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

Igor Lubashev <> Tue, 14 July 2020 16:29 UTC

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Date: Tue, 14 Jul 2020 09:29:42 -0700
From: Igor Lubashev <>
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Subject: Re: [quicwg/base-drafts] disable_active_migration with SPA (#3765)
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Thanks for showing the cases, @MikeBishop.

You can probably split second bullet into 2a (any change in 2-tuple can route to a different backend) and 2b (change to a different network can route to a different backend -- I am thinking of BGP-as-a-load-balancer).

So you have:

* (1) "don't change port" (but since clients are unlikely to deliberately try changing ports, it is "don't change address")
* (2a) "don't change address"
* (2b) "don't change network/interface"
* (3) "don't change network/interface"

Bullets 1/2a/2b are load balancer concerns, and are very different from bullet 3 case.  In fact, you can have deployments where both bullet 1/2a/2b and bullet 3 concerns are true at the same time.

SPA helps with bullet 1/2a/2b case by removing the load balancer from routing, when the server can provide its own direct IP address.  So bullet 1/2a/2b concerns no longer apply to any packet sent to SPA.

After/during a change to SPA, only case 3 ("don't change network/interface") can matter.

Before the change to SPA, what really matters is whether there is an SPA to change to.
* If there is an SPA, the client will likely change to it quickly, so it probably does not matter which option one chooses while on handshake address.
* If there is no SPA, "don't change network/interface" will probably be good enough, since changing addresses within the same network is rare.  But I can be easily persuaded to entertain a different pov here.

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