Re: [v6ops] draft-pauly-v6ops-happy-eyeballs-update-01

[Philip Homburg <[e-mail]>]

>I agree with both Lorenzo and Jordi here, there are multiple problems that 
>won't get fixed, having "hard" failures doesn't seem to help that much at 
>this time, but with the PMTUD failure mode as well (which might not be 
>discovered until TCP handshake is already done), what about adding 
>additional methods to try?
>
>"normal HE mode with IPv4/IPv6"
>If these fails, let's say 500ms
>"try NAT64 method" (what Lorenzo proposed)
>
>if these succeed but I'm not getting any data (for instance my GET / seems 
>to time out, no data for 5 seconds)
>
>then I try again but with TCP MSS 1200 and PMTU 1280 (I purposely went 
>below MSS 1220, perhaps there is no reason to).

I was very surprised to hear it, but there are already middle boxes close to
the customer edge (or in the CPE) that do MSS clamping for IPv6.

It is hard to quantify, but in IPv4 lots of potential PMTU problems are masked
by MSS clamping. 

Given that on the whole we failed to have PMTU blackhole detection/avoidance
deployed at large on the server side, using MSS clamping will be the most
effective way to deal with this problem.