Reviewer: Jan Lindblad
Review result: Almost Ready
This is my YD review of
draft-ietf-i2nsf-consumer-facing-interface-dm-07. I
have previously reviewed the -05 revision (~end June). I find the new
revision
much improved, but still with much to discuss. I will call this
"almost
ready".
Generally speaking, I think the YANG module lacks the precision and
descriptions needed to foster interoperability. The examples at the
end
are
very enlightening however, and compensate for much of that, but their
informal
nature can never replace proper YANG. The module usage needs to be
mostly clear
from the module itself.
The management access control model proposed here is, even with its
latest
adaptation towards NACM, is still quite different from NACM author's
original
ideas. I will therefore bring this use case up in the NETMOD WG for
discussion.
1. Network access control principles
Network access control is about which users are able to use the
network
being
managed, for example connect to facebook. The purpose of the NSF
module
is to
control this access. This version of the YANG module is now based on a
list of
policies.
Each policy has a list of rules. Each rule has an event --
condition --
action
triplet. This resembles traditional firewall management, which is a
good
thing,
because that concept is stable and much tried. This allows
operators to
create
lists of rules in this style:
if pkt.x == 1: drop // Rule 1
elif pkt.y > 2: alert // Rule 2
elif pkt.z == 10: pass // Rule 3
else: drop // Rule 4
This pattern relies heavily on the ability to control the order of the
rules.
The current model relies on the alphabetical sorting of names rules
for
the
ordering. The YANG trick I would recommend to give operators the
ability
to
insert and move rules as they wish is to add ordered-by user on the
list:
list rule {
ordered-by user; // <== Add this line
leaf rule-name {
Nothing is said about what the system should do in case policies
conflict. What
if one policy says pass, the other drop for the same packet? Please
clarify.
What should happen to packets that do not match any of the policies?
This module also assumes that all users in the operator's organization
are
listed in one or more NACM groups (e.g. "employees"). That wasn't
really
the
NACM authors' original intent. Even if this could be made to work
maybe,
there
is no strong reason to repurpose the NACM group concept for user
network
access
purposes. It could easily be modeled differently. So in the cases
where
there
are leafrefs to NACM groups when dealing with network access rather
than
management access, don't use NACM groups.
leaf src-target {
type leafref {
path
/nacm:nacm/nacm:groups/nacm:group/nacm:user-name; //
<== Point to some other list of network users
2. Management access control principles
Management access control is about which users are able to
configure/run
actions/the policies and rules. IMO, the most controversial aspect of
this
module has always been its new and creative management access control
model. In
this revision, the management principles have been remodeled
greatly to
fit in
with NACM. I find this redesign very promising, but the result is
still
not
quite ready for publication.
The point where integration with NACM concepts is important is when it
comes to
allow some users to CRUD the NSF policies and rules themselves.
There is
now a
leaf-list "owners" on each policy and rule which point to a list of
NACM
groups. My understanding is that the idea is that the NSF module
should
be seen
as a service model that translate high level ownership information to
specific
NACM rules. It would be good to mention these ideas somewhere in
the NSF
document.
leaf-list owners {
type leafref {
path /nacm:nacm/nacm:groups/nacm:group/nacm:name;
I expect the intent is that any user listed in a NACM group
mentioned in
the
owners list would get full CRUD privileges for the contents of the
rule
the
owners leaf sits on. That is never spelled out anywhere, however.
It is a little less clear how leaf-list owners on policy objects
should
be
handled. Should owners listed on a policy object get full CRUD powers
over the
entire policy, including all the rules inside? Or would they need
to be
listed
on the rules as well? Not clear. Is the intent that users not
listed on
the
policy object are unable to create new rules, but to be able to update
rules
they are listed as owners of, if any?
Who is allowed to create new policy objects? Should users that are not
owners
get read access to all the policies and rules?
Finally, there is an "owner" leaf on each rule with an identityref
allowing
operators to configure a role name like dept-head or sec-admin. It is
marked
mandatory, but never included in any of the examples at the end of the
document. This makes me think this may be a remnant from bygone
times and
should be removed from the YANG. If not, an explanation of how to use
this
leaf, and how it interacts with "owners" needs to be added, and the
examples
updated.
3. leafrefs crosspointing between policy instances
There are six leafrefs that point to various objects inside a policy,
e.g. a
rule condition pointing to a device group name. None of them restrict
what can
be pointed to so that only names within the current policy are
valid. It
is
therefore possible to configure the name of a device group defined
in a
different policy. I suspect this is not the intention. In order to
restrict the
leafrefs to the same policy, the following predicate can be added:
leaf-list src-target {
type leafref {
path
"/i2nsf-cfi-policy[policy-name=current()/../../../../../policy-name]/endpoint-group/device-group/name";
// <== Add predicate
4. Mandatory to implement all events, conditions, actions
Each rule is defined with a choice of different events (admin, time),
conditions (firewall, ddos, custom, threat-feed) and actions (pass,
drop,
alert, mirror, ...). Is the intent that all of these options should be
mandatory to implement? The current model requires this. Also,
would it
make
sense to allow additional mechanisms here? If so, it may be good to
explain to
readers how the set of choices and identities can be extended by
implementations.
5. Optional and mandatory elements
In this revision of the module, 8 leafs have been marked mandatory. A
few of
them are list keys, which are conventionally not marked mandatory,
since
list
keys are always mandatory. A few others are skipped in the XML
examples
at the
end of the NSF document, which makes me believe they might not
really be
mandatory after all.
Three leafs have a default, but most leafs are left optional
without any
default. In many cases I think I understand what it means to not set a
leaf,
but with the ones listed here, I don't think it clear at all.
Either add
a
default to make it clear, make them mandatory if they should be, or
explain in
the leaf description what happens if not set.
493: leaf-list name
513: leaf-list protocol
531: leaf geo-ip-ipv4
541: leaf continent
562: leaf feed-server-ipv4
585: leaf payload-description
590: leaf-list content
600: leaf-list owners
870: leaf method
6. Indentation
The YANG indentation is mostly wrong. Run the YANG text through
pyang or
some
other tool that can indent the content correctly before you put it
into a
document.
7. YANG element naming
The YANG convention is to not have lists on the top level in the YANG
module,
but to surround lists with a container. The surrounding container
often
has a
name in the plural and the list in singluar, like this
container interfaces {
list interface {
To better fit into the world of IETF YANG modules, I'd recommend
turning
the
top level list i2nsf-cfi-policy into this instead:
container i2nsf-cfi-policies {
list policy {
Further down, I would change container rule to rules:
container rules {
list rule {
Finally, it is customary to not repeat the names of parent object
in the
names
of elements. For example, in the following:
list threat-feed-list
leaf feed-name
leaf feed-server-ipv4
leaf feed-server-ipv6
leaf feed-description
all the leafs should normally not repeat "feed-". Just leaf name, leaf
server-ipv4, leaf server-ipv6, leaf description. There are many more
examples
of this throughout the module.
The condition choice has many containers with a single leaf inside
(e.g.
ddos-source). Their purpose is rather unclear to me. Remove?
container ddos-source {
description
"This represents the source.";
leaf-list src-target {
Also, I find the name "src-target" rather confusing. How about
"source"?
8. No date leaf
The draft text near fig 2 talks about a date leaf. There is no date
object in
this revision of te YANG.
"Date: Date when this object was created or last modified"
9. leaf owner
Near fig.3 leaf Owner is mentioned. Is this leaf still current?
"Owner: This field contains the onwer of the rule. For example,
the person who created it, and eligible for modifying
it."
10. leaf packet-per-second
This is now modeled as uint16. Is this future proof? Many packet flows
on the
internet exceed 64k pps.
11. container custon-source
Misspelled. Should be custom-source
12. identity ddos
Is ddos a malware file-type? This is not exactly in line with my
intuition.
13. identity protocol-type
There are other modules that already define protocol-types. Would
it be
worth
reusing one of them?
14. identity palo-alto
Is it a good IETF practice to list vendor names in modules? Can we
consider
this a protocol name? Is there perhaps an RFC/specification name
for it
that we
could reference instead?
15. grouping ipsec-based-method
This grouping contains a list which allows listing none of, either
of or
both
of ipsecike and ikeless. Are all valid configurations?
16. leaf feed-name
This leaf is the key in a list, which makes it possible to have at
most
one
feed of each type. If it would make sense to configure more than one
feed of
the same type, the YANG needs to be updated here.
17. leaf-list content
This leaflist is of type string. What is the format of this string?
Does
the
name refer to something?
18. Event types
container event has a choice between enforce-admin and time
alternatives. Each
of those choices have a leaf that allows the operator to configure an
identityref to an enforce-type value. What does that mean? What
would it
mean
if an operator configured admin == 'time' (or enforce-time ==
'admin')?
19. leaf begin-time, end-time
>From the examples, it can be seen that these are meant to be a
time of
day
values. Currently they are modeled as yang:date-and-time, which means
they are
a concrete time a specific day, e.g. 2019-11-11T16:07. This needs
to be
changed
in order to be what the modeler intended. Perhaps like this:
typedef time-of-day {
type string {
pattern '(2[0-3]|[01]?[0-9]):[0-5][0-9]';
}
}
20. leaf frequency
This leaf is now modeled properly from a YANG perspective. But what
does
it
mean? If this leaf is set to 'once-only', what exactly will happen
only
once?
Please write a description that explains this.
21. Example in Fig.17
The example contains XML that refers to "endpoint-group/user-group".
There is
no such element in the YANG.
<endpoint-group
xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-cfi-policy">
<user-group>
Furthermore, there is nothing called range-ip-address,
start-ip-address,
end-ip-address. They are called range-ipv4-address,
start-ipv4-address,
end-ipv4-address.
<range-ip-address>
<start-ip-address>221.159.112.1</start-ip-address>
<end-ip-address>221.159.112.90</end-ip-address>
</range-ip-address>
Finally, there must not be any xmlns attribute on an closing XML
tag. So
</endpoint-group
xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-cfi-policy">
should be
</endpoint-group>
This happens in several of the examples.
22. Example in Fig.18
There is no element called policy any more. It's now i2nsf-cfi-policy.
<policy xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-cfi-policy">
<policy-name>security_policy_for_blocking_sns</policy-name>
The rules are modeled in a container and list, both by the name
rule. So
there
needs to be two <rule> tags.
<rule>
<rule-name>block_access_to_sns_during_office_hours</rule-name>
The security-event element is marked mandatory in the YANG, but
missing
in the
example. The times given below may be what is intended, but do not
match
the
date format for the type used (which include a date, etc).
<event>
<time-information>
<begin-time>09:00</begin-time>
<end-time>18:00</end-time>
</time-information>
</event>
Since the example is not mentioning leaf frequency, it will have the
value
'once-only'. Maybe explain what that means in the context of the
example?
The condition/firewall-condition says the src-target is mandatory and
dest-target optional, exactly like below.
condition/custom-destination/dest-target is mandatory and
src-target is
optional, exactly like below. Is this pure luck, or is there a logical
explanation why exactly those should be mandatory, and the example use
precisely those?
<condition>
<firewall-condition>
<source-target>
<src-target>employees</src-target>
</source-target>
</firewall-condition>
<custom-condition>
<destination-target>
<dest-target>sns-websites</dest-target>
</destination-target>
</custom-condition>
The current YANG model does not allow setting both a
firewall-condition
and
custom-condition. If that should be allowed, the model needs to
change.
Should
it be possible to have multiple firewall- or other conditions? That is
not
currently possible.
This example leaves out the mandatory leaf owner. Is that a sign
that it
should
not be mandatory, or perhaps not exist at all?
23. Example in Fig.19
This example lists a firewall-condition with no src-target, which is
mandatory.
<firewall-condition>
<destination-target>
<dest-target>employees</dest-target>
</destination-target>
</firewall-condition>
Under condition, there is a container rate-limit with a leaf
packet-per-second.
Is this a trigger value for the condition, or is it an actual limit
that
the
system is expected to enforce? If it's a trigger, it may be good to
find
a
clearer name. If it's enforced, it's placement under condition is
deceiving.
If a rule's action is set to 'rate-limit', to which rate will it be
limited?
24. Security Considerations
Section 10 in the NSF document under review is the Security
Considerations. I
think it would make sense to mention something about the management
access
control mechanism here, and its relation to NACM.
(End of list)
_______________________________________________
I2nsf mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/i2nsf
