Subject: [Idr] optional transitive - recognised but out of context

From: "iLya" <[email-masked]>
Date: Tue, 20 Sep 2011 09:10:41 +0200

Hi,

yesterday and few days earlier several people have observed their BGP 
sessions being reset after seeing certain prefix. After some evaluation I've 
found that offending prefix (in global internet table) had optional 
transitive ATTR_SET (code 128) attached. Not having first hand access to 
platforms that exhibited session reset I'm speculating that they've 
recognised attribute as such but found it to be inappropriate for given 
context and so treated update as malformed with all consequences.

BGP specs seem to have only one place that could (with some stretching) 
justify such behaviour - from rfc4271#section-6.3 "...If an optional 
attribute is recognized, then the value of this attribute MUST be 
checked...". Wouldn't it be appropriate to add extra text that would clarify 
that optional transitive attributes out of context should not result in 
session reset?

P.S.: as far as I understood problematic BGP implementation is fixed in 
later software releases, but lack of clarity in BGP specs leaves room for 
similar problems in the future

Cheers,
iLya

---

From: Robert Raszuk <[email-masked]>
Date: Tue, 20 Sep 2011 09:35:25 +0200

Hi Ilya,

Do you think that the below draft still does not formally address the 
problem you are describing ?

http://tools.ietf.org/html/draft-ietf-idr-optional-transitive-03

Cheers,
R.

> sessions being reset after seeing certain prefix. After some evaluation
> I've found that offending prefix (in global internet table) had optional
> checked...". Wouldn't it be appropriate to add extra text that would
> clarify that optional transitive attributes out of context should not
> result in session reset?
>
> later software releases, but lack of clarity in BGP specs leaves room
> for similar problems in the future
>
> Cheers,
> iLya
>
>
> _______________________________________________
> Idr mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/idr
>
>

---

From: "iLya" <[email-masked]>
Date: Tue, 20 Sep 2011 10:39:19 +0200

Hi Robert,

--------------------------------------------------
> http://tools.ietf.org/html/draft-ietf-idr-optional-transitive-03

it goes in the right direction but stops short of saying whether recognised 
optional transitive attribute (partial or not) properly formed but out of 
context (e.g. L3VPN-specific attribute in global table) is an error or not. 
If authors of draft-ietf-idr-optional-transitive-03 consider the problem 
I've described to be within scope of the draft and could address it more 
explicitly, that would do.

Cheers,
iLya

---

From: Juan Alcaide <[email-masked]>
Date: Tue, 20 Sep 2011 07:49:27 -0400 (EDT)

iLya,

As I read it:

The draft only deals with malformed attributes. So it doesn't apply

To deal with optional attributes that are recognized, you have to refer to 
specific RFC/describing the specific attribute. For some attributes, it 
may be ok to reset, for others not. RFC4271:6.3 won't tell you what to do 
about an attribute that it's not defined there.

Unfortunately, this part is often missed.

2c,

-Juan

On Tue, 20 Sep 2011, iLya wrote:

> If authors of draft-ietf-idr-optional-transitive-03 consider the problem I've 
> described to be within scope of the draft and could address it more

---

From: Paul Jakma <[email-masked]>
Date: Tue, 20 Sep 2011 13:44:32 +0100 (BST)

On Tue, 20 Sep 2011, Robert Raszuk wrote:

> Hi Ilya,
>
> Do you think that the below draft still does not formally address the problem 
> you are describing ?
>

Hmm, is it just me or does that not appear in the IDR docs page?

regards,
-- 
Paul Jakma  [email-masked]  twitter: @pjakma  PGP: 64A2FF6A
Fortune:
NEWS FLASH!!
Today the East German pole-vault champion became the West German pole-vault
champion.

---

From: "t.petch" <[email-masked]>
Date: Tue, 27 Sep 2011 11:57:46 +0200

Paul

I can get it but it does say
"Expires: April 1, 2011  "
so perhaps I shouldn't:-(

Tom Petch

----- Original Message -----
From: "Paul Jakma" <[email-masked]>
To: "Robert Raszuk" <[email-masked]>
Cc: <[email-masked]>
Sent: Tuesday, September 20, 2011 2:44 PM
Subject: Re: [Idr] optional transitive - recognised but out of context

> > Do you think that the below draft still does not formally address the
problem