Re: [RTG-DIR] RtgDir Early review: draft-ietf-rtgwg-atn-bgp-12.txt

["Templin (US), Fred L" <[e-mail]>]

Mach, thanks for these clarifications; I am good with everything you said.
One point however is that there may be cases when a c-ASBR has a default
route or a shorter prefix that completely covers a (longer) MSP. I think the
text you offered would be compatible with those cases.

Regards - Fred

> -----Original Message-----
> From: Mach Chen [mailto:[e-mail]]
> Sent: Monday, February 07, 2022 2:01 AM
> To: Templin (US), Fred L <[e-mail]>; Mach Chen <mach.chen=[e-mail]>; rtgwg-chairs <rtgwg-
> [e-mail]>; [e-mail]
> Cc: [e-mail]; [e-mail]
> Subject: [EXTERNAL] RE: RtgDir Early review: draft-ietf-rtgwg-atn-bgp-12.txt
> 
> EXT email: be mindful of links/attachments.
> 
> 
> 
> Hi Fred,
> 
> Some responses inline...
> 
> > -----Original Message-----
> > From: rtg-dir [mailto:[e-mail]] On Behalf Of Templin (US),
> > Fred L
> > Sent: Tuesday, February 1, 2022 1:44 AM
> > To: Mach Chen <mach.chen=[e-mail]>; rtgwg-chairs
> > <[e-mail]>; [e-mail]
> > Cc: [e-mail]; [e-mail]
> > Subject: Re: [RTG-DIR] RtgDir Early review: draft-ietf-rtgwg-atn-bgp-12.txt
> >
> > Mach, thank you very much for this helpful pre-review and see below for
> > follow-up:
> >
> > Fred
> >
> > > -----Original Message-----
> > > From: rtgwg [mailto:[e-mail]] On Behalf Of Mach Chen
> > > Sent: Friday, January 28, 2022 2:07 AM
> > > To: rtgwg-chairs <[e-mail]>;
> > > [e-mail]
> > > Cc: [e-mail]; [e-mail]
> > > Subject: RtgDir Early review: draft-ietf-rtgwg-atn-bgp-12.txt
> > >
> > > Hello
> > >
> > > I have been selected to do a routing directorate “early” review of this
> > draft.
> > > ​https://datatracker.ietf.org/doc/ draft-ietf-rtgwg-atn-bgp-12/
> > >
> > > The routing directorate will, on request from the working group chair,
> > > perform an “early” review of a draft before it is submitted for
> > > publication to the IESG. The early review can be performed at any time
> > during the draft’s lifetime as a working group document. The purpose of the
> > early review depends on the stage that the document has reached.
> > >
> > > As this document is going to be in working group last call, my focus
> > > for the review was to determine whether the document is ready to be
> > published. Please consider my comments along with the other working group
> > last call comments.
> > >
> > > For more information about the Routing Directorate, please see
> > > ​http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir
> > >
> > > Document: draft-ietf-rtgwg-atn-bgp-12.txt
> > > Reviewer: Mach Chen
> > > Review Date: 2022/1/28
> > > Intended Status: Informational
> > >
> > > Summary:
> > >
> > > This document is basically ready for publication, but has nits that should be
> > considered prior to being submitted to the IESG..
> > >
> > > Comments:
> > >
> > > 1. Section 2,
> > >  "OAL Autonomous System", no places in this document refer to the term,
> > if there is no use, it should be removed..
> > >
> > > 2. Section 2,
> > > Core Autonomous System
> > >       The "hub" autonomous system maintained by all c-ASBRs within
> > the
> > >       same partition.
> > > I have difficult to understand the above definition, need some
> > > clarification text if the term is desired. BTW, I found that this term
> > > is only used for definition of "OAL Autonomous System", given that "OAL
> > Autonomous System" is not used in the document, the simplest solution is
> > to remove this term as well.
> >
> > The terms "OAL AS", "Core AS" and "Stub AS" are used throughout the
> > document and are needed to set the proper context. Would it help if I were
> > to add the abbreviations (OAL AS, Core AS and Stub AS) to the respective "*
> > Autonomous System" definitions?
> 
> Yes, indeed.
> 
> >
> > > 3. Section 3,
> > > "...The overlay does not
> > >    interact with the underlying INET BGP routing systems, and only a
> > >    small and unchanging set of MSPs are advertised externally instead of
> > >    the full dynamically changing set of MNPs."
> > >
> > > The front part says that there is no interaction with the underlying
> > > INET BGP routing system, the second half say there may be some MSPs
> > advertised between the two, seems it's self-contradictory?
> >
> > How does this sound for a rewrite:
> >
> > "...The ATN/IPS routing system interacts with underlying INET BGP routing
> > systems only through the static advertisement of a small and unchanging set
> > of MSPs instead of the full dynamically changing set of MNPs."
> 
> Looks good to me.
> 
> >
> > > 4. Section 3,
> > > s/each s-ASBRs/each s-ASBR
> >
> > Agreed.
> >
> > > 5. Section 3,
> > > "Since the BGP instance does not
> > >    connect with any INET BGP routing systems, the ASNs assigned need
> > not
> > >    be coordinated with IANA and can in fact coincide with values that
> > >    are assigned in other domains.  The only requirement is that ASNs
> > >    must not be duplicated within the ATN/IPS routing system itself."
> > > Why not just use the private ASNs? It will avoid potential conflicts with the
> > Internet ASNs.
> >
> > Indeed. When this text was written, I was working under the limiting
> > assumption that only 1023 16-bit AS numbers were reserved for private use
> > which is far fewer than may be needed in some large deployments.
> > But, I did not know about RFC6996 which reserves 94,967,295 32-bit AS
> > numbers for private use which would seem to satisfy most deployments.
> > So, the proposed resolution is to cite RFC6996 and recommend (but not
> > mandate) private use 32-bit AS numbers. The reason to "not mandate"
> > is that enormous deployments could theoretically exhaust even the 32-bit
> > private AS number space.
> 
> OK.
> 
> >
> > > 6. Section 3, para 5,
> > > "Each c-ASBR configures a black-hole route for each of its MSPs.  By
> > >    black-holing the MSPs, the c-ASBR will maintain forwarding table
> > >    entries only for the MNP-ULAs that are currently active, and packets
> > >    destined to all other MNP-ULAs will correctly incur ICMPv6
> > >    Destination Unreachable messages [RFC4443] due to the black hole
> > >    route."
> > > In my understanding, the black-hole route will cause the packets
> > > (without matching a specific MNP-ULA) to be dropped silently, and no
> > > ICMPv6 Destination Unreachable message will be incurred. Seems that the
> > black-hole route does not satisfy your requirement.
> >
> > This may require a bit more explanation. The requirement is for a c-ASBR that
> > lacks a MNP  route matching a packet's destination address to drop the
> > packet and return an ICMPv6 Destination Unreachable. However, if there
> > were no black-hole MSP route, the packet could escape from the domain via
> > a less-specific route (e.g., "default") where it might be again injected back
> > into the overlay routing system and kicked back out by a default route ad
> > infinitum. So, black-holing the MSPs seems to be necessary, but how to make
> > the behavior of "drop and send ICMP"
> > based on matching the MSP is the question. Any suggestions?
> 
> Unless there are some scenarios that require the c-ASBR to install a default. In my understanding, the c-ASBR does not have to maintain any
> default route, only the s-ASBR does. With this, the c-ASBR will drop the packet without matching a MNP and an ICMPv6 Destination
> Unreachable will be generated accordingly.
> 
> Or maybe:
> "Each c-ASBR configures a black-hole route for each of its MSPs.  By
>     black-holing the MSPs, the c-ASBR will maintain forwarding table
>     entries only for the MNP-ULAs that are currently active, and packets
>     destined to all other MNP-ULAs will silently be dropped due to the black hole route, and a corresponding log will be recorded for this
> event."
> >
> > > 6. Section 4, para 6
> > > "The s-ASBR's stub AS therefore
> > >    consists of the set of all of its active Clients (i.e., the stub AS
> > >    is a logical construct and not a physical construct)."
> > > From the BGP point of view, an AS is consisted of the routers that are
> > > running BGP protocol, the Clients are actually outside the AS and not
> > belong to the AS, unless the Clients or Proxy servers peer with the s-ASBR.
> >
> > OK, thanks for this. How does this look for a rewrite:
> >
> > "The s-ASBR's stub AS is therefore used only to advertise the set of MNPs of
> > all its active Clients and not to peer with other BGP routers (i.e., the stub AS
> > is a logical construct and not a physical one)."
> 
> Maybe this?
> "The s-ASBR's stub AS is therefore used only to advertise the set of MNPs of
> all its active Clients and not to peer with other BGP routers, the stub AS is a logical construct and not a physical one."
> 
> >
> > > 7. Section 5,
> > > In Figure 4/5, is the P/S a s-ASBR? If so, it's better to add some
> > > text to make it clearer. If not, how does P/S-1 know a packet should be sent
> > directly to P/S-2 instead to s-ASBR1?
> >
> > Yes, all P/S's are also s-ASBRs and serve a subset of the Clients in the system.
> > However, each Client 'A' that uses P/S 'B' as its s-ASBR could also have links
> > that connect through P/S's 'C', 'D', 'E', etc. Then, from the perspective of 'A',
> > only 'B' is the s-ASBR and all others are simple P/S's which coordinate with
> > the s-ASBR on 'A's behalf.
> >
> > The name "Proxy/Server" is intentionally chosen to show this duality of
> > function - the "P/S" in some instances acts as a simple Proxy and in other
> > instances acts as a Server (i.e., as a s-ASBR).
> >
> > I will see if I can add some text throughout the document that would make
> > this point clearer.
> 
> Great!
> 
> Best regards,
> Mach
> >
> > > Best regards,
> > > Mach
> > > _______________________________________________
> > > rtgwg mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/rtgwg