject: Re: [quicwg/base-drafts] disable_active_migration with SPA (#3765)
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> And then there is still another case -- using an anycast address as the handshake address and landing on a server deep inside your provider network. You will want to use SPA to avoid a risk of anycast route change during a long-lived connection.

Could you please elaborate why it is beneficial to migrate from an anycast address to SPA in this particular case?

It is my understanding that this is about a server located in an ISP network, hosting an anycast address and a preferred address. I would assume that that server is only reachable from client within that ISP, regardless of the address being the anycast address or the preferred address.

Assuming that is the case, migrating to a preferred address does not improve the chance of *each connection* surviving across unintentional client address migrations. Regardless of if the client uses the original address or the preferred address to designate the server, the connection survives while the client stays in the ISP network. If it goes out, then the connection dies regardless of the server address being used.

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