Re: [IPsec] Maximum sizes of IKEv2 messages and UDP messages ?

[Paul Wouters <[e-mail]>]

On Thu, 18 Jun 2020, Dang, Quynh H. (Fed) wrote:

> I don't know 10,000 or 20,000 users trying to connect to a VPN server around the same time where each pair is 300 kilobytes or more would have a
> noticeable impact or not. It depends on many factors I think. One of the factors is how the server stores those data for its computations. 
> 
> Let's say each pair is a 0.5 megabyte, 20,000 users would be around 10G of memory/storage. So, the over all performance impact could be
> noticeable once in a while for some VPN network.  

If you need that much memory to keep state, I don't think it matters
exactly how you receive and send that using IKEv2? Perhaps some
post quantum algorithms are better in that you dont have to keep
so much state during the exchange? And that could be a reason to
favour those. But you are far more qualified to judge that, than I am.

The intermediate exchange allows you to have many additional round trips
if that helps you reduce CPU or memory use. So I think from an IKEv2
point of view, that is all the scaffolding we need to provide. When
the new algorithms appear, we can go and implement those in a new RFC,
using the intermediate exchange.

I think Valery also had some ideas on how in the future, we could avoid
doing a hybrid key exchange with a classic DH that just costs CPU and
no longer gets us any security.

Paul