[Hipsec-rg] Re: Native HIP API questions in the hipsec-rg meeting

[[e-mail] (Lars Eggert)]

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Miika,

Miika Komu wrote:
>>
>>Lars Eggert:  Why are you binding to a src interface rather than
>>address?
>>
>>Joe Touch:  Binding to interfaces doesn't make sense.  Interfaces have
>>multiple IP addresses.  A single host identity must be able to bind to a
>>particular IP address, for policy reasons.
> 
> Actually, the binding is done on the source endpoint descriptor. The
> resolver communicates the descriptor to the HIP module and associates it
> with a (given) interface.
> 
> The main motivation for preferring IP addresses instead of interfaces is
> related to the probable life time of the identifiers. IP addresses are
> more unstable than interfaces, so interfaces were preferred. It is still
> possible to use a specific IP address by specifying the protocol family
> (and prefix) of the IP address to the resolver.
> 
> (Btw, usually client apps do not bind explicitly and server applications
> bind to INADDR_ANY or IN6ADDR_ANY, so this question may not be so
> important.)
> 
> Other opinions? Does anyone think that using interfaces instead of
> IP-addresses is a better approach? Or a no-go?

now I'm confused. The slides in San Diego showed a binding from HITs to 
interfaces. Yet this email talks about binding HITs to IP addresses. 
Which is it? Were the slides in San Diego wrong?

The issue we raised in San Diego was that *nothing* in the current 
sockets API ever binds to interfaces. Everything binds to IP addresses. 
Even INADDR_ANY just means "any IP address."

A HIP API would do well to follow this approach. The reason is that an 
outgoing interface is determined for each packet independently based on 
a routing lookup at transmission time. Which means that when the routing 
table changes, implementations don't have to go through all bindings to 
change their interfaces.

Additionally, as Joe pointed out, interfaces can have aliases, and 
furthermore, those aliases may move from one interface to another during 
the lifetime of a connection. Binding to IP addresses instead of 
interfaces avoids all this update mess.

> Another question to all: do you prefer "endpoint descriptors" instead
> of HITs as the AID and why?

Are there other kinds of endpoint descriptors than HITs? If yes, use the 
generic term. If no, just use "HITs" to be clear. (My two cents.)

>>Andrew McGregor:  Agree about not binding to an interface.  You may want
>>to bind to a HIT and use a setsockopt() to associate a locator with it.
> 
> Resolver does the setsockopt() on the behalf of the user. The difference
> is that the HI-to-IP mapping is "global" instead of socket specific. The
> security issues are dealt by tagging the mapping with the UID and GID.

I don't recall Andrew's exact question, and the above doesn't mean 
anything to me. Could you please elaborate?

>>Tim Shepard:  What if no DNS?  Nervous about building in dependencies on
>>DNS.
>>
>>Julien:  use /etc/hosts.  Can fall back to opportunistic mode too.
> 
> The other alternative for DNS is the DHT, but it remains to be seen if we
> ever get there. In the mean time, we should rely on DNS, as there are no
> real alternatives currently available.
> 
> Maybe the resolver should should support DHT queries too. With a new
> resolver, this should not be a problem. I'll have to look at this topic
> when I get my hands on a DHT DNS replacement implementation...

See Tim's email. I agree with him that finding a way to use HIP without 
a deployed DNS would be very useful. How do you bootstrap communication 
if someone hands you just a HIT?

Lars
-- 
Lars Eggert                                     NEC Network Laboratories

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