Re: Review of draft-ietf-trill-over-ip-08

Joe Touch <touch@isi.edu> Thu, 05 January 2017 18:45 UTC

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Subject: Re: Review of draft-ietf-trill-over-ip-08
To: Donald Eastlake <d3e3e3@gmail.com>
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From: Joe Touch <touch@isi.edu>
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Date: Thu, 5 Jan 2017 10:44:37 -0800
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Hi, Donald,


On 1/4/2017 5:43 PM, Donald Eastlake wrote:
> Hi Joe,
>
> Thanks for the comments.
>
> On Tue, Jan 3, 2017 at 1:56 PM, Joe Touch <touch@isi.edu>; wrote:
>> - the use of two different ports invites some potentially unintended
>> problems, e.g., selective blocking of the control vs. data plane. IMO,
>> given that TRILL's purpose is to extend Ethernet (not IP), this service
>> would be better served using a single port and differentiated
>> encapsulated traffic by whatever method TRILL nodes use internally.
>> Otherwise, this spec needs to include specific description of unexpected
>> behavior, e.g., data frames on the IS-IS port and IS-IS frames on the
>> data port.
> I guess I don't see this.
It's a configuration issue - what happens when (not if) a sysadmin opens
up one port but not the other?

IMO, unless there's a reason for that sort of selective filtering or
there's a specific need to encapsulate the traffic differently, these
ought to be treated as a single service - TRILL UDP encapsulation.

It's only inside the TRILL system that the difference between data and
IS-IS is useful and this encapsulation will have no effect on those nodes.

> As for selective blocking, if someone can control the passing of
> traffic through links connecting TRILL switches, they can always block
> a subset of traffic based on whatever criteria they want. I don't
> think it makes significant difference what header field they look at.

I'm thinking of the increased complexity and potential for failure by
not "fate sharing" data and IS-IS traffic.

> Similarly, if someone can modify traffic passing through links between
> TRILL switches, if the traffic is IP they could swap around port
> numbers, but they could also swap around other header fields.
> Presumably it is a policy decision for network managers based on their
> threat model whether or not to use facilities by TRILL or otherwise to
> provided to secure control traffic and/or use link security to protect
> all traffic over a link. (Similarly, it is a matter for end system
> users/managers to decide whether to use end-to-end security.)
I'm asking whether you actually expect or want IP transit nodes to treat
data and IS-IS traffic differently - via different routes, different
drop policies, etc. If not, then there's no benefit from having two
service ports.

> I suppose we could throw in a few sentences saying that if security is
> not being used and data or control is mislabeled as the other and it
> happens to be parseable as the other, you will get junk in the data
> stream or screwed up control information. 
TRILL data and IS-IS is already treated differently inside a TRILL
campus, e.g., by their existing headers. I can't see data being treated
as IS-IS or vice versa inside the campus, regardless of which port the
traffic arrives on.

That's largely my point - if the encap/decap node wouldn't need to treat
these differently in either direction (leaving or entering the TRILL
campus), then they're one service.

> But I don't think the
> mislabeling of control and data as the other by TRILL code is a
> realistic problem. It would be detected by the crudest of testing.

It *can* be detected, but your protocol needs to specify the correct
behavior. Is the UDP tunnel ingress/egress supposed to prevent such
mislabeling on ingress? If so, why would it care? If not, then again
there's no point to two services.

Joe