Hi Ted,
Please see inline.
Cheers,
Med
De : Ted Hardie [mailto:ted(_dot_)ietf(_at_)gmail(_dot_)com]
Envoyé : samedi 4 mars 2017 00:49
À : BOUCADAIR Mohamed IMT/OLN
Cc : ietf(_at_)ietf(_dot_)org;
draft-hardie-privsec-metadata-insertion(_at_)ietf(_dot_)org
Objet : Re: Last Call: <draft-hardie-privsec-metadata-insertion-05.txt> (Design
considerations for Metadata Insertion) to Informational RFC
Hi Mohamed,
I've updated the draft and posted -07. I believe it includes all of the
elements on which we have already agreed. Some additional comments in-line,
once again with some snippage for readability.
On Fri, Mar 3, 2017 at 1:23 AM,
<mohamed(_dot_)boucadair(_at_)orange(_dot_)com<mailto:mohamed(_dot_)boucadair(_at_)orange(_dot_)com>>
wrote:
The intent is that it is information useful to those considering whether
restoring metadata lost to encryption in mid-network is the right way to go.
[Med] This is another assumption in the document that I disagree with: It seems
that you assume that an on-path device, that inserts metadata, is necessarily
RESTORING back that information. This is not true for many efforts:
• A Forward-For header inserted by a proxy does not restore any data;
it does only reveal data that is already present in the packet issued by the
client itself.
That's what restore means here.
[Med] Then, this needs to be defined in the document. I naively assumed that
“restored” is used to mean any piece of information that the client does not
want to insert in a packet, but an on-path device decides to inject it despite
there is no consent from the client. What you are describing is more about
“maintaining” or “preserving” information not restoring it.
If the information is present as metadata in the packet sent to the proxy but
would be absent as metadata under normal operation of the proxy, adding it back
in somewhere else restores the metadata.
[Med] “normal operation of proxy” is not a standard. A “normal operation of
proxy” would be to maintain the information sent by the client when relaying it
to the server. I’m sure you know for instance that SIP B2BUAs can do whatever
they want!
So origin IP address starts out in the IP header of the original packet but
gets pushed from that slot when the proxy constructs the onward IP packet to
the server. For it to reach the server, it has to be placed somewhere else in
the onward packet, restoring the lost metadata.
[Med] The client agreed to send packets with its source IP address (which mean
consent). Why the proxy would need to an extra channel to get consent for
relaying the source IP address to a server?
Had it been present in the packet as header value in the HTTP exchange, it
would not have been stripped by normal operation. There proxy operation
forwarding it on would be simply preserving it.
[Med] This is another question: whether the same or distinct channel can be
used to communicate the SAME data that was present in the initial packet issued
by a host.
• An address sharing device, under for example DS-Lite (RFC6333), that
inserts the source IPv6 prefix in the TCP HOST_ID option (RFC7974) is not
RESTORING any data. The content of that TCP option is already visible in the
packet sent by the host.
I agree with the IESG analysis of RFC7974. It does restore information by
taking information which normal operation would have elided and restores it.
[Med] The implication of what you are saying here is that proxies are good
because they hide the source IP addresses of host!
• Service Function Chaining WG
(https://datatracker.ietf.org/wg/sfc/about/) is defining an architecture to
communicate metadata by on-path devices; that metadata is inserted at the
network side. Border nodes will make sure that data is stripped before
forwarding packets to the ultimate destinations. The metadata can be a
subscriber-id, a policy-id, etc.
I'm afraid I don't have enough context to know what border node operations are
here, so this is difficult for me to comment on, but I hope the two examples
above clarify my thinking.
[Med] A BN is defined here : https://tools.ietf.org/html/rfc7665#section-4.4
So when draft-hardie-* says: “Do not add metadata to flows at intermediary
devices unless
a positive affirmation of approval for restoration has been received
from the actor whose data will be added.”
(1) Do you assume that the sample examples I listed above fall under your
advice?
(2) How an on-path device will know the data it intends to insert is a
“restoration”?
If the data is taken from a portion of the packet that would not normally be
forwarded to an upstream host and added to a portion that is forwarded to an
upstream host, then the device adding the data back in should know it is a
restoration.
[Med] That definition is not trivial as mentioned above. I would use “preserve”
or “maintain” rather than “restore”.
(3) Does it mean that for new data (i.e., that are not restoration), on-path
devices are free to do whatever they want? For me, this is undesirable. There
is a void there. A statement to require those networks to avoid leaking privacy
information must be included.
Brian Trammell has an ever growing list of side channels attacks, and this
document doesn't mean to cover that entire ground. It's advice for protocol
designers on what the privacy implications are of making the choice to use
network elements to carry this data.
Another assumption is made here:
Instead, design the protocol so that the actor can add such metadata
themselves so that it flows end-to-end, rather than requiring the
action of other parties. In addition to improving privacy, this
approach ensures consistent availability between the communicating
parties, no matter what path is taken.
This text claims that providing data by the endpoint ensures a “consistent
availability” of that information. This is broken for a multi-homed host that
uses for example Forward-For header: Obviously, the content of the header if
injected by the endpoint will depend on the path.
If the endpoint sends the data, data will be consistently available in that
header. The data changes, of course.
[Med] I’m not sure to follow you here. What is meant by “consistent
availability” then? Do you mean the same channel/procedure to communicate the
information? Or “consistent data”?
[Med] Resources may not be restricted to CPU or disk but may be granting access
to the service (e.g., download a file when a quota per source address is
enforced). It can be whatever the servers consider to be critical for them; it
is up to the taste of the service design to characterize it. The NEW wording
proposed above is technically correct. Please reconsider adding it to the draft.
I did consider it, but I continue to believe that it moves the needle too far
into simple server preference. I retained the original PSAP language in -07 as
a result.
[Med] emergency is only an example ; other services may exist that impose the
same trust model.
I also added a note about your extensive review. While you and I clearly have
some differences of view, the document has gotten better from your engagement
with it, and I appreciate your efforts.
[Med] I reviewed the -07. Although it is better compared to -05, I still don’t
think it is ready to be published as it is. Thank you for your effort.
regards,
Ted