Re: [Idr] IETF LC for IDR-ish document <draft-ietf-grow-bgp-reject-05.txt> (Default EBGP Route Propagation Behavior Without Policies) to Proposed Standard

Enke Chen <enkechen@cisco.com> Sun, 23 April 2017 20:01 UTC

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To: Mikael Abrahamsson <swmike@swm.pp.se>
References: <68B29403-9AD9-4F06-9FE4-3F077E793D9F@puck.nether.net> <275cf744-1f64-bcbc-dabe-a47479921230@cisco.com> <20170420154142.lacvtplusepy3qcf@hanna.meerval.net> <b57162ec-f806-6e86-7713-58608f72c468@cisco.com> <32C0B4EE-6241-49F9-97F2-7107AC68678D@juniper.net> <e513849d-f895-0499-7bf4-5ecb24cadab7@cisco.com> <4CE4AF1E-0C80-423E-B19D-5750FCAFAD89@juniper.net> <23283_1492759950_58F9B58E_23283_375_1_53C29892C857584299CBF5D05346208A31CC352B@OPEXCLILM21.corporate.adroot.infra.ftgroup> <20170421084638.l6pbvtznfsxnq2wy@Vurt.local> <23291_1492766305_58F9CE61_23291_9725_1_53C29892C857584299CBF5D05346208A31CC399E@OPEXCLILM21.corporate.adroot.infra.ftgroup> <20170421095839.sralcy7aos5mzzic@Vurt.local> <d57ed214-945a-54b8-e04f-cb8610f789e4@cisco.com> <alpine.DEB.2.02.1704231447550.5591@uplift.swm.pp.se>
Cc: "idr@ietf.org" <idr@ietf.org>, Enke Chen <enkechen@cisco.com>
From: Enke Chen <enkechen@cisco.com>
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Date: Sun, 23 Apr 2017 13:01:21 -0700
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Subject: Re: [Idr] IETF LC for IDR-ish document <draft-ietf-grow-bgp-reject-05.txt> (Default EBGP Route Propagation Behavior Without Policies) to Proposed Standard
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Hi, Mikael:

On 4/23/17 5:56 AM, Mikael Abrahamsson wrote:
> On Fri, 21 Apr 2017, Enke Chen wrote:
> 
>> Job,
>>
>> IMO the most important point from the discussion is that any BGP extension
>> or behavior change must be backward compatible, which this document is lacking
>> or even missing.  After more than 20 years of BGP deployment, the world is no
>> longer "green field" any more.
> 
> I have been involved in running core networks since late 90ties. I've deployed
> several vendors gear. Yes, going from IOS to IOS XR with the change to XR having
> default deny if there is no policy, that was a single occasion "oh", and then I
> knew that. The good part here is that it's failsafe "close", so that you don't announce
> anything by accident. In IOS you have to basically paste two lines at once, with
> the first line being the creation of the neighbor, the second line being shutdown. 
> Then you can configure the rest. Otherwise there is a race condition in the immediacy
> of a per-line, immediate committing operating system such as IOS.

I think the premature session bring up is fixable. Your email has been forwarded to
the IOS development team.

> 
> This is just bad design. It's "fail open" default. If you somehow fail to paste that
> second shutdown line, you're now fully-open, announcing and accepting all routes.
> 
> If IOS would be changing its defaults, the CLI line migration code could by default
> insert a PERMIT-ALL policy statement, or some other means where an upgrade would keep 
the behaviour of the box intact across operating system versions.
> 
> So I fully support draft-ietf-grow-bgp-reject-05 because it just makes more operational
> sense than the old default that for instance IOS implements. We need default fail-close,
> because it just creates less problems than default fail-open.
> 

> If this doesn't make sense, why was it chosen for IOS XR back in the early 00ds?

I don't think that folks are saying this "deny all" doe not make sense.  When you
start a *new* software, certainly you are free to choose a default based on the most
up-to-date knowledge.

As I understand, that was the case for IOS XR as a new and separate software release.
 
Regards,  -- Enke