On Monday, 25 March 2019 19:31:24 CET Yoav Nir wrote: > > On 25 Mar 2019, at 19:23, Hubert Kario <hka...@redhat.com> wrote: > > > > On Monday, 25 March 2019 14:58:29 CET Yoav Nir wrote: > >> Yeah, so this looks very much like the IKE mechanism (the draft even says > >> so) > >> > >> In IKE the reason for this is to detect NAT because IPsec does not > >> traverse > >> NAT. We need to detect the NAT so as to choose an IPsec variant that > >> traverses NAT. If the server (or IKE Responder) lies, you might use the > >> NAT Traversing method when it’s not required, or if the server is really > >> good at lying, you might not use NAT Traversal when you should. > >> > >> With the proposed TLS extension, I would like to see a better analysis > >> for > >> what happens if the server lies. What happens if the client uses the > >> answer to do geolocation? We can easily take this to a “gay kid in > >> Uganda” > >> scenario. > >> > >> But I think the more interesting question is why do it at this layer? > >> Why > >> not use some web service such as the API version of > >> https://www.whatismyip.com <https://www.whatismyip.com/> > >> <https://www.whatismyip.com/ <https://www.whatismyip.com/>> ? The > >> answer is a property of the device, not to the socket. We might as well > >> have the device figure this out. > > > > how is it property of device? at best, it's a property of a LAN. And a LAN > > may have multiple Internet uplinks, every other connection may end up > > with a different IP (albeit from a small pool), so a public IP of any > > particular connection does not reliably indicate public IP of subsequent > > connections. > It’s perhaps a property of the device at the current connection > configuration. Pretty much any consumer device will have a preferred > network where the default route is. Any phone with a metered and a > non-metered connection will prefer the non-metered connection, and PCs will > use the link where the default route is. It is a reasonable approximation > to assume that the web service connection to whatismyip will follow the > same path as your other TLS connection. > > Servers may have more complicated routing tables, where the “regular” TLS > connection might be using a dedicated link while the connection to > whatismyip is going to the “Internet”. I don’t think this is the scenario > that this draft is working on. > > An interesting twist even for consumer devices may be where one of the two > connections chooses IPv4 while the other chooses IPv6. In that case, they > might end up on different links if, for example, the metered connection > offers IPv6 while the non-metered connection does not, or vice versa.
I already gave you an example of situation where that's not the case. You can have a router with two Internet links that routes the connections to a different ISP either based on a round-robin fashion or as a fallback when a connection dies. Neither of which would be visible to the device connected to a WiFi behind such a router. The client in the context of this I-D. -- Regards, Hubert Kario Senior Quality Engineer, QE BaseOS Security team Web: www.cz.redhat.com Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic
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