Re: [netmod] WG Last Call: draft-ietf-netmod-acl-model-14

Kristian Larsson <kristian@spritelink.net> Thu, 02 November 2017 07:43 UTC

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Date: Thu, 2 Nov 2017 08:43:18 +0100
From: Kristian Larsson <kristian@spritelink.net>
To: Mahesh Jethanandani <mjethanandani@gmail.com>
Cc: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>, "netmod@ietf.org" <netmod@ietf.org>
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Subject: Re: [netmod] WG Last Call: draft-ietf-netmod-acl-model-14
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On Thu, Nov 02, 2017 at 06:13:04AM +0630, Mahesh Jethanandani wrote:
>     On Nov 1, 2017, at 5:52 PM, Juergen Schoenwaelder <
>     j.schoenwaelder@jacobs-university.de>; wrote:
> 
>     Mahesh,
> 
>     I think the question is why we need to have different match containers
>     for each possible feature set combination instead of having a single
>     match container with groups of leafs in it marked as features. This
>     would seem to cut down the size of the module and the tree diagram
>     significantly. I think this will also make clients simpler sicne they
>     do not have to select a certain container based on the feature set
>     announced. 
> 
> 
> The current design of match containers was chosen to allow platforms to select
> one container that matched what the hardware supported from a l2, l3 and ipv
> {4,6} perspective.

Sure, but you are conflating the structure of the model with the
feature-wraps. Without changing the features of the model, we can
structure it in a different way where there is not a 1:1 mapping
between features and containers under the matches container.


> I would argue that even though the overall diagram is bigger
> with this design, once the platform selects the container of choice, the tree
> and the configuration itself would be a little simpler/smaller. 

I am arguing the opposite. It's really awkward to place the same
type of data, like IPv4 match conditions, under different paths
based on a feature.

If the system model had done the same we would have:
/system
/system-with-ntp
/system-with-ntp-and-radius

How do you augment in new leaves? While you are using groupings
which allows for a reuse of data across all these containers,
someone who is augmenting can't, since you can't augment a
container, only where it is used. Someone wishing to add a leaf
to the model needs to augment in three different locations to
support a new match condition for IPv4 (let's say some meta-data
attribute).


> Take the case where the desired selection is l2,-l3, ipv4 and ipv6. The current
> tree looks like this:
> 
> 
>         |        |  +--rw l2-l3-ipv4-ipv6-acl {l2-l3-ipv4-ipv6-acl}?
>         |        |  |  +--rw destination-mac-address?        yang:mac-address
>         |        |  |  +--rw destination-mac-address-mask?   yang:mac-address
>         |        |  |  +--rw source-mac-address?             yang:mac-address
>         |        |  |  +--rw source-mac-address-mask?        yang:mac-address
>         |        |  |  +--rw ethertype?                      eth:ethertype
>         |        |  |  +--rw dscp?                           inet:dscp
>         |        |  |  +--rw ecn?                            uint8
>         |        |  |  +--rw length?                         uint16
>         |        |  |  +--rw ttl?                            uint8
>         |        |  |  +--rw protocol?                       uint8
>         |        |  |  +--rw source-port-range!
>         |        |  |  |  +--rw lower-port    inet:port-number
>         |        |  |  |  +--rw upper-port?   inet:port-number
>         |        |  |  |  +--rw operation?    operator
>         |        |  |  +--rw destination-port-range!
>         |        |  |  |  +--rw lower-port    inet:port-number
>         |        |  |  |  +--rw upper-port?   inet:port-number
>         |        |  |  |  +--rw operations?   operator
>         |        |  |  +--rw ihl?                            uint8
>         |        |  |  +--rw flags?                          bits
>         |        |  |  +--rw offset?                         uint16
>         |        |  |  +--rw identification?                 uint16
>         |        |  |  +--rw destination-ipv4-network?       inet:ipv4-prefix
>         |        |  |  +--rw source-ipv4-network?            inet:ipv4-prefix
>         |        |  |  +--rw next-header?                    uint8
>         |        |  |  +--rw destination-ipv6-network?       inet:ipv6-prefix
>         |        |  |  +--rw source-ipv6-network?            inet:ipv6-prefix
> 
>         |        |  |  +--rw flow-label?
>         |        |  |          inet:ipv6-flow-label
> 
> 
> 
> whereas, if the design went with one match container with each group of leafs
> in their own container (to support the if-feature statement for that
> container), the tree would look like this:
> 
> 
>         |        |  +--rw l2-acl {l2-acl}?
>         |        |  |  +--rw destination-mac-address?        yang:mac-address
>         |        |  |  +--rw destination-mac-address-mask?   yang:mac-address
>         |        |  |  +--rw source-mac-address?             yang:mac-address
>         |        |  |  +--rw source-mac-address-mask?        yang:mac-address
>         |        |  |  +--rw ethertype?                      eth:ethertype
> 
>         |        |  +--rw ipv4-acl {ipv4-acl}?
>         |        |  |  +--rw dscp?                       inet:dscp
>         |        |  |  +--rw ecn?                        uint8
>         |        |  |  +--rw length?                     uint16
>         |        |  |  +--rw ttl?                        uint8
>         |        |  |  +--rw protocol?                   uint8
>         |        |  |  +--rw source-port-range!
>         |        |  |  |  +--rw lower-port    inet:port-number
>         |        |  |  |  +--rw upper-port?   inet:port-number
>         |        |  |  |  +--rw operation?    operator
>         |        |  |  +--rw destination-port-range!
>         |        |  |  |  +--rw lower-port    inet:port-number
>         |        |  |  |  +--rw upper-port?   inet:port-number
>         |        |  |  |  +--rw operations?   operator
>         |        |  |  +--rw ihl?                        uint8
>         |        |  |  +--rw flags?                      bits
>         |        |  |  +--rw offset?                     uint16
>         |        |  |  +--rw identification?             uint16
>         |        |  |  +--rw destination-ipv4-network?   inet:ipv4-prefix
>         |        |  |  +--rw source-ipv4-network?        inet:ipv4-prefix
>         |        |  +--rw ipv6-acl {ipv6-acl}?
>         |        |  |  +--rw dscp?                       inet:dscp
>         |        |  |  +--rw ecn?                        uint8
>         |        |  |  +--rw length?                     uint16
>         |        |  |  +--rw ttl?                        uint8
>         |        |  |  +--rw protocol?                   uint8
>         |        |  |  +--rw source-port-range!
>         |        |  |  |  +--rw lower-port    inet:port-number
>         |        |  |  |  +--rw upper-port?   inet:port-number
>         |        |  |  |  +--rw operation?    operator
>         |        |  |  +--rw destination-port-range!
>         |        |  |  |  +--rw lower-port    inet:port-number
>         |        |  |  |  +--rw upper-port?   inet:port-number
>         |        |  |  |  +--rw operations?   operator
>         |        |  |  +--rw next-header?                uint8
>         |        |  |  +--rw destination-ipv6-network?   inet:ipv6-prefix
>         |        |  |  +--rw source-ipv6-network?        inet:ipv6-prefix
>         |        |  |  +--rw flow-label?                 inet:ipv6-flow-label
> 
> 
> The difference though is small and comes down to a preference. Select one
> feature statement and get one container with everything in it, or define
> multiple feature statements and assemble together the pieces to define the ACE
> entry.

Again, I think you mix up the features available vs the structure
of the data.

This is the current list of features (which again, I want to
change but that's separate):
 * l2-acl
 * ipv4-acl
 * ipv6-acl
 * mixed-ipv4-acl
 * mixed-ipv6-acl
 * l2-l3-ipv4-ipv6-acl
 * tcp-acl
 * udp-acl
 * icmp-acl
 * any-acl

As per your second example above we have an ipv4-acl container
under matches, i.e. /access-list/acl/aces/ace/matches/ipv4-acl.
It is only possible to define ipv4 matches if one of the
following features are present:
 * ipv4-acl
 * mixed-ipv4-acl
 * l2-l3-ipv4-ipv6-acl

Thus you write an if-feature statement to reflect that, like
this:

 if-feature "ipv4-acl mixed-ipv4-acl l2-l3-ipv4-ipv6-acl";

So you see, the tight coupling you have between the data
structure and the if-features isn't necessary.

I think the structure should first be established without
features and then features can be inserted where they make sense
to make part of the model optional. Starting with the list of
features and then designing the structure around them makes for a
much less natural data structure IMHO.

Kind regards,
   Kristian.