Subject: Re: [Lsr] AD Review of draft-ietf-ospf-ospfv2-hbit-06

From: Alvaro Retana <[email-masked]>
Date: Tue, 12 Feb 2019 13:26:41 -0800

Ping!

Any progress on this document?

Thanks!

Alvaro.

On December 17, 2018 at 8:22:25 AM, Acee Lindem (acee) ([email-masked])
wrote:

Hi Padma,
Is the updated draft coming soon?
Thanks,
Acee

On 11/28/18, 2:31 PM, "Padmadevi Pillay Esnault" <[email-masked]> wrote:

Dear Alvaro

Thank you for your review.

We will go through the comments and work on them.

Thanks
Padma on behalf of my co-authors

On 11/28/18, 7:53 AM, "Alvaro Retana" <[email-masked]> wrote:

Dear authors:

I just finished reading this document. Even though it is relatively short,
I have significant concerns and I think it needs more work. Please take a
look at the detailed comments in-line below -- I'm highlighting some of the
issues here.

(1) What is the Update to rfc2328? Please be specific in both the Abstract
and the Introduction to indicate how rfc2328 is Updated. Also, see my
question about rfc6987 in §6.

(2) Operational/Deployment Considerations. There are several places
(specially in §3) where the specification offers a choice (e.g. by using
MAY). Some of those choices would be better informed if there was a
discussion of the considerations behind them. Please take a look at
rfc5706 (specially §2). Either a discussion close to where the behavior is
specified or a separate section is ok. Please also keep migration in mind
(see comments in §5).

(3) Both the IANA and Security Considerations sections need more details.

I will wait for them to be addressed before starting the IETF Last Call.

Thanks!

Alvaro.

[The line numbers come from idnits.]

...
11 H-bit Support for OSPFv2
12 draft-ietf-ospf-ospfv2-hbit-06

[nit] Please make the title more descriptive. "non-transit router", "host
mode", etc. come to mind.

14 Abstract

16 OSPFv3 defines an option bit for router-LSAs known as the R-bit in
17 RFC5340. If the R-bit is clear, an OSPFv3 router can participate in
18 OSPF topology flooding, however it will not be used as a transit
19 router. In such cases, other routers in the OSPFv3 routing domain
20 only install routes to allow local traffic delivery. This document
21 defines the H-bit functionality to prevent other OSPFv2 routers from
22 using the router for transit traffic in OSPFv2 routing domains as
23 described in RFC 2328. This document updates RFC 2328.

[minor] Describing the functionality in terms of OSPFv2 would have been
nice. IOW, there's no need (in the Abstract) to force the reader to go
figure out what OSPFv3 already did to decide if it's worth reading this
document or not.

[major] What is the Update to rfc2328? Please be specific, both here and
in the Introduction: don't just mention the section updated, but (more
important) what is the update about. "This document updates rfc2328 by
assigning a bit...changing the SPF process...creating a registry..."
All/none/something else?

Note that the answer to "what is the update?" doesn't have to be all. I
think that the registry creation is a must. But Updating because of the
SPF changes means that you expect an rfc2328 implementation to consider the
H-bit when running SPF. I think you really mean that implementations of
this document (i.e. not all rfc2328 implementations) have to use the
modified SPF. That is my guess...please consider the answer carefully.

...
42 Copyright Notice

44 Copyright (c) 2018 IETF Trust and the persons identified as the
45 document authors. All rights reserved.

47 This document is subject to BCP 78 and the IETF Trust's Legal
48 Provisions Relating to IETF Documents
49 (https://trustee.ietf.org/license-info) in effect on the date of
50 publication of this document. Please review these documents
51 carefully, as they describe your rights and restrictions with respect
52 to this document. Code Components extracted from this document must
53 include Simplified BSD License text as described in Section 4.e of
54 the Trust Legal Provisions and are provided without warranty as
55 described in the Simplified BSD License.

57 This document may contain material from IETF Documents or IETF
58 Contributions published or made publicly available before November
59 10, 2008. The person(s) controlling the copyright in some of this
60 material may not have granted the IETF Trust the right to allow
61 modifications of such material outside the IETF Standards Process.
62 Without obtaining an adequate license from the person(s) controlling
63 the copyright in such materials, this document may not be modified
64 outside the IETF Standards Process, and derivative works of it may
65 not be created outside the IETF Standards Process, except to format
66 it for publication as an RFC or to translate it into languages other
67 than English.

[major] As far as I can tell, the first version of
draft-keyupate-ospf-ospfv2-hbit (the predecessor of this document) was
published in 2015. So the copyright text above doesn't apply. Are we
missing other predecessors?

If not, then this issue should be easy to fix. In at least the XML editor
that I use, there's an option to indicate pre-RFC5378 work, or not. In
this case it seems like it should be No.

...
85 1. Introduction

[minor] Same comment as for the Abstract: describing the functionality in
terms of OSPFv2 would have been nicer. You can still make the reference to
the R-bit at the end, if you really want to.

87 OSPFv3 [RFC5340] defines an option bit for router-LSAs known as the
88 R-bit. If the R-bit is clear, an OSPFv3 router can participate in
89 OSPFv3 topology flooding without acting as a transit router. In such
90 cases, other routers in the OSPFv3 routing domain only install routes
91 used for local traffic.

93 This functionality is particularly useful for BGP Route Reflectors,
94 known as virtual Route Reflectors (vRRs), that are not in the
95 forwarding path but are in central locations such as data centers.
96 Such Route Reflectors typically are used for route distribution and
97 are not capable of forwarding transit traffic. However, they need to
98 learn the OSPF topology for:

100 1. SPF computation for Optimal Route Reflection functionality as
101 defined in [I-D.ietf-idr-bgp-optimal-route-reflection]

103 2. Reachability resolution for its Route Reflector Clients.

[nit] Clearly route reflection is not the only motivation for this work.
The justification only related to RRs seems gratuitous. Just a nit...

105 This document defines the R-bit functionality equivalent for OSPFv2
106 defined in [RFC2328] by introducing a new router-LSA bit known as the
107 "H-bit". This document updates appendix A.4.2 of RFC 2328.

[nit] s/OSPFv2 defined in [RFC2328]/OSPFv2 [RFC2328] It sounds as if "the
R-bit functionality equivalent for OSPFv2" is already in rfc2328.

[major] Please be specific about what the Update is.

...
117 3. H-bit Support

119 This document defines a new router-LSA bit known as the Host Bit or
120 the H-bit. An OSPFv2 router advertising a router-LSA with the H-bit
121 set indicates to other OSPFv2 routers in the area supporting the
122 functionality that it MUST NOT be used as a transit router. The bit
123 value usage of the H-bit is reversed from the R-bit defined in OSPFv3
124 [RFC5340] to support backward compatibility. The modified OSPFv2
125 router-LSA format is:

[minor] "...MUST NOT be used as a transit router" Put a forward reference
to §4.

[nit] The text keeps making reference to the R-bit. Even though there is a
relationship, the H-bit is an independent feature. IOW, I don't think
there's a need to explain the relationship to OSPFv3.

[minor] On the same topic: The comparison to OSPFv3 is made and the
"reverse" bit setting is justified "to support backward compatibility", but
that is not explained anywhere. I was hoping that §5 (Auto Discovery and
Backward Compatibility) would say something, but it doesn't.

127 0 1 2 3
128 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
130 | LS age | Options | 1 |
131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
132 | Link State ID |
133 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
134 | Advertising Router |
135 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
136 | LS sequence number |
137 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
138 | LS checksum | length |
139 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
140 |H|0|0|N|W|V|E|B| 0 | # links |
141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
142 | Link ID |
143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
144 | Link Data |
145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
146 | Type | # TOS | metric |
147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
148 | ... |
149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
150 | TOS | 0 | TOS metric |
151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
152 | Link ID |
153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
154 | Link Data |
155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
156 | ... |

158 bit H
159 When set, an OSPFv2 router is a non-transit router and is
160 incapable of forwarding transit traffic.

[nit] Please label the figure: Figure 1...

[minor] Even though it seems obvious from the figure, please be explicit in
saying that the H-bit is the first bit (or however that bit is
identified)...

162 When the H-bit is set, an OSPFv2 router is a non-transit router and
163 should not be used to forward transit traffic. In this mode, the
164 other OSPFv2 routers in the area SHOULD NOT use the originating
165 OSPFv2 router for transit traffic, but MAY use the OSPFv2 router for
166 local traffic destined to that OSPFv2 router.

[minor] The first/second sentences seem redundant: "should not be used to
forward transit traffic...SHOULD NOT use the originating OSPFv2 router for
transit traffic".

[major] When would the non-transit router be used for transit? IOW, why
use "SHOULD NOT" and not "MUST NOT"?

[major] "MAY use the OSPFv2 router for local traffic destined to that
OSPFv2 router" I'm not sure what behavior is being specified here. The
text sounds as if it was optional to even consider the router as a traffic
destination. Is that the intent? Why? What would make a network operator
decide one way or the other?

168 An OSPFv2 router originating a router-LSA with the H-bit set SHOULD
169 advertise all its non-local router links with a link cost of
170 MaxLinkMetric as defined in Section 3 of [RFC6987]. This is to
171 increase the applicability of the H-bit to partial deployments where
172 it is the responsibility of the operator to ensure that OSPFv2
173 routers not supporting the H-bit do not install routes causing
174 routing loops.

[major] When would a router not advertise MaxLinkMetric? IOW, why use
SHOULD and not MUST?

[major] What are "non-local router links"? I always thought of links to be
local to the router...what am I missing?

[nit] s/advertise all its non-local router links with a link cost of
MaxLinkMetric as defined in Section 3 of [RFC6987]/advertise all its
non-local router links with a link cost of MaxLinkMetric [RFC6987]

176 When the H-bit is set, IPv4 prefixes associated with local interfaces
177 in other areas MAY be advertised in summary LSAs. Non-local IPv4
178 prefixes, e.g., those advertised by other routers and installed
179 during the SPF computation, MAY be advertised in summary-LSAs if
180 configured by policy. Likewise, when the H-bit is set, only IPv4
181 prefixes associated with local interfaces MAY be advertised in AS-
182 external LSAs. Non-local IPv4 prefixes, e.g., those exported from
183 other routing protocols, MUST NOT be advertised in AS-external-LSAs.
184 Finally, when the H-bit is set, an Area Border Router (ABR) MUST
185 advertise a consistent H-bit setting in its self-originated router-
186 LSAs for all attached areas.

[minor] Some of the behavior specified in this paragraph may be non
intuitive -- for example: "When the H-bit is set, IPv4 prefixes associated
with local interfaces in other areas MAY be advertised in summary LSAs."
During normal operation (aka rfc2328), these prefixes are always
advertised (assuming normal areas, etc.)...and given that these are local
to the router, it can be argued that one is not using the router as
transit...on the other hand, going to a different area can be interpreted
as transit. In either case, it would be nice if more was said about the
optional nature of including these prefixes in the summary LSA. What are
the operational considerations?

[minor] The same comment for "prefixes associated with local interfaces MAY
be advertised in AS-external LSAs".

[major] "Non-local IPv4 prefixes...MAY be advertised in summary-LSAs if
configured by policy." Doesn't advertising result in the router being
transit? Doesn't it defeats the purpose of setting the H-bit? But there
may be operational reasons to do so -- e.g. if the router is the only ABR..

---

From: Keyur Patel <[email-masked]>
Date: Tue, 12 Feb 2019 22:02:43 +0000

Hi Alvaro,

Apologies for the delay. We will go thru the comments and get back to you.

Regards,
Keyur

From: Alvaro Retana <[email-masked]>
Date: Tuesday, February 12, 2019 at 1:26 PM
To: Padmadevi Pillay Esnault <[email-masked]>, "[email-masked]" <[email-masked]>
Cc: Yingzhen Qu <[email-masked]>, "[email-masked]" <[email-masked]>, "[email-masked]" <[email-masked]>, "Acee Lindem (acee)" <[email-masked]>
Subject: Re: AD Review of draft-ietf-ospf-ospfv2-hbit-06
Resent-From: <[email-masked]>
Resent-To: <[email-masked]>, <[email-masked]>, <[email-masked]>, <[email-masked]>
Resent-Date: Tuesday, February 12, 2019 at 1:26 PM

Ping!

Thanks!

Alvaro.

On December 17, 2018 at 8:22:25 AM, Acee Lindem (acee) ([email-masked]<mailto:[email-masked]>) wrote:
Hi Padma,
Is the updated draft coming soon?
Thanks,
Acee

On 11/28/18, 2:31 PM, "Padmadevi Pillay Esnault" <[email-masked]<mailto:[email-masked]>> wrote:

Dear Alvaro

Thanks

On 11/28/18, 7:53 AM, "Alvaro Retana" <[email-masked]<mailto:[email-masked]>> wrote:

Dear authors:

Thanks!

Alvaro.

...

14 Abstract

...
42 Copyright Notice

...
85 1. Introduction

...
117 3. H-bit Support

[minor] On the same topic: The comparison to OSPFv3 is made and the
"reverse" bit setting is justified "to support backward compatibility", but
that is not explained anywhere. I was hoping that §5 (Auto Discovery and
Backward Compatibility) would say something, but it doesn't