Re: [Lsr] Opsdir last call review of draft-ietf-ospf-ospfv2-hbit-10

Padma Pillay-Esnault <> Fri, 08 November 2019 01:08 UTC

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From: Padma Pillay-Esnault <>
Date: Thu, 7 Nov 2019 17:07:54 -0800
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To: Tim Chown <>
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Subject: Re: [Lsr] Opsdir last call review of draft-ietf-ospf-ospfv2-hbit-10
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Hi Tim

Thank you for your review and comments.

See below PPE.

On Thu, Nov 7, 2019 at 2:22 PM Tim Chown via Datatracker <>

> Reviewer: Tim Chown
> Review result: Has Nits
> I have reviewed this document as part of the Operational directorate's
> ongoing
> effort to review all IETF documents being processed by the IESG.  These
> comments were written with the intent of improving the operational aspects
> of
> the IETF drafts. Comments that are not addressed in last call may be
> included
> in AD reviews during the IESG review.  Document editors and WG chairs
> should
> treat these comments just like any other last call comments.
> The document describes a mechanism by which a node running OSPFv2 can repel
> transit traffic if it is on the shortest path (and an alternative path
> exists -
> though this is not wholly clear in the document). It defines a Host-bit
> (H-bit)
> that allows the router to advertise that it is not a transit router, and it
> describes the changes needed to support the H-bit within a domain, and
> mitigations against potential routing loops.
> General comments:
> Should the document also state that it updates RFC 2328?
PPE> No. This has been discussed previously during the AD review.
This feature is an optional feature and RFC2328 does not require it for
normal operations.

> I think the document could be clearer on the behaviour when the H-bit and
> MaxLinkMetric are used when there is only one path available, i.e. there
> is no
> redundant / alternative path.  Section 4 of RFC 6987 implies that if there
> is
> only one path the router can still be used as a transit router, by the
> nature
> of the definition of MaxLinkMetric.  The document has 3 or 4 places where
> it
> hints at behaviour, but I think it could be more explicit.
PPE>   This feature goes one step further than RFC 6987 which is a best
effort at stopping transit traffic.
We believe that the behavior is clear that a "host router" is NOT used for
transit  traffic regardless whether it is the last resort path or not.
Please note the CURRENT version does not restrict the feature on a specific
number of paths (last resort or not) or metric value (MaxlinkMetric or not)
or make any assumption in that way.

However, I proposed to add this text in an earlier thread  to make it even
more explicit.

This document describes the Host-bit (H-bit) functionality that prevents
other OSPFv2 routers from using the host router for transit traffic in
OSPFv2 routing domains.

This document describes the Host-bit (H-bit) functionality that prevents
other OSPFv2 routers from using the host router by excluding it in path
calculations for transit traffic in OSPFv2 routing domains.

> It may be worth explicitly stating that OSPFv3 is not mentioned due to it
> having an R-bit defined for indicating whether a node/router can be used
> for
> transit traffic (see Sections 2.7 and A.2 of RFC 5340).
PPE> There was an earlier discussions regarding mentioning the OSPFv3
functionality and eventually these references were removed in subsequent
versions of the H-bit draft.
The R-bit is not exactly the same as H-bit, even though both are used for
the similar functionality, they rely on different mechanisms in the

> The reasons given in Section 1 for the need for the H-bit are different to
> those given in Section 1 of RFC 6987 for the capability.  Should these be
> more
> consistent?   Also, the document later mentions “a router being gracefully
> isolated” as a reason, but this is not mentioned in Section 1.
PPE>  We believe that this the document covers this case in bullet 1 and
bullet 3 in section1.


1.  To isolate a router to avoid blackhole scenarios when there is a
       reload and possible long reconvergence times.
3.  Overloaded routers could use such a capability to temporarily
       repel traffic until they stabilize.

To make it even more explicit:

1. To gracefully isolate a router to avoid blackhole scenarios when there
is a
       reload and possible long reconvergence times.

Let me know if this addresses all your comments


> In the abstract:
> Change
> “This document defines a bit (Host-bit)”
> to
> “This document defines a Host bit (H-bit)”
> for consistency
> And “is a non-transit router.”” - remove the spurious “.
> Section 8:
> Where it says “beyond those already known in OSPF”, say OSPFv2.