Re: [secdir] Secdir review of draft-ietf-i2rs-architecture-07

"Susan Hares" <shares@ndzh.com> Thu, 17 December 2015 00:54 UTC

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From: "Susan Hares" <shares@ndzh.com>
To: "'Charlie Kaufman'" <charliekaufman@outlook.com>, <secdir@ietf.org>
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Subject: Re: [secdir] Secdir review of draft-ietf-i2rs-architecture-07
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Charlie: 

 

I'm hoping you will help us review the result of a year's work on security
in the I2RS WG that relates to the i2rs architecture document.  After your
review, we decided to progress by defining the security requirements for the
protocol requirements and for the environment.  We also defined security
requirements for the protocol. 

 

http://datatracker.ietf.org/doc/draft-ietf-i2rs-security-environment-reqs/

http://datatracker.ietf.org/doc/draft-ietf-i2rs-protocol-security-requiremen
ts/

 

In addition to our security requirements, we defined requirements for the
protocol regarding publication of notification streams, ephemeral state, and
logging/traceability.  

 

http://datatracker.ietf.org/doc/draft-ietf-i2rs-pub-sub-requirements/

http://datatracker.ietf.org/doc/draft-ietf-i2rs-traceability/

http://datatracker.ietf.org/doc/draft-ietf-i2rs-ephemeral-state/

 

The I2RS WG thanks you for your excellent review and suggestions to make
this protocol better.   We hope that this combination of documents will
provide you feedback on our work in the last year. 

 

Cheerily, 

 

Sue 

 

-----Original Message-----
From: Charlie Kaufman [mailto:charliekaufman@outlook.com] 
Sent: Monday, December 22, 2014 3:05 AM
To: secdir@ietf.org
Cc: draft-ietf-i2rs-architecture.all@tools.ietf.org; iesg@ietf.org
Subject: Secdir review of draft-ietf-i2rs-architecture-07

 

I have reviewed this document as part of the security directorate's ongoing
effort to review all IETF documents being processed by the IESG.  These
comments were written primarily for the benefit of the security area
directors.  Document editors and WG chairs should treat these comments just
like any other last call comments.

 

As an "architecture" document, this document does not specify the details
that would allow one to review whether the security mechanisms were
adequate. The Security Considerations section correctly notes that there is
a need to transport this protocol over something that provides mutual
authentication, confidentiality, and integrity to the data. It also notes
that there needs to be some authorization mechanism that configures which
authenticated clients are allowed to make what requests. There is no
discussion of where this authorization comes from, and in particular whether
the authorization data can be viewed or manipulated using this protocol,
though my sense reading the document is that authorization data would be
configured and manipulated by some other mechanism (as would the
manipulation of client and server credentials). So I think we need to wait
for the successor document with more meat to judge.

 

Sue: Authorization comes from outside the protocol in a AAA or proprietary
protocol.  We hope the two security documents provide the detail on this
protocol. 

 

That said, I would ask the designers some leading questions of the form
"Have you considered.". Some relate to security and some don't. I'm not the
best person to judge the answers, but I'm hoping the questions will kick off
some discussion within the working group. It's likely that some of these
issues have already been adequately discussed, in which case feel free to
ignore them.

 

This document goes out of its way *not* to specify any security mechanisms
in order to provide flexibility to implementers. That makes sense for a
requirements document, but I'm not sure it makes sense for an architecture
document. You are clearly going to need some security mechanisms, and for
clients and agents to interoperate, they need to be standardized. My guess
is that you will end up using SSL with either client certificates or with
some lesser client to agent authentication mechanism inside an SSL
connection with only a server certificate. The mechanism you choose will
determine the formats of the identity information you get and use to do
lookups in your authorization tables. But section 7.1 says the protocol may
need to run over TCP, SCTP, DCCP, and possibly other link types. Do you
envision different security mechanisms for the different protocols?

 

Sue:  Yes, we will use different security mechanisms per protocol.  We
envision that we will be using secure encrypted exchanges over
NETCONF/RESTCONF for all configuration data, and many pub/sub requirements.
You will find we define these protocols.  We may utilize other existing IETF
but these exchanges will require secure encrypted sessions.  There is one
exception to this process.  We may for a specific data model allow an
insecure connection for some data.  However, this data model and its
protocol will be sent to the security directorate for specific review and
approval. 

 

In the third paragraph of section 4 (and in some other places), you talk
about the I2RS Client acting as a broker forwarding requests for some other
entity, and forwarding some opaque identifier of that requesting entity to
the I2RS Agent for logging. This presumes that the I2RS is configured with
(or has access to) the authorization information that says which requestors
are permitted to do which operations. A useful extension to the protocol
would be to be able to forward a requestor-identity string that the Agent
not only logs but also checks for proper authorization before performing the
requested operation. The Agent would need to verify that both the Client and
the client asserted identity of the requestor be authorized to perform the
operation. This relatively simple change to the Agent and the protocol might
permit a considerably simpler client (if this brokered-request behavior is
actually common).

 

Sue:  On the broker, I believe the text in section 4 is the one below:  

 

  If the I2RS Client is acting as a broker for multiple applications, 

   managing the security,

   authentication and authorization for that communication is out of

   scope; nothing prevents I2RS and a separate authentication and

   authorization channel from being used.  Regardless of mechanism, an

   I2RS Client that is acting as a broker is responsible for determining

   that applications using it are trusted and permitted to make the

   particular requests.

 

We queried the WG on your idea.  They felt the broker would not be the
majority of work initially.  The WG appreciated your suggestion, the WG
suggested it was a feature for version 2.  We will be starting the
requirements for Version 2 in 2016. 

 

Section 1.1 says I2RS is described as an asynchronous programmatic
interface. Asynchronous usually means that you can launch operations and
then check back later whether they successfully completed. If you want to
execute a second operation only if a first succeeds (or to guarantee the
order in which they execute), you need to at some point wait for operations
to complete. There is also substantial overhead in supporting asynchronous
operation in that all transactions need labels so that they can be queried?

 

Have you done that? A conceptually simpler strategy is to say that since a
client can make multiple parallel connections to an agent that in cases
where a client wants asynchronous operation he opens multiple connections
and launches one asynchronous operation on each. The cost is that is has
lower performance in cases where there are large numbers of parallel
operations tying up lots of connection state.

 

Sue: We have added to the models response in order to support transactions.
In the RESTCONF version of the I2RS work, the client is launching one
asynchronous operation on each.  This matches your model.   However, since
NETCONF is widely deployed we are working to add enough in NETCONF
configuration work and pub/sub.  As to other protocol for pub/sub or
reception of data streams, we will begin this in 2016.  

 

Given that information, do we have enough in version 11 of the architecture
document? (see attached). 

 

Section 6.2: The restriction that this protocol injects only ephemeral state
seems surprising, especially given that the circumstances under which the
ephemeral state is lost are defined in terms of a network device reboot.

Some network devices may not have a clear notion of a reboot, or might do it
so rarely as to render such functionality useless. I was confused by the
discussion of agent reboots vs. device reboots. 

 

Sue: Routing devices often have some parts of software running in one
process.  Some routing devices have the capability of handling a software
module reboot (after failure or upgrade) rather than the whole process.  A
device reboot is considered the whole system reboot (hardware or software)
rather than just the process.    

 

In the VM world, there is the software reboot of the process and the "pseudo
hardware reboot" of the hosting system.  Again, these are normative for
routing in this environment (Google, Amazon,  Linked-in) 

 

The first paragraph seems to say that ephemeral state is lost when the
device reboots, but 6.2.1 seems to imply that state is lost when the agent
reboots. The sentence "Just as routing state will usually be removed shortly
after the failure is detected." seems to imply that ephemeral state might be
lost when a client reboots. Have you considered what happens to state when a
client disappears but the agent and server stay around forever. There is an
option later in the document for some sort of timeout, but I would think
there would be some sort of mechanism to guarantee that all ephemeral state
disappears eventually unless the requestor is still around implicitly
renewing it.

 

Sue: The ephemeral state is lost when the agent reboots (software) or when
the device reboots (hardware or software).  The guarantee of the state being
lost is a requirement for I2RS support.   The I2RS architecture specifies
two notification messages that are sent in the publication of notification
(see the pub-sub requirement document) 

 

With that said, we are mandating In the ephemeral state requirements
(http://datatracker.ietf.org/doc/draft-ietf-i2rs-ephemeral-state/) - that
ephemeral state resets on a reboot.  Any comments on the documents would be
helpful. 

 

Also in 6.2.1, it appears that one piece of state is explicitly not
ephemeral... the agent keeps a non-ephemeral list of clients to notify when
ephemeral state is lost. If the client is not accessible, for how long does
the agent continue to try to contact it? Forever?

 

Sue: The agent timing on keeping the non-ephemeral list of clients to notify
depends on the agent's implementation of the pub/sub requirements (
<http://datatracker.ietf.org/doc/draft-ietf-i2rs-pub-sub-requirements/>
http://datatracker.ietf.org/doc/draft-ietf-i2rs-pub-sub-requirements/).
The two notifications specified in 6.2.1 must be added any protocol handling
notifications via the pub-sub.  The notification requirements specify how
the client specifies these publication actions. 

 

The I2RS protocol security requirements describe how notification impacts
the protocol requirements. 

The security environment discussions should discuss how notification impacts
the over-security requirements. 

 

Please let me know if you think these documents are sufficient. 

 

The protocol requires that agents be able to open connections to clients (in
addition to clients being able to open connections to agents). This will
introduce lots of challenges. It means the client needs an open port to
accept connections, likely an SSL certificate, and will be in trouble if it
is behind a NAT or is mobile and does not have a stable IP address. Other
parts of the spec mention that two entities might have the same client
identity. In such cases, it will be tricky for the agent to connect to "the
right instance". It might be better to only allow clients to initiate
connections to agents, possibly with some sort of unauthenticated
notification from agent to client that initiating such a connection would be
a good idea (to reduce the overhead of the polling that would otherwise be
necessary).

 

Yes:  You are correct.  The two proposals in the NETCONF are the pub/sub
work 

https://datatracker.ietf.org/doc/draft-ietf-netconf-yang-push/

https://datatracker.ietf.org/doc/draft-voit-netconf-restconf-yang-push/

 

 

My first question when I started reading this document was why do we need a
new protocol. Wouldn't SNMP or NETCONF do this just fine? And there are
probably lots of others. Section 3.1 says "There have been many efforts over
the years to improve the access to the information available to the routing
and forwarding system." It would be good to understand why those efforts
failed before inventing some new syntax (when it is unlikely the syntax is
what killed previous efforts). Then section 7.1 says the protocol will be
"based on" NETCONF and RESTCONF. What does "based on" mean in this context?

 

Sue:  The OPS/NM are utilizing NETCONF/RESTCONF for yang data models.  The
I2RS is data-model defined based on the yang data models.   I2RS is a
combination of configuration functions, notification publication, logging,
and data analytics (e.g. IPFix or other data stream).  The key security
point is that with upgrades the NETCONF/RESTCONF may handle configuration,
some level of notification, and some level of logging/tracing.  It will not
handle massive data analytics that IPFIX might handle.   The setting of
config, pub/sub parameters for notification streams, and logging/tracing
will be initially done by NETCONF/RESTCONF.  If speed becomes an issue, we
will focus on this after getting some experience with the protocol. 

 

What killed SNMP was the MIB-II model is not supportable by human beings
over the long run.  This has been discussed and agreed upon in
NETCONF/RESTCONF and Yang - so it is not the place of this document to state
this point.   

 

 

Section 7.8 talks about "collisions", but it wasn't clear (at least to me)
whether these were collisions in the time sense where two requests are made
simultaneously by different clients vs. whether it is a case where once
client tries to override the setting of another client. I also wonder
whether there are cases where two changes would interact in some way other
than one of them winning, as when two clients each want to increment the
bandwidth of some virtual like over which they are both tunneling traffic
(and where the correct result is to add the two increments).

 

Sue: You are correct in your assessment.  We have set a priority on each
client, and a collision case for when two clients of the same priority
interact.  (First one wins and stays on until higher priority or client
disconnects).  Now, this part of the protocol was hotly debated and I expect
additional changes in a second version of I2RS with more analytics. 

 

The first version is to get NETCONF/RESTCONF with configuration, pub/sub,
logging, and a few analytic channels.  The second version will focus more on
this point.  We need to see what type of implementations issue come up and
get a security review of actual implementation issues. 

 

The last paragraph of 7.9 says "the protocol will include an explicit reply
to modification or write operations even when they fully succeed". How does
this relate to the asynchronous nature of the protocol?

 

Sue: The data-models are being designed to explicitly reply to modification
or write operations for key data elements.  The notification (pub/sub) will
be sent on the notification stream to notification clients if security and
filters allow it.  The logging will be sent on the logging stream to logging
clients if security and filters allow it.  

 

These occasional points of synchronization focus on the key data elements
per model. 

 

Good luck with this!

 

                --Charlie