Re: [Idr] draft-wang-idr-vpn-routes-control-analysis (was Re: rd-orf problem clarification at the local level)

[Gyan Mishra <[e-mail]>]

Hi Robert

In the first comment in the thread as a requirement to identify the
Prefixes based on RD to be blocked in the case of not unique RD requires an
AND of both RD+RT in the logic.  I am in complete agreement that is
required.

So I can see Jeffrey’s idea as a possible solution to modify RTC to include
offending RD update to RTC spec.

However, the RD ORF uses existing ORF machinery with add of new ORF type
which to me seems a very minor change.  The nice thing about RD ORF is that
it is controlled and requires manual intervention to unblock where RTC
would be automatic and that could cause undesirable instability.

I am not sure if modifying RTC to include RD block logic would not cause
added instability with RTC as RTC acts only on RT, as I this is a
significant change to RTC membership logic.  Also any existing
implementation of RTC would all be impacted by this change.  With RD ORF as
this is a new type ORF, the ORF policy would have to be explicitly defined
so this would only effect new deployments wanting to take advantage of RD
ORF granularity of filtering.


Gyan

On Fri, Feb 26, 2021 at 5:47 AM Robert Raszuk <[e-mail]> wrote:

> Gyan,
>
> What you said is pretty obvious I think to everyone here.
>
> But I think the point of bringing RTC into this picture was a bit
> different.
>
> Just imagine RTC is running between PE and RR and signals interest in set
> of RTs to the RR. Let's say those RTs are RT100, RT200, RT300, RT400, RT500
>
> Further imagine one VRF importing RT200 overflows on said PE with incoming
> (pre-import routes of RD_FOO and RT100, RT200 and RT 300).
>
> So what if now PE via RTC will simply readvertise interest to get RT200
> with new BGP attribute say called BLOCK_RD and lists in such attribute body
> Route Distinguisher of RD_FOO ?
>
> The overall mission accomplished. No need for any new ORF type. It can be
> even transitive if we apply a little hack and adjust the way RR will select
> the best path for RTC (meaning include this attribute in advertisements
> only if all peers sending RT200 attached it with such RD_FOO).
>
> To me this is very simply RTC extension and it seems solves this entire
> "problem".
>
> And no - by proposing the above I am not changing my mind that it is
> simply wrong network operation to even allow such problem to happen in the
> first place.
>
> Best,
> R.
>
>
> On Fri, Feb 26, 2021 at 4:52 AM Gyan Mishra <[e-mail]> wrote:
>
>>
>> Hi Jeff
>>
>> Keep in mind that RTC is an optimization that does not apply to every
>> scenario especially in cases where all PEs have all the same VPNs defined
>> with explicit RT import.  The special cases were RTC does apply is for
>> incongruent VRFs in cases of a sparse RT distribution graph where PEs don’t
>> all import the same RTs.  By default all PE have RT filtering enabled by
>> default meaning if their is not an explicit VRF definition to match and
>> import the RT, the RT is dropped.  With RTC the distribution graph of what
>> RTs are advertised RR-PE is now optimized with RT membership, and now  only
>> RTs explicitly imported by the PEs are now advertised by the RR to PE for
>> processing.  In the case of RD-ORF, it provides a layer of needed
>> granularity as the RD PE originator of the flood is a subset of all the VPN
>> prefixes represented by the RT permitted by RTC to be advertised to the
>> PE.  The RD-ORF now dynamically blocks the offending PE prefixes that would
>> otherwise have been advertised by RTC RR to PE and accepted by the PE for
>> processing and added to the VRF RIB being overloaded.
>>
>>
>> Kind Regards
>>
>> Gyan
>>
>> On Thu, Feb 25, 2021 at 6:21 PM Aijun Wang <[e-mail]>
>> wrote:
>>
>>> Hi, Jeff:
>>> Thanks for your suggestions!
>>> I think combine RTC and RD-ORF information can accomplish the fine
>>> control for the upstream propagation of unwanted VPN routes.
>>> We will also try to find other ways to achieve the same effect.
>>>
>>> Aijun Wang
>>> China Telecom
>>>
>>> > On Feb 25, 2021, at 22:01, Jeffrey Haas <[e-mail]> wrote:
>>> >
>>> > Aijun,
>>> >
>>> > On Thu, Feb 25, 2021 at 12:07:49PM +0800, Aijun Wang wrote:
>>> >>> In the prior discussions, it was clear that remediation was trying
>>> to be
>>> >>> done on a per-RD basis.  The text in this draft seems to be a larger
>>> scope
>>> >>> than that; perhaps per VPN (and thus route-target?).  Is that your
>>> >>> intention?
>>> >> [WAJ] Yes. We are considering to add RT information to the current
>>> RD-ORF
>>> >> semantic, to identify/control the "excessive routes" in more
>>> granular.
>>> >
>>> > Thanks for the clarification.  That expands the scope of the original
>>> > discussion, but might be helpful for the solution.
>>> >
>>> >>> For a route reflector, it would require that all possible receivers
>>> for a
>>> >>> RD/RT have no interest in the routes, and that the source of the
>>> routes is
>>> >>> clearly directional.  BGP does not provide such a distribution graph.
>>> >>
>>> >> [WAJ] " all its downstream BGP peers can't or don't want to process
>>> it"
>>> >> means RR receives the RD-ORF messages for the same set of VPN routes
>>> from
>>> >> all of its clients. This can be achieved by RR
>>> >
>>> > For my point, consider a trivial case:
>>> >
>>> > PE1 --- RR --- PE2
>>> >
>>> > PE2 is the source of the excess routes.
>>> > PE1 is the impacted router.
>>> > RR has only PE1 and PE2 as peers.
>>> >
>>> > By your current text, RR can only do something if PE1 and PE2 say
>>> they're
>>> > not interested.
>>> >
>>> > It can be observed here that if we have exactly one peer left, we could
>>> > signal to that one peer.
>>> >
>>> > I suspect your intent is to cover situations where you can distinguish
>>> PE
>>> > routers from solely internal route distributuion infrastructure, such
>>> as
>>> > route reflectors.  So, using a slighly more interesting topology:
>>> >
>>> > PE1 --- RR1 --- RR2 --- PE2
>>> >
>>> > PE2 is the source of the excess routes.
>>> > PE1 is the impacted router.
>>> > RR1 has only PE1 as a PE device.
>>> >
>>> > If PE1 signals to RR1 that it isn't interested in the offending
>>> routes, RR1
>>> > may propagate the filter.
>>> >
>>> > The issue here is that BGP does not specifically distinguish whether an
>>> > attached BGP Speaker is a PE or not.  The protocol doesn't help you
>>> make
>>> > this determination.
>>> >
>>> >>> In a network using RT-Constrain without a default RT-Constrain
>>> route, such a
>>> >>> graph potentially exists.
>>> >> [WAJ] RT-Constrain can only express explicitly "what I want" and the
>>> >> distributed graph. It can't express explicitly "what I don't want"
>>> now, also
>>> >> the distribution-block graph. Is that right?
>>> >
>>> > That is correct.  But consider the following example:
>>> >
>>> >        PE3
>>> >         |
>>> > PE1 --- RR1 --- RR2 --- PE2
>>> >
>>> > PE2 is the source of the excess routes for VPN RT-A.
>>> > PE1 is the impacted router.
>>> > RR1 has PE1 and PE3 as attached PE routers.
>>> > All routers are configured to use RT-Constrain
>>> > PE1 and PE2 source RT-Constrain routes for RT-A.  PE3 does not.
>>> >
>>> > If PE1 signals to RR1 that it isn't interested in the offending
>>> routes, and
>>> > that signal not only includes the offending RD, but also the matching
>>> RTs,
>>> > RR1 can determine that there are no further interested receivers for
>>> that
>>> > RD+RT and propagate that to RR2.
>>> >
>>> > RT-Constrain provides the ability to figure out what the interested
>>> > receivers are for a VPN defined by a route-target.  This provides a
>>> > restricted subset of the attached routers for propagation purposes.
>>> >
>>> > -- Jeff
>>> >
>>>
>>> _______________________________________________
>>> Idr mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/idr
>>>
>> --
>>
>> <http://www.verizon.com/>
>>
>> *Gyan Mishra*
>>
>> *Network Solutions A**rchitect *
>>
>>
>>
>> *M 301 502-134713101 Columbia Pike
>> <https://www.google.com/maps/search/13101+Columbia+Pike?entry=gmail&source=g> *Silver
>> Spring, MD
>>
>> _______________________________________________
>> Idr mailing list
>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/idr
>>
> --

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *



*M 301 502-134713101 Columbia Pike *Silver Spring, MD