Re: [Idr] ttRE: FW: New Version Notification for draft-ietf-idr-bgp-open-policy-22.txt

[Susan Hares <[e-mail]>]

Bruno: 

 

The idr-chairs discussed your proposals.  Since Jeff kindly led the
discussion this week, Jeff is posting the IDR chairs response.   

As Jeff mentioned, we will be glad to sponsor a revision for RFC7606. 

 

Since you were kind enough to respond to me quickly, I have responded to
your questions from my view

As Jeff mentioned, we will be glad to sponsor a revision for RFC7606. 

 

Please let us know if this consensus call works for you. 

 

Again, Jeff, Keyur and I really appreciate you digging into the error cases.


We hope that other people will carefully read this discussion, and 

think about RFC7606.   If you wish to have a short presentation discussing
this topic 

at the next IETF, please let us know. 

 

Sue 

 

 

From: [e-mail] [mailto:[e-mail]] 
Sent: Friday, February 25, 2022 12:17 PM
To: Susan Hares
Cc: [e-mail]; [e-mail]; 'Alvaro Retana (aretana)'; 'Sriram,
Kotikalapudi (Fed)'
Subject: RE: [Idr] ttRE: FW: New Version Notification for
draft-ietf-idr-bgp-open-policy-22.txt

 

Hi Sue,

 

Thanks for your email.

Please see inline [Bruno3]

 

On a side note, I'm not even sure that the feature needs the attribute to
encode an AS number:

The AS number seems to be only checked in step "Ingress.2" when received
from a Peer.  However, there seem to be only 2 cases:

- if the EBGP neighbor supports OTC, it won't send the route if it's a leak
(OTC is present), so no need to double check on receipt as we won't receive
the route

- if the EBGP neighbor does not support OTC, it won't add the OTC with its
own AS number, so no need to check for this specific AS number an OTC would
not have this AS number.

 

Also, doesn't leaking the AS number in the OTC reveal some business
relationship that may be private? The security section does not seem to say
a word about this.

 

[Sue]:  [personal opinion]:  

Yes, it does reveal something.  The security section should mention it.  

Two caveats:  

1) Does it help operators to realize this point?  - If so, suggest some
wording that will be effective for the operators. 

2) Alvaro has reached an agreement on the text with the IESG.  We will need
Alvaro to approve any text changes as Ok with IESG's intent.  

 

From: Susan Hares <[e-mail]> 
Sent: Friday, February 25, 2022 3:25 PM



Bruno: 

 

One question which I am pulling to the front: 

 

1)      Why disable length checks? 

 

[Bruno3] Because on IBGP we don't even need to read this attribute and there
seem to be difficulties about defining how to react to error. So not
checking is possible and avoid the difficult discussion.

My preference would be to check and perform attribute discard on IBGP. But
some want to keep the OTC feature even though the attribute is bogus (while
the vast majority of routes are not leak so the probabilities would be that
the route is useful and should be kept, rather than treat-as-withdraw).

 

[Sue]: Jeff clearly states the chairs reasoning. 

 On IBGP, we need to check and  "treat-as-withdraw" behavior.  

I think this addresses your concern and the IDR chair's concern. 

 

Your comment : 

[Bruno2] First step that RFC7606 does is to define (i.e. choose) what
constitute an error. We could define that length is not checked for IBGP
because we don't care about the content (or even the attribute).
Alternatively, I'm also fine with attribute discard if we consider that the
attribute is in error and hence could not be trusted.

 

My point:  Length checks in RFC7606 seem basic sanity check for any message.


[Bruno3] Sure. That being said, for the CLUSTER_LIST attribute, there is a
different handling for EBGP and IBGP with IBGP checking for the length while
EBGP not checking the length
<https://datatracker.ietf.org/doc/html/rfc7606#section-7.10>
https://datatracker.ietf.org/doc/html/rfc7606#section-7.10

 

[sue]: I agree that the cluster list attribute has a different handling for
E-BGP and I-BGP. 

We discussed the pros/cons for OTC, but we think the "treat as withdraw' is
best. 

 

After that point, I am fine the remaining being specific to a draft.   For
example, OTC for IBGP can be tossed out after it is determined to have a
valid length. 

[Bruno3] I'm assuming that you meant "is determined to have an _invalid_
length".

 

[Sue]: First test for valid length.  If invalid, treat as withdraw.  

 

--Bruno

 

 

Did I miss some other reason.  

 

Thanks, Sue 

 

 

Orange Restricted

From: Idr [mailto:[e-mail]] On Behalf Of
[e-mail]
Sent: Wednesday, February 16, 2022 9:19 AM
To: Sriram, Kotikalapudi (Fed)
Cc: [e-mail]; [e-mail]; Alvaro Retana (aretana); Susan Hares
Subject: [Idr] ttRE: FW: New Version Notification for
draft-ietf-idr-bgp-open-policy-22.txt

 

Hi Sriram,

 

Please see inline [Bruno2]

 

 

Orange Restricted

From: Sriram, Kotikalapudi (Fed) <[e-mail]> 
Sent: Tuesday, February 15, 2022 11:52 PM
To: DECRAENE Bruno INNOV/NET <[e-mail]>; Alexander Azimov
<[e-mail]>; Jeffrey Haas <[e-mail]>
Cc: [e-mail]; Alvaro Retana (aretana) <[e-mail]>;
[e-mail]; Susan Hares <[e-mail]>
Subject: RE: [Idr] FW: New Version Notification for
draft-ietf-idr-bgp-open-policy-22.txt

 

Hi Bruno,

 

Comments inline marked with [Sriram].

 

>[Bruno] - RFC7606 provides a guidance
https://datatracker.ietf.org/doc/html/rfc7606#section-8
<https://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatrack
er.ietf.org%2Fdoc%2Fhtml%2Frfc7606%23section-8&data=04%7C01%7Ckotikalapudi.s
riram%40nist.gov%7Cb7a059d3cee145ca531c08d9f0a3c35f%7C2ab5d82fd8fa4797a93e05
4655c61dec%7C1%7C0%7C637805408436586543%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4w
LjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Fsbz%2B8
gTR8c0r94m4SoaamR4O%2BmHiMYH5tY9uRCXTHk%3D&reserved=0>  . It's only half a
page so anyone interested could read. I don't think it can be summarized as
per you above sentence. 

 

[Sriram] Section 8 of RFC 7606 that you cite, says:

 

   A document that specifies a new BGP attribute MUST provide specifics

   regarding what constitutes an error for that attribute and how that

   error is to be handled.  Allowable error-handling approaches are

   detailed in Section 2.

 

[Sriram] From the list of error-handling approaches detailed in Section 2,
only treat-as-withdraw and attribute discard are relevant for us. Since the
RFC says, "Allowable error-handling approaches are detailed in Section 2",
it does not allow for applying none of the approaches as an option.

 

[Bruno2] First step that RFC7606 does is to define (i.e. choose) what
constitute an error. We could define that length is not checked for IBGP
because we don't care about the content (or even the attribute).
Alternatively, I'm also fine with attribute discard if we consider that the
attribute is in error and hence could not be trusted.

 

>[Bruno] In particular there is not such "SHALL be handled using the
approach of "treat-as-withdraw". 

 

[Sriram] Regarding attribute discard, RFC 7606 says: "This approach MUST NOT
be used except in the case of an attribute that has no effect on route
selection or installation." This implies: This approach MUST NOT be used in
the case of an attribute that has an effect on route selection or
installation. Do you agree? The route does propagate from iBGP (ingress) to
eBGP (in the ASBR), where the attribute plays a role in route selection for
propagation. 

 

[Bruno2] 1) For IBGP, OTC attribute has no effect on route selection and
installation. 2) Since you seem to be calling for "treat-as-withdraw", I
would argue that "treat-as-withdraw" has also an effect on route selection
or installation, and a bigger one. So it's not really safer in term of side
effect.

 

>[Bruno] It also specifically calls for attention to optional transitive
attributes (such as OTC) for which "the damage inflicted may be multiplied
manyfold >

 

[Sriram] The "damage inflicted may be multiplied manyfold" is about session
reset. That is why the RFC urges the use of treas-as-withdraw or attribute
discard instead.

[Bruno2] It's discussed in the context as session reset, but the cause is
the optional transitive attribute. Cf following text which only refers to
the type of attribute and not the action taken

   although the problematic attributes may have

   originated with a single update transmitted by a single BGP speaker,

   by the time they encounter a router that checks them they may have

   been replicated many times and thus may cause the reset of many

   peering sessions.  Thus, the damage inflicted may be multiplied

   manyfold.

 

 

 

>[Bruno] Without double checking, I don't recall that OTC is acted upon
within IBGP. So in this case it does not affect routing selection. Let's
just specify to not even look at it (it's optional) and problem is solved.

 

[Sriram] iBGP and eBGP within an ASBR are not isolated operations. Please
see my comment above.

Not to look at OTC is not an option.

[Bruno2] If this were true, we could not define the OTC as an optional
transitive attribute, because essentially some routers will not look at OTC.
Pick your option.

 

 

A compliant router checks syntax errors in iBGP (just as in eBGP) based on
its expectations of the OTC Attribute. If the length value does not match,
the Attribute is malformed. 

 

[Sriram] If the OTC attribute is malformed for any reason, we cannot be sure
that even the Attribute type value is correct (or as intended). 

[Bruno2] 1) That's not the path chosen by RFC 7606 in case of a length
error. 2) I would find debatable to assume an error on a field (type) when
you don't see an error on this field. TLV construct provides hierarchy: I
agree that what is inside the TLV (i.e. after/below the error) can't be
trusted; but for what is before the error, there is little to no reason to
assume an error (and if we do, we could imagine anything and in particular
an attribute for which the error handling is "session reset".)

 

[Sriram] Then must it be propagated from iBGP to eBGP (in the ASBR) and then
to eBGP neighbors? 

[Bruno2] Current text proposes to _not_ propagate to eBGP neighbors except
for Customer. If length is wrong, I would be fine to also not propagate to
Customerif you find this better.

 

Thanks for the discussion

--Bruno

 

Thanks.

 

Sriram

 

 

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