1. Synchronisation of Network Parameters draft-bryant-rtgwg-param-sync-00
S. Bryant: Huawei Technologies
A. Atlas & C. Bowers: Juniper Networks
RTGWG IETF97

2. Genesis
Once upon a time there was draft-atlas-bryant-shand-lf-timers (Synchronisation of Loop Free Timer Values). This was intended to synchronize the value of timers for loop free convergence. It died of neglect.
The MRT drafts needed flooding-domain-wide common convergence timer and embedded it into the protocol.
The authors of both drafts thought that there was a case for pulling this out of MRT to make the timer available for other applications.
The authors realized that there are other potentially other flooding- domain-wide parameters and it was very simple to generalize the mechanism to support other applications.

3. The Alternative
Bake the constant into the protocol – Would not work in this case because the parameter is h/w, configuration and n/w dependent
Static/Manual Configuration – Error prone and in practice difficult (impossible) to change in a practical network.
An SDN approach, but not all networks are SDN controlled.
Getting a node to flood its preferred parameter value and using a well known method to agree one what is to be used avoids these problems.

4. Overview Each node floods its preferred parameter value
Each node supporting the parameter knows the selection algorithm (e.g. largest, smallest, some other criteria)
Each node runs the algorithm and calculates the parameter value
There is no negotiation. It is just like the routing protocol itself, a node receives the link state information, calculates what to do, does it and trusts that all the other nodes will do likewise.

5. A New Parameter Value
Is used as soon as it is received, but a change in value does not prompt any action unless that is a characteristic of the parameter.
In the case of convergence timers, a new convergence value is not used until the next convergence event.

6. ISIS TYPE: <TBD> Length: As defined by parameter definition.
Network Wide Parameter (NWP) sub-TLV added to the IS-IS Router CAPABILITY TLV (TLV #242
Setting of the S-bit in TLV #242 (Inter-level leaking) MUST is part of the parameter definition
Network Wide Parameter Sub-TLV
TYPE: <TBD>
Length: As defined by parameter definition.
Sub-sub-TLV
NWP Type: (16 bits) as defined in NWP Registry
NWP Value: As defined by parameter definition

7. OSPF New OSPF Router Information LSA TLV is defined.
Carried in a type 10 or type 11 OSPF Opaque LSA depending flooding scope.
Network Wide Parameter TLV
TYPE: <TBD>
Length: As defined by parameter definition.
Sub-TLV
NWP Type: (16 bits) as defined in NWP Registry
NWP Value: As defined by parameter definition

8. Required Properties
Convergence delay MUST be consistent among all routers.
Convergence delay MUST be the highest value advertised by any router in the new topology.
MUST increase the delay when a new router in introduced that requires a higher delay
When router with longest delay is removed next longest delay is used.
A router can change the convergence delay timer value that it requires.
A router in multiple areas, or is running multiple routing protocols MAY signal a different value in each case.
How the time to converge is determined is outside the scope of this specification.

9. Definition of the Convergence Timer
The NWP value is 16 bits (ms)milliseconds; maximum value ~65s.
The NWP is largest value advertised.
If Convergence Timer value, but not topology changes the new value considered time but transition not initiated.
If Convergence Timer value and the topology changes, a transition starts and the new timer value considered.
RTG protocol specifies action when both parameters change during during the hold-off time.
All routers supporting controlled convergence MUST advertise Convergence Time.
In ISIS the S-bit=0, then Convergence Timer NWP MUST NOT be leaked between levels.
If the parameter is carried in OSPF it is only carried in a type 10 Opaque LSA which prevents propagation outside the OSPF area.

10. Next Steps
The MRT project needs this parameter distribution system to compete its design.
There is merit in providing the general solution rather than employing a point solution.
The authors request that this be adopted as a WG draft so that design authority passes to the RTGWG.
The authors request that the chairs progress this draft in a timely way so as not to stall the MRT project.