Subject: RE: misconfiguring the tunnel source address [mech-v2-04]

From: "Follen, Stephen" <[email-masked]>
Date: Fri, 20 Aug 2004 08:16:46 -0400

On Fri, 20 Aug 2004, Pekka Savola wrote:
> I just checked 4 different implementations: Linux, BSD, Cisco and
Juniper.
> All of them "allow" the administrator to misconfigure the source
addresses.
> This would seem like a hint that the implementors want to give the 
> power to the administrators, or not bother with additional checks. I'd

> be interested if you know of implementations which check the tunnel
source
> address at configuration time?

The Enterasys implementation also does not check the tunnel source
address at tunnel configuration time, primarily because to do so would
be overly restrictive to the admin in terms of order of configuration;
The admin is allowed the flexibility to configure the tunnel first and
then configure the IPv4 interface if (s)he wants to - but that's just an
implementation detail.

IMHO this sort of stuff is not important enough to go into an RFC. It
seems obvious that if the tunnel source address does not exist on the
device, or if there is no route to the remote v4 destination, or ... the
tunnel won't work.

---

From: Alex Conta <[email-masked]>
Date: Fri, 20 Aug 2004 13:29:05 -0400

Follen, Stephen wrote:
> [...]

This so called "flexibility" to configure a tunnel without the existence 
a IPv4 interface, basically indicates that the box allows the creation 
of a virtual point to point link, and route(s) that are using it, when 
there is no physical connectivity to provide the basis for that link 
(and routes) to exist.

I do not see the advantage to the user, but can certainly see the 
headaches...

> 
> IMHO this sort of stuff is not important enough to go into an RFC. 

The spec promises a virtual point to point link between two nodes to the 
user. Configuring the tunnel following the spec, and getting a tunnel 
that does not work, is a spec bug.

> It

Specifications state often the obvious things to those who are 
knowledgeable. That does not mean they should not contain what could be 
  obvious to some.