Hi Chris and Acee, and everyone,


    I would like to request working group adoption of "Topology-Transparent 
Zone"

(TTZ for short) https://datatracker.ietf.org/doc/draft-chen-isis-ttz/ .


    This draft comprises the following solutions for helping to improve 
scalability:

        1) abstracting a zone to a single pseudo node in IS-IS,

        2) abstracting a zone to a single pseudo node in OSPF,

        3) abstracting a zone to zone edges' full mess in IS-IS, and

        4) transferring smoothly between a zone and a single pseudo node.

    A zone is a block of an area (IS-IS L2 or L1 area, OSPF backbone or

non-backbone area).



    When a network area becomes (too) big, we can reduce its size in the sense

of its LSDB size through abstracting a zone to a single pseudo node or

abstracting a few zones to a few pseudo nodes.



    While a zone is being abstracted (or transferred) to a single pseudo node,

the network is stable. There is no or minimum service interruption.



    After abstracting a few zones to a few pseudo nodes, if we want to 
reconstruct

them, we can transfer (or roll) any of the pseudo nodes back to its zone 
smoothly

with no or minimum service interruption.



    We had a prototype implementation of abstracting a zone to zone edges' full

mess in OSPF. The procedures and related protocol extensions for transferring

smoothly from a zone to zone edges' full mess are implemented and tested.

A zone (block of an OSPF area) is smoothly transferred to its edges’ full mess

without any routing disruptions. The routes on every router are stable while

the zone is being transferred to its edges' mess. It is very easy to operate

the transferring.



    There are two other drafts for improving scalability: "Area Proxy for IS-IS"

(Area Proxy for short) and "IS-IS Flood Reflection" (Flood Reflection for 
short).



    "Area Proxy" https://tools.ietf.org/html/draft-li-lsr-isis-area-proxy-03

abstracts an existing IS-IS L1 area to a single pseudo node.



    "Flood Reflection" 
https://tools.ietf.org/html/draft-przygienda-lsr-flood-reflection-01

abstracts an existing IS-IS L1 area to its edges' connections via one or more

flood reflectors.



    We believe that TTZ has some special advantages even though

Area Proxy and Flood Reflection are very worthy. We would like

to ask for working group adoption of TTZ.



Best Regards,

Huaimo
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