Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inbound-02.txt
Robert Raszuk <robert@raszuk.net> Wed, 12 May 2021 21:50 UTC
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From: Robert Raszuk <robert@raszuk.net>
Date: Wed, 12 May 2021 23:33:30 +0200
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To: "Jakob Heitz (jheitz)" <jheitz@cisco.com>
Cc: Gyan Mishra <hayabusagsm@gmail.com>, Melchior Aelmans <melchior@aelmans.eu>, "idr@ietf. org" <idr@ietf.org>, Melchior Aelmans <maelmans@juniper.net>
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Subject: Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inbound-02.txt
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Jakob, Spot on. That is why I mentioned that the very same max-prefix when applied pre-policy vs post-policy can have a different value. But I guess this is implementation thing not so much an IETF draft one. Thx, R. On Wed, May 12, 2021 at 11:26 PM Jakob Heitz (jheitz) <jheitz@cisco.com> wrote: > The reason to terminate the session is illustrated in: > > > https://datatracker.ietf.org/meeting/104/materials/slides-104-grow-bgp-maximum-prefix-limits-00 > > > > Suppose you have a customer whose prefix advertisements vary somewhat, > > so you give him a decent margin. Suppose you set max-prefix to 1000 > > and on a fateful day he advertises 200 prefixes. > > You have some good inbound filters for him, but not perfect, again, > > because the prefixes he advertises vary somewhat. > > Now, on this day, he leaks the internet to you and you manage to filter > most of it out, > > but several routes sneak past your filter and leak. > > Those that sneak past your filter are not enough to trip your max-prefix > of 1000. > > If you have a pre-policy max-prefix of, say, 10000, that will easily catch > the leak > > and you could terminate the session to stop the leak. > > > > Regards, > > Jakob. > > > > *From:* Idr <idr-bounces@ietf.org> *On Behalf Of * Gyan Mishra > *Sent:* Wednesday, May 12, 2021 12:20 AM > *To:* Melchior Aelmans <melchior@aelmans.eu> > *Cc:* idr@ietf. org <idr@ietf.org>; Melchior Aelmans <maelmans@juniper.net>; > Robert Raszuk <robert@raszuk.net> > *Subject:* Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inbound-02.txt > > > > > > After thinking about it I agree that that the prefix pre and post can > definitely be different. The pre policy is a copy of the adj-rib-in stored > separately in memory so the limit values can definitely be different. In > such case as the pre policy is pre inbound filter so it can have a very > high water mark for maximum prefix, and the post policy would have the > maximum prefix exact value to trigger the neighbor being clamped down. In > general the trigger event peer being clamped down would happen on the post > policy adj-rib-in as that value would always be lower then the pre policy > adj-rib-in. In that respect thought I can’t see a scenario where the pre > policy maximum prefix would take down the peer over the post policy maximum > prefix. That being said I am not sure we really need a pre policy maximum > prefix. > > > > I understand the reason behind it to save on memory copy of tbt ash-rib-in > but I don’t think the action that the peer must be taken down if pre policy > maximum is exceeded if the post policy is not exceeded. The post policy > the control plane rib is programmed into hardware for forwarding so there > is more impact to resources both control and data plane for post policy as > opposed to pre policy is control plane copy and also is not advertised to > other peers as well as are pre policy prefixes. Much less impact if pre > policy is exceeded. > > > > I think the case where a peer advertisement went from 100k to 2M and the > pre policy was set to > > 1M and the post policy was set to 100k and 100k was received in this case > if it was a Must to clamp down the peer due to pre policy being exceeded > where post policy was not exceeded I don’t think that’s a good idea as is > impacting. I think for pre policy maybe only a warning should be allowed > but not clamping down the peer. > > > > Gyan > > > > > > On Tue, May 11, 2021 at 12:13 PM Melchior Aelmans <melchior@aelmans.eu> > wrote: > > Ack Robert, thanks for confirming. > > > > Cheers, > > Melchior > > > > On Tue, May 11, 2021 at 3:51 PM Robert Raszuk <robert@raszuk.net> wrote: > > Hi Melchior, > > > > After rethinking this I think the current text in the draft is ok. > > > > It is after all optional cfg and if vendor supports both pre and post > policy max-prefix limit inbound the configured numbers may not need to be > identical. > > > > Thx, > > R. > > > > > > On Tue, May 11, 2021 at 3:22 PM Melchior Aelmans <melchior@aelmans.eu> > wrote: > > Hi Robert, all, > > > > First of all thanks for your feedback! > > > > The part we are confused about is that soft-reconfiguration inbound is a > Cisco command to enable adj-RIB-In which then stores all the received > routes. On Juniper and OpenBGPd (and possibly other implementations as > well) adj-RIB-In is enabled by default and protected by a maximum-prefix > limit inbound. > > Could you please elaborate on what you are exactly trying to describe and > as Job suggested make suggestions for text adjustments? > > > > Thanks! > Melchior > > > > On Thu, Apr 15, 2021 at 4:36 PM Robert Raszuk <robert@raszuk.net> wrote: > > Hi Job, > > > > The distinction between Per and Post policy is clear. > > > > Inbound Prefix Limit may (depending on implementation) apply to either or > both of those processing stages. > > > > The observation I am trying to make is that IMHO soft in is not really a > Pre Policy in a sense that you must not apply Prefix Limit to it. Otherwise > the entire idea of soft-in becomes questionable. > > > > To me perhaps the proper way to visualize it is actually to divide Pre > Policy into two blocks - ALL Prefixes and Pre-Policy Prefix-Limited. All > Prefixes block would occur only when soft in is enabled. Otherwise some may > expect or request to apply Inbound Prefix Limit before routes are stored > when soft reconfiguration inbound is enabled. > > > > Or perhaps you actually want to do that sort of breaking that knob ? > > > > Many thx, > > R. > > > > > > > > > > > > > > On Thu, Apr 15, 2021 at 4:10 PM Job Snijders <job@fastly.com> wrote: > > Dear Robert, > > On Thu, Apr 15, 2021 at 02:16:12PM +0200, Robert Raszuk wrote: > > I think I have one question or suggestion. > > Your review is appreciated! > > > As you all know some implementations allow you to explicitly force BGP > > speaker to keep (pre-policy) all routes/paths received. > > > > Example: > > > > neighbor 192.168.1.1 soft-reconfiguration inbound > > > > The draft does not seem to comment on this case yet if implementation > > maintains the above behaviour at least some of the justifications for > > the document is gone. > > Interesting, the draft's objective is to clarify that inbound limits can > be applied at multiple stages of the pipeline (pre and post policy), not > all Network Operating Systems appear to offer this (operationally > speaking much needed) granularity, and through this draft we hope to > clarify to implementers that it is something worth considering to add. > > > I think that draft should at least mention such behaviour, not force to > > change it however put some light that if > > configured by the operator some of the benefits of inbound prefix limit > > will not be fully effective. > > What you call 'soft-reconfiguration inbound' ends up storing into what > the draft refers to as 'Pre Policy'. (At least... that is the intention, > it is possible the text is readable to us but not easy to understand for > others) > > Do you have specific text in mind to add to the draft to clarify this? > > Kind regards, > > Job > > _______________________________________________ > Idr mailing list > Idr@ietf.org > https://www.ietf.org/mailman/listinfo/idr > > _______________________________________________ > Idr mailing list > Idr@ietf.org > https://www.ietf.org/mailman/listinfo/idr > > -- > > <http://www.verizon.com/> > > *Gyan Mishra* > > *Network Solutions Architect * > > *Email gyan.s.mishra@verizon.com <gyan.s.mishra@verizon.com>* > > *M 301 502-1347* > > >
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Robert Raszuk
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Job Snijders
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Robert Raszuk
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Gyan Mishra
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… heasley
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Robert Raszuk
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Gyan Mishra
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… heasley
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Melchior Aelmans
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Robert Raszuk
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Melchior Aelmans
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Jakob Heitz (jheitz)
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Gyan Mishra
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Jakob Heitz (jheitz)
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Robert Raszuk
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Gyan Mishra
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… heasley
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Brian Dickson
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Gyan Mishra
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Melchior Aelmans
- Re: [Idr] I-D Action: draft-sas-idr-maxprefix-inb… Job Snijders