routing-policy: new explicit action and behaviour clarification

[rszarecki]

This PR:

• Adding new option for policy statement action "NEXT_STATEMENT".
• Defining default policy statement action as REJECT, if leaf is omitted in setRequest.
• Clarify behaviour if given route is not explicitly accepted or rejected in
  any of statement of any of policies on the list";

This is (potentially) breaking change due to introduction of defaul value.

Platform Implementations

The are subtele differences among implementations

JUNIPER JUNOS: Actions in Routing Policy Terms

[edit policy-options policy-statement policy-name term term-name]
then {
   accept|reject|next-term;
}

Mapping to this proposal. The * indicate implicit default action.

This proposal	JUNOS
ROUTE_ACCEPT	accept
ROUTE_REJECT*	reject
NEXT_STATEMENT	next-term*

Note: JUNOS support few more flow-controll actions

CISCO IOS-XR: Polixy Statement disposition

Mapping to this proposal. The * indicate implicit default action.

This proposal	IOS-XR RPL
ROUTE_ACCEPT	N/A *
ROUTE_REJECT*	drop*
NEXT_STATEMENT	N/A ("pass" is similar but not exact)

Note:

• IOS-XR do not have explicit equivalent of OpenConfig ROUTE_ACCEPT. If statement is modifying any route attribute, route is implicitly accepted and no further statement are evaluated. If statement do not modify any attribute, route is implicitly dropped.
• IOS-XR "pass" is similar to OpenConfig NEXT_SATEMENT, except it mark route as t"conditionally accepted" if not rejected by subsequent statement.

ARISTA EOS Route Maps

Mapping to this proposal. The * indicate implicit default action.

This proposal	IOS-XR RPL
ROUTE_ACCEPT	permit
ROUTE_REJECT*	deny
NEXT_STATEMENT	continue

Note:
The "permit" or "deny" are mandatory, hence ther is no implicit action. When "continue" also present, action of highes matching statement is applied.

[OpenConfigBot]

Major YANG version changes in commit 13e1882:

[OpenConfigBot]

Compatibility Report for commit 13e1882:
⛔ pyangbind@1b7ee10

[rszarecki]

Subject to discussion. This proposal make REJECT as implicit implicit default action, which is considered safer behaviour.
Alternative would be NEXT_STATEMENT.

I'm seeking for opinions and comments in this area.

[dplore]

Great minds think alike, see #949