Hi Rudy,
please see inline:
On 17/06/2021 15:38, Selderslaghs, Rudy (Nokia - BE/Antwerp) wrote:
Hi Les,
The question remains whether an ISIS Appl-Spec-SRLG TLV with SABML 0 and
UDABML 0 means that it is valid for all applications or not.
This is currently not specified in RFC8919.
Secondly the approach to handle ISIS Appl-Spec-SRLG TLVs independently
from ASLA sub-TLVs in the context of overruling “All-Appl” attributes,
creates confusion in BGP-LS in my opinion.
Take the following example with TLV’s belonging to the same link:
IS-Neighbors TLV
ASLA TLV
SABML 0, UDABML 0 (= All Appl)
TE-Metric 20
Appl-Spec-SRLG TLV
SABML 1, UDABML 0, Bitmap SR-Policy
SRLG 1
Following your answer, SR-Policy has to use TE-Metric 20 and SRLG 1.
Now suppose that the node that receives this ISIS advertisement has to
pass this on to a server via BGP-LS, this will be the result:
Link Attributes:
ASLA TLV
SABML 0, UDABML 0 (= All Appl)
TE-Metric 20
ASLA TLV
SABML 1, UDABML 0, Bitmap SR-Policy
SRLG 1
The server that receives this BGP-LS advertisement, has to take into
account that it comes from the ISIS protocol in order to treat the ASLA
TLV with SRLG info independently (as ISIS is supposed to do). I.e. the
ASLA TLV with SRLG info does not overrule the first ASLA TLV and the
server has to use TE-Metric 20 and SRLG 1 for SR-Policy.
If the server would receive the same BGP-LS advertisement for the OSPF
protocol, it can only use SRLG 1 for SR-Policy, because the second ASLA
TLV overrules the first one in line with the OSPF rules.
I think this is confusing and that it is more consistent to treat an
ISIS Appl-Spec-SRLG TLV as an ASLA TLV in the context of overruling of
“All-Appl” attributes.
The fact that ISIS transports SRLG info via a separate TLV seems no
reason to me to treat it independent of ASLA TLV’s.
the above problem is the result of the different encoding of the same
data in ISIS and BGP-LS.
From the ISIS perspective, there are two independent TLVs:
a) Application-Specific Link Attributes TLV
b) Application-Specific SRLG TLV
Each of these carry it's own Application Identifier Bit Mask and carry
disjoint set of attributes. We clearly can not mix these TLVs together.
BGP-LS only has the single Application Specific Link Attributes TLV,
that is mixing SRLGs with other link attributes.
To be able to interpret the BGP-LS data on the receiver in a protocol
independent way, the BGP-LS originator would have to 'translate' the
ISIS AS SRLGs consistently with the BGP-LS encoding - that would have to
be done in draft-ietf-idr-bgp-ls-app-specific-attr. We will work on that
and update that draft.
From the ISIS perspective the behavior is unchanged - the
Application-Specific SRLG TLVs have to be treated independently of the
Application-Specific Link Attributes TLVs.
thanks,
Peter
Thanks,
Rudy
*From:*Lsr <lsr-boun...@ietf.org> *On Behalf Of *Shraddha Hegde
*Sent:* Thursday, June 17, 2021 7:14 AM
*To:* Les Ginsberg (ginsberg) <ginsb...@cisco.com>; Van De Velde, Gunter
(Nokia - BE/Antwerp) <gunter.van_de_ve...@nokia.com>; lsr@ietf.org
*Cc:* DECRAENE Bruno IMT/OLN <bruno.decra...@orange.com>
*Subject:* Re: [Lsr] Proposed Errata for RFCs 8919/8920
Les,
Whether ASLA sub-TLV is present in IS-Neighbor TLV and whether it has
zero-length ABM on non-zero-length ABM is irrelevant to the use of ASLA SRLG
TLV – and vice versa.
Can you state this explicitly in the document?
Rgds
Shraddha
Juniper Business Use Only
*From:*Les Ginsberg (ginsberg) <ginsb...@cisco.com
<mailto:ginsb...@cisco.com>>
*Sent:* Wednesday, June 16, 2021 10:31 PM
*To:* Van De Velde, Gunter (Nokia - BE/Antwerp)
<gunter.van_de_ve...@nokia.com <mailto:gunter.van_de_ve...@nokia.com>>;
Shraddha Hegde <shrad...@juniper.net <mailto:shrad...@juniper.net>>;
lsr@ietf.org <mailto:lsr@ietf.org>
*Cc:* DECRAENE Bruno IMT/OLN <bruno.decra...@orange.com
<mailto:bruno.decra...@orange.com>>
*Subject:* RE: Proposed Errata for RFCs 8919/8920
*[External Email. Be cautious of content]*
Gunter –
There is no relationship between the ASLA SRLG TLV and IS-Neighbor TLV.
I do not understand why you would think that there is.
Whether ASLA sub-TLV is present in IS-Neighbor TLV and whether it has
zero-length ABM on non-zero-length ABM is irrelevant to the use of ASLA
SRLG TLV – and vice versa.
Les
*From:*Van De Velde, Gunter (Nokia - BE/Antwerp)
<gunter.van_de_ve...@nokia.com <mailto:gunter.van_de_ve...@nokia.com>>
*Sent:* Wednesday, June 16, 2021 9:07 AM
*To:* Shraddha Hegde <shrad...@juniper.net
<mailto:shrad...@juniper.net>>; Les Ginsberg (ginsberg)
<ginsb...@cisco.com <mailto:ginsb...@cisco.com>>; lsr@ietf.org
<mailto:lsr@ietf.org>
*Cc:* DECRAENE Bruno IMT/OLN <bruno.decra...@orange.com
<mailto:bruno.decra...@orange.com>>
*Subject:* RE: Proposed Errata for RFCs 8919/8920
Another item of ambiguity is whether “wildcarding” applies also to the
ISIS TE-Appl-Spec-SRLG TLV.
It seems that the RFC8919 does not specify it.
Note: for OSPF the wildcarding also applies to SRLG info because it is
transported via the same container TLV as the other TE attributes.
_Example 1_
TE-IS-NBRs TLV
Link x
ASLA TLV
SABML 0, UDABML 0 (= All Appl)
TE-Metric 20
TE-Appl-Spec-SRLG TLV
Link x
SABML 1, UDABML 0, Bitmap Flex-Algo
SRLG 1 2 3
Should TE-Metric 20 be used for Flex-Algo or not ?
In other words, is the wildcard ASLA TLV overruled by the specific
TE-Appl-Spec_SRLG TLV or not ?
_Example 2_
Maybe this is an invalid example if wildcarding does not apply for the
TE-Appl-SRLG TLV.
TE-IS-NBRs
Link x
ASLA TLV
SABML 1, UDABML 0, Bitmap Flex-Algo
TE-Metric 20
TE-Appl-Spec-SRLG
Link x
SABML 0, UDABML 0 (= All Appl)
SRLG 1 2 3
Should SRLG 1 2 3 be used for Flex-Algo or not ?
What is your opinion ?
G/
*From:*Shraddha Hegde <shrad...@juniper.net <mailto:shrad...@juniper.net>>
*Sent:* Wednesday, June 16, 2021 4:46 PM
*To:* Les Ginsberg (ginsberg) <ginsberg=40cisco....@dmarc.ietf.org
<mailto:ginsberg=40cisco....@dmarc.ietf.org>>; lsr@ietf.org
<mailto:lsr@ietf.org>
*Cc:* DECRAENE Bruno IMT/OLN <bruno.decra...@orange.com
<mailto:bruno.decra...@orange.com>>; Van De Velde, Gunter (Nokia -
BE/Antwerp) <gunter.van_de_ve...@nokia.com
<mailto:gunter.van_de_ve...@nokia.com>>
*Subject:* RE: Proposed Errata for RFCs 8919/8920
Hi,
I think that there may still be some ambiguity arising from the text
below due to the fact that
There are attributes such as maximum-link-bandwidth which have special
behaviour mentioned in later sections.
"Link attributes MAY be advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and
user-defined applications.
Such advertisements MUST be used by standard applications and/or user
defined applications when no link attribute advertisements with a
non-zero-length
Application Identifier Bit Mask and a matching Application Identifier
Bit set are present for a given link. Otherwise, such advertisements
MUST NOT be used."
For example, If max link bandwidth attribute comes in a
Zero length SABM & UDABM and we have a Flex-algo specific ASLA
that does not have the max-link-bandwidth advertised, can
Flex-algo use max-link-bandwidth attribute?
My interpretation from modified text for ISIS is that, it cannot use it.
I think there is no harm in re-iterating in order to avoid people
reading is differently.
Link attributes MAY be advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and
user-defined applications.
Such advertisements MUST be used by standard applications and/or user
defined applications when no link attribute advertisements with a
non-zero-length
Application Identifier Bit Mask and a matching Application Identifier
Bit set are present for a given link. Otherwise, such advertisements
MUST NOT be used.
*In other words,
When an application specific link Attribute sub-TLV is advertised with
one or more specific
standard application or user defined application bits set, all link
attributes that are allowed in ASLA MUST
be used from the ASLA sub-TLVs having that specific application bit set.
For the purposes of such applications, link attributes MUST NOT be used from
ASLA sub-TLV with zero SABM & UDABM length*.
Rgds
Shraddha
Juniper Business Use Only
*From:*Lsr <lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org>> *On
Behalf Of *Les Ginsberg (ginsberg)
*Sent:* Tuesday, June 15, 2021 8:55 PM
*To:* lsr@ietf.org <mailto:lsr@ietf.org>
*Cc:* DECRAENE Bruno IMT/OLN <bruno.decra...@orange.com
<mailto:bruno.decra...@orange.com>>; Van De Velde, Gunter (Nokia -
BE/Antwerp) <gunter.van_de_ve...@nokia.com
<mailto:gunter.van_de_ve...@nokia.com>>
*Subject:* [Lsr] Proposed Errata for RFCs 8919/8920
*[External Email. Be cautious of content]*
Folks -
Recent discussions on the list have highlighted some unintentional
ambiguity in how ASLA advertisements are to be used. Please see
https://mailarchive.ietf.org/arch/msg/lsr/prSLJDkMUnHm6h7VuCdn_Q7-1vg/
<https://urldefense.com/v3/__https:/mailarchive.ietf.org/arch/msg/lsr/prSLJDkMUnHm6h7VuCdn_Q7-1vg/__;!!NEt6yMaO-gk!RK_eZNNu1y0aJvAqIaNwHTIFAjHWFJwW1UqyOO8ACxB0kof3jmD_dRkiPkbVLJyA$>
The following proposed Errata address this ambiguity and aligns language
in the two RFCs.
We welcome comments on the proposed Errata before officially filing them.
Les and Peter
/Errata Explanation/
//
/Both RFC 8919 and RFC 8920 define advertising link attributes with zero
length Standard Application Bit Mask (SABM) and zero length User Defined
Application Bit Mask (UDABM) /
/as a means of advertising link attributes that can be used by any
application. However, the text uses the word "permitted", suggesting
that the use of such advertisements is "optional". /
/Such an interpretation could lead to interoperability issues and is not
what was intended./
//
/The replacement text below makes explicit the specific conditions when
such advertisements MUST be used and the specific conditions under which
they MUST NOT be used./
//
*/RFC 8919 Section 4.2:/*
//
/OLD/
//
*/"If link attributes are advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and
user-defined applications, /*
*/then any standard application and/or any user-defined application is
permitted to use that set of link attributes so long as there is not
another set of attributes/*
*/advertised on that same link that is associated with a non-zero-length
Application Identifier Bit Mask with a matching Application Identifier
Bit set."/*
//
/NEW/
//
*/"Link attributes MAY be advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and
user-defined applications. /*
*/Such advertisements MUST be used by standard applications and/or user
defined applications when no link attribute advertisements with a
non-zero-length /*
*/Application Identifier Bit Mask and a matching Application Identifier
Bit set are present for a given link. Otherwise, such advertisements
MUST NOT be used."/*
//
*/RFC 8919 Section 6.2/*
//
/OLD/
//
*/"Link attribute advertisements associated with zero-length Application
Identifier Bit Masks for both standard applications and user-defined
applications are usable/*
*/by any application, subject to the restrictions specified in Section
4.2. If support for a new application is introduced on any node in a
network in the presence of such/*
*/advertisements, these advertisements are permitted to be used by the
new application. If this is not what is intended, then existing
advertisements MUST be readvertised/*
*/with an explicit set of applications specified before a new
application is introduced."/*
//
//
/NEW/
//
*/"Link attribute advertisements associated with zero-length Application
Identifier Bit Masks for both standard applications and user-defined
applications are usable /*
*/by any application, subject to the restrictions specified in Section
4.2. If support for a new application is introduced on any node in a
network in the presence of such /*
*/advertisements, the new application will use these advertisements,
when the aforementioned restrictions are met. If this is not what is
intended, then existing /*
*/advertisements MUST be readvertised with an explicit set of
applications specified before a new application is introduced."/*
*//*
*//*
//
*/RFC 8920 Section 5/*
*//*
/OLD/
//
*/"If link attributes are advertised with zero-length Application
Identifier Bit Masks for both standard applications and user-defined
applications, /*
*/then any standard application and/or any user-defined application is
permitted to use that set of link attributes. If support for a new
application /*
*/is introduced on any node in a network in the presence of such
advertisements, these advertisements are permitted to be used by the new /*
*/application. If this is not what is intended, then existing
advertisements MUST be readvertised with an explicit set of applications
specified /*
*/before a new application is introduced./*
*//*
*/An application-specific advertisement (Application Identifier Bit Mask
with a matching Application Identifier Bit set) for an attribute MUST /*
*/always be preferred over the advertisement of the same attribute with
the zero-length Application Identifier Bit Masks for both standard /*
*/applications and user-defined applications on the same link."/*
*//*
/NEW/
//
*/"Link attributes MAY be advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and
user-defined applications. /*
*/Such advertisements MUST be used by standard applications and/or user
defined applications when no link attribute advertisements with a
non-zero-length /*
*/Application Identifier Bit Mask and a matching Application Identifier
Bit set are present for a given link. Otherwise, such advertisements
MUST NOT be used."/*
//
//
//
*/RFC 8920 New Section between 12.1 and 12.2. Current sections following
this new section will need to be renumbered./*
//
//
*/12.2 Use of Zero-Length Application Identifier Bit Masks/*
*//*
*/"Link attribute advertisements associated with zero-length Application
Identifier Bit Masks for both standard applications and user-defined
applications are usable /*
*/by any application, subject to the restrictions specified in Section
5. If support for a new application is introduced on any node in a
network in the presence of such /*
*/advertisements, the new application will use these advertisements,
when the aforementioned restrictions are met. If this is not what is
intended, then existing /*
*/advertisements MUST be readvertised with an explicit set of
applications specified before a new application is introduced."/*
//
//
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