Subject: Re: [GROW] I-D Action: draft-ymbk-grow-wkc-behavior-00.txt

From: Gert Doering <[email-masked]>
Date: Thu, 1 Mar 2018 09:15:09 +0100

Hi,

On Thu, Mar 01, 2018 at 09:52:37AM +0900, Randy Bush wrote:
> question for ops:
> 
>   did you even know this was happening, that "set community" might not
>   replace ALL well known communities?"

No, as in, "I assumed that 'set community' would stamp the communities
listed onto the prefix, and replace everything already there".  

For "not replace things", there is "set community .. additive".

(I'd need to go and check our platforms, and from this mail thread I assume
I will find surprises)

Gert Doering
        -- NetMaster
-- 
have you enabled IPv6 on something today...?

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---

From: Randy Bush <[email-masked]>
Date: Thu, 01 Mar 2018 17:37:19 +0900

>> did you even know this was happening, that "set community" might
>> not replace ALL well known communities?"
> 

jay was shocked when he discovered it, and i was shocked when he told
me.

but we worry that calling it a bug and asking it be fixed might break
someone's network.  waiting for folk to speak up.  hence the nanog
posting.

randy

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From: Job Snijders <[email-masked]>
Date: Thu, 1 Mar 2018 12:50:27 +0000

On Wed, Feb 28, 2018 at 09:52:50PM -0500, Jay Borkenhagen wrote:
> For what it's worth, I first noticed the special treatment of some
> well-known communities after Job announced his GRACEFUL_SHUTDOWN
> beacon prefix.  I expected that it would not have passed intact
> through a "set community foo" policy, but it did.
> 
> Clearly "set community foo" is not appropriate for use on many classes
> of connections -- e.g. on connections to one's customers -- but where
> it is used it should not cause surprises.

I agree that surprises are bad. What I struggle with is defining what
the sensible non-surprising behaviour is.

IOS XR:   "set community X" removes _all_ except WKC, and sets X
Junos:    "set community X" removes _all_, and sets X
OpenBGPD: "set community X" is the equivalent of "set community X additive"
BIRD:     "set community X" doesn't exist
ExaBGP:   "set community X" doesn't exist
etc...

Kind regards,

Job

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From: "i3D.net - Martijn Schmidt" <[email-masked]>
Date: Thu, 1 Mar 2018 13:56:34 +0100

> ExaBGP:   "set community X" doesn't exist
Brocade NetIron also behaves like: "set community X" removes _all_, and
sets X

To be honest, I am also surprised there is so much variance. Perhaps
this explains why real-world incidents such as last November's
Level3<>Comcast leak happen. That seemed to be the result of a stripped
no-export community..

Link:
https://dyn.com/blog/widespread-impact-caused-by-level-3-bgp-route-leak/

---

From: Randy Bush <[email-masked]>
Date: Fri, 02 Mar 2018 07:26:21 +0900

> IOS XR:   "set community X" removes _all_ except WKC, and sets X
                                                  ^ some
randy