Re: [Idr] The automatic policy exchange by draft-ietf-idr-rpd-05.txt can be used for draft-ietf-rtgwg-net2cloud-gap-analysis

Robert Raszuk <robert@raszuk.net> Sun, 26 July 2020 22:23 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Mon, 27 Jul 2020 00:22:59 +0200
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To: Linda Dunbar <linda.dunbar@futurewei.com>
Cc: Lizhenbin <lizhenbin@huawei.com>, "Jakob Heitz (jheitz)" <jheitz@cisco.com>, "idr@ietf.org" <idr@ietf.org>, "grow@ietf.org grow@ietf.org" <grow@ietf.org>, "rtgwg@ietf.org" <rtgwg@ietf.org>
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Subject: Re: [Idr] The automatic policy exchange by draft-ietf-idr-rpd-05.txt can be used for draft-ietf-rtgwg-net2cloud-gap-analysis
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Hi Linda,

So are you suggesting that this new SAFI is to be sent on EBGP too ?? Whow
... Note BGP is not too secure transport ! I would never allow any peer to
push me policy via eBGP to my ASBRs regardless how much I would trust it.

That aside I think no one is questioning that overall this is nice to have
BGP policy distributed in a dynamic way. We are however concerned in
three planes ...

Aspect #1 - BGP is p2mp and information and encoding (NLRI) here clearly
make this proposal p2p. And no Robin p2p is not a special case of p2mp :)

Aspect #2 - This proposal adds additional burden to IP Routing BGP
subsystem and its clear that if approved there will be more and more
extensions to new MATCH and SET sub-TLVs coming. While it is easy to write
a draft that at the end requires a serious commitment from any vendor to
now turn BGP into configuration channel. That means overall more cycles
spend and more burden on BGP dev teams.

Aspect #3 - The proposal has lots of technical issues (as described) which
can not just be swapped under the carpet.

My recommendations (in order of preference):

*1*

Turn proposed sub-TLVs into JSON and use HTTPS PUT, GET & DELETE along with
real time response status codes to send required policy over targeted TCP
sessions just using curl to remote ASBRs. Note all vendors today support
RESTful commands or httpd on the routers. Some already even support JSON
based BGP configuration for some time now (ex: NX-OS).

*2*

At least decouple it from routing BGP - support new BGP Transport Instance
with new separate port and separate process. Whenever we need to use such
protocol (call it Configuration Transport Protocol "CTP") for loop free
information dissemination such isolation could deliver what you are really
after with no impact to stability of IP routing.
Ref: https://tools.ietf.org/html/draft-raszuk-ti-bgp-01

Thx,
R.


On Sun, Jul 26, 2020 at 11:53 PM Linda Dunbar <linda.dunbar@futurewei.com>
wrote:

> Robert, Jakob, etc.
>
> Thank you very much for detailed explanation of the issues.
> One of the points you all raised is that p2p policies should be
> administrated by controller via NETCONF.
>
> *https://datatracker.ietf.org/doc/draft-ietf-rtgwg-net2cloud-gap-analysis/*
> <https://datatracker.ietf.org/doc/draft-ietf-rtgwg-net2cloud-gap-analysis/>
> describes a scenario of one vCPE in cloud DC reachable by multiple PEs. Depending
> on the nature of the applications or/and network conditions, some
> applications may need to egress or ingress from PE1, others may need to
> egress or ingress from PE2.
>
> Today’s Cloud DC configuration can use the AS Path metric to influence the
> preferred path to/from a specific PEs. But requires manual configuration.
> After reading through the draft-ietf-idr-rpd-05, I think the automatic
> approach can make the change on demand. The policy change can be ephemeral.
> Therefore, if one side doesn’t implement the feature, the “spray” doesn’t
> have any impact. The traffic egress or ingress to the peer network would
> just go with the configuration. If the “spray” is answered, then the
> performance can be improved.
>
>
>
>
>
>
> If not using the automatic method proposed by draft-ietf-idr-rpd, do you
> have other suggestions?
>
> Thank you very much.
>
> Linda Dunbar
> *From:* Robert Raszuk <robert@raszuk.net>
> *Sent:* Friday, July 24, 2020 2:50 PM
> *To:* Linda Dunbar <linda.dunbar@futurewei.com>om>; Lizhenbin <
> lizhenbin@huawei.com>
> *Cc:* Jakob Heitz (jheitz) <jheitz@cisco.com>om>; idr@ietf.org; grow@ietf.org
> grow@ietf.org <grow@ietf.org>
> *Subject:* Re: [Idr] WG LC on draft-ietf-idr-rpd-05.txt (7/15 to
> 7/29/2020)
>
> Linda,
>
> It seems that authors of this document are strongly pushing to pass the
> last call irrespective of observations made by WG.
>
> As said before and as reiterated by Jakob and Ketan BGP is not the right
> tool for p2p config push. We must stop adding such extensions to BGP like
> this one or BGP-LS or SR Policies if we really want to keep routing at some
> proper stability levels.
>
> But even if you would convince everyone in IDR that this is all great the
> draft itself is so immature that I can't imagine why are we discussing last
> call at this time.
>
> * Please observe that BGP state is ephemeral. When BGP sessions resets all
> state previously distributed is gone (modulo GR ...) Is the
> expectation here that state distributed by this new SAFI will persists ? If
> so for how long ? If not have you even considered the initial churn ?
>
> * We have hooks to make sure LDP and IGP play in concert with BGP
> reachability. Would we need to now add to also wait for BGP policy to be
> received from controllers ?
>
> * We have spent fair amount of time to make sure GR works well. Do you
> expect to now GR to recognize all policy parameters and sync deltas locally
> upon BGP sessions restarts ?
>
> * Do you expect BGP implementations to now get busy with understanding all
> BGP policies syntax and semantics not in current terms how they are send or
> received in BGP UPDATEs but how they are applied implementation by
> implementation ...
>
> * What happens when some implementation does not allow some policy defined
> in the draft ... for example flexible AS_PATH creation as defined in
> AS-Path Change sub-TLV ? Note that this section alone is catastrophic for
> BGP protocol to allow insertion of more then your own ASN into AS-PATH.
> Just looking at this alone should be enough to reject this draft.
>
> And there are many many more real issues with this proposal  ....
>
> See when document has low adoption bar it does not mean that it will also
> have the same low bar to progress it :)
>
> Kind regards,
> R.
>
> PS. Let me cc GROW WG here as I think more operational review and comments
> would be highly valuable at this point.
>
>
>
> On Fri, Jul 24, 2020 at 6:28 PM Linda Dunbar <*linda.dunbar@futurewei.com*
> <linda.dunbar@futurewei.com>> wrote:
> Jakob,
>
> Comparing Netconf with BGP  is not apple to apple comparison.
> I remember a few years ago that  Netconf advocators have claimed that
> Netconf can replace PCE, replace BGP, replace xx, …
>
> After many years debate,  many of the Netconf  limitations have been
> acknowledged,  that is why PCE still exists, so does BGP.
>
> Other comments are inserted below:
>
> *From:* Jakob Heitz (jheitz) <*jheitz@cisco.com* <jheitz@cisco.com>>
> *Sent:* Thursday, July 23, 2020 5:37 PM
> *To:* Linda Dunbar <*linda.dunbar@futurewei.com*
> <linda.dunbar@futurewei.com>>m>>; *idr@ietf.org* <idr@ietf.org>
> *Subject:* RE: WG LC on draft-ietf-idr-rpd-05.txt (7/15 to 7/29/2020)
>
> Netconf provides needed features that BGP does not have:
> - Atomic Transactions:
>   If one configuration item fails, they all fail.
>   They all either succeed or all fail. There is no partial success.
>   Multiple configurations in one transaction are applied at the same time.
>    . This avoids non-deterministic transient behavior between application
> of the first policy and the last.
> [Linda] Just like Routes Advertisement, receivers can improperly install
> the routes into their RIB/FIB.  BGP has been running for over 3 decades.
> Those who don’t implement correctly eventually fix their bugs.
>  If the Policies sent to peers are not enforced  as the RPD is asking for,
>  traffic might be sent to non-preferred links, just like a BGP receiver
> incorrectly processes the BGP route updates.
>
> - Feedback:
>   BGP is "spray and pray".
>   Netconf provides an acknowledgement that the config either failed or was
> applied,
>   which then allows the controller to take the next steps with
>   reliable information about what configuration exists in the network.
>
> [Linda]  BGP UPDATE is over reliable TCP transport and BGP protocol itself
> can guarantee the proper distribution of the UDPATE. Therefore, its “spray
> and pray” nature has its advantage of optimized processing. BGP  Route
> Update doesn’t expect confirmation from  the receivers.
>
> - Persistence:
>   If the BGP session were to go down, all the configuration it sent will
> be implicitly withdrawn.
>
> If another AS would not allow a foreign AS to configure it with netconf,
> it would not allow it with RPD either.
> [Linda] That is very true. The originator can only “Pray” as BGP is
> intended for.
>
> There are already ways in BGP for an AS to signal preference across AS
> boundaries:
> Med, AS-path length, communities.
>
> [Linda] All those methods you have mentioned require heavy duty
> configurations, which is difficult to change on the fly. The proposed
> method is a flexible method which allows policies to be changed on the fly
> (depending on real time traffic conditions).
>
>
> Ketan and Robert added other objections.
> [Linda] I have been studying their reasons for the objections.
>
> Thank you very much for the explanation.
>
> Linda Dunbar
>
>
> Regards,
> Jakob.
>
> *From:* Linda Dunbar <*linda.dunbar@futurewei.com*
> <linda.dunbar@futurewei.com>>
> *Sent:* Thursday, July 23, 2020 3:24 PM
> *To:* Jakob Heitz (jheitz) <*jheitz@cisco.com* <jheitz@cisco.com>>m>>;
> *idr@ietf.org* <idr@ietf.org>
> *Subject:* RE: WG LC on draft-ietf-idr-rpd-05.txt (7/15 to 7/29/2020)
>
> Jakob,
>
> Can you elaborate those automation configuration methods that are much
> better and less error prone than the proposed one?
> It will take a long time to dig through so many IDR emails to find them.
>
> Thank you very much,
> Linda Dunbar
>
> *From:* Jakob Heitz (jheitz) <*jheitz@cisco.com* <jheitz@cisco.com>>
> *Sent:* Thursday, July 23, 2020 5:20 PM
> *To:* Linda Dunbar <*linda.dunbar@futurewei.com*
> <linda.dunbar@futurewei.com>>m>>; *idr@ietf.org* <idr@ietf.org>
> *Subject:* RE: WG LC on draft-ietf-idr-rpd-05.txt (7/15 to 7/29/2020)
>
> Of course it's better than manual configuration.
> That's not much of an argument, because there are plenty of
> automatic configuration methods that are much better and
> less error prone than this draft as I and others have pointed
> out in previous emails.
>
> Regards,
> Jakob.
>
> *From:* Idr <*idr-bounces@ietf.org* <idr-bounces@ietf.org>> *On Behalf Of
> *Linda Dunbar
> *Sent:* Thursday, July 23, 2020 2:57 PM
> *To:* *idr@ietf.org* <idr@ietf.org>
> *Subject:* Re: [Idr] WG LC on draft-ietf-idr-rpd-05.txt (7/15 to
> 7/29/2020)
>
> I support the WGLC for the draft. I think the proposed distribution of
> policy can scale much better and less error prone than any manual
> configuration.
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