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Date: Sun, 16 Aug 2015 12:26:58 +0900
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From: Nobo Akiya <nobo.akiya.dev@gmail.com>
To: Gregory Mirsky <gregory.mirsky@ericsson.com>
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Archived-At: <http://mailarchive.ietf.org/arch/msg/mpls/bzs_dNvozpiv7_z9O1BFXpmkvUI>
Cc: Ross Callon <rcallon@juniper.net>, mpls <mpls@ietf.org>,
 "draft-mirsky-mpls-bfd-directed@tools.ietf.org"
 <draft-mirsky-mpls-bfd-directed@tools.ietf.org>
Subject: Re: [mpls] Review of draft-mirsky-mpls-bfd-directed-03
Precedence: list

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Hi March, Greg,

My apologies for very delayed response.

Please see in-line with [NOBO].

Note I've snipped out sections that I accept your response.


> > Section 2
> >
> > o if reverse direction is in Down state, the head-end node would not
> >    receive indication of forward direction failure from its egress
> >    peer.
> >
> > [NOBO] I found above to be slightly unclear in 2 aspects.
> >
> > Since this section is describing the limitations of using BFD on an
> > unidirectional explicitly routed path, what does "if reverse direction
> is in Down state" mean?
> >
> > Additionally, "would not receive indication of forward direction
> > failure from its egress peer" is a bit cryptic. If the egress peer
> > detected that forward direction failed (e.g., BFD session timed out),
> > then the egress peer will send few BFD control packets with DOWN
> > state, IP routed. Thus the ingress peer will notice the problem of the
> forward direction.
> >
> > Readers can likely benefit from having this bullet point better
> clarified.
> >
>
> GIM=E2=89=AB Would the following wording be more deterministic:
>    o  failure detection on the reverse path cannot reliably be
>       interpreted as bi-directional failure and thus trigger, for
>       example, protection switchover of the forward direction;
>
>    o  if a failure of the reverse path being ignored, the ingress node
>       would not receive indication of forward direction failure from its
>       egress peer.
>
>

[NOBO] The second bullet may create more confusion. Can we keep just the
first bullet and add a bit of clarifications as below?

* a failure detection on the reverse path cannot reliably be
  interpreted as bi-directional failure and thus trigger, for
  example, protection switchover of the forward direction.
  When the BFD session on the egress node declares a failure
  (i.e., forward direction failure), the failure may or may not
  reach the ingress node. Therefore, the BFD session on the
  ingress node declaring failure may be a result of just the
  reverse path failure or both forward and reverse paths
  failures.

Regards,
Nobo

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<div dir=3D"ltr">Hi March, Greg,<div><br></div><div>My apologies for very d=
elayed response.</div><div><br></div><div>Please see in-line with [NOBO].</=
div><div><br></div><div>Note I&#39;ve snipped out sections that I accept yo=
ur response.</div><div><br><div class=3D"gmail_extra"><div class=3D"gmail_q=
uote"><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-l=
eft:1px #ccc solid;padding-left:1ex"><div><font face=3D"Calibri" size=3D"2"=
><span style=3D"font-size:11pt"><div><br></div><div><div class=3D"h5">
<div>&gt; Section 2</div>
<div>&gt; </div>
<div>&gt; o if reverse direction is in Down state, the head-end node would =
not</div>
<div>&gt; =C2=A0 =C2=A0receive indication of forward direction failure from=
 its egress</div>
<div>&gt; =C2=A0 =C2=A0peer.</div>
<div>&gt; </div>
<div>&gt; [NOBO] I found above to be slightly unclear in 2 aspects.</div>
<div>&gt; </div>
<div>&gt; Since this section is describing the limitations of using BFD on =
an </div>
<div>&gt; unidirectional explicitly routed path, what does &quot;if reverse=
 direction is in Down state&quot; mean?</div>
<div>&gt; </div>
<div>&gt; Additionally, &quot;would not receive indication of forward direc=
tion </div>
<div>&gt; failure from its egress peer&quot; is a bit cryptic. If the egres=
s peer </div>
<div>&gt; detected that forward direction failed (e.g., BFD session timed o=
ut), </div>
<div>&gt; then the egress peer will send few BFD control packets with DOWN =
</div>
<div>&gt; state, IP routed. Thus the ingress peer will notice the problem o=
f the forward direction.</div>
<div>&gt; </div>
<div>&gt; Readers can likely benefit from having this bullet point better c=
larified.</div>
<div>&gt; </div>
<div>=C2=A0</div>
</div></div><div>GIM<font face=3D"Cambria Math">=E2=89=AB</font> Would the =
following wording be more deterministic:</div>
<div>=C2=A0=C2=A0 o=C2=A0 failure detection on the reverse path cannot reli=
ably be</div>
<div>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 interpreted as bi-directional failure a=
nd thus trigger, for</div>
<div>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 example, protection switchover of the f=
orward direction;</div>
<div>=C2=A0</div>
<div>=C2=A0=C2=A0 o=C2=A0 if a failure of the reverse path being ignored, t=
he ingress node</div><span class=3D"">
<div>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 would not receive indication of forward=
 direction failure from its</div>
<div>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 egress peer.</div>
<div>=C2=A0</div></span></span></font></div></blockquote><div><br></div><di=
v>[NOBO] The second bullet may create more confusion. Can we keep just the =
first bullet and add a bit of clarifications as below?</div><div><br></div>=
<div>* a failure detection on the reverse path cannot reliably be</div><div=
>=C2=A0 interpreted as bi-directional failure and thus trigger, for</div><d=
iv>=C2=A0 example, protection switchover of the forward direction.</div><di=
v>=C2=A0 When the BFD session on the egress node declares a failure<br></di=
v><div>=C2=A0 (i.e., forward direction failure), the failure may or may not=
</div><div>=C2=A0 reach the ingress node. Therefore, the BFD session on the=
</div><div>=C2=A0 ingress node declaring failure may be a result of just th=
e</div><div>=C2=A0 reverse path failure or both forward and reverse paths</=
div><div>=C2=A0 failures.</div><div><br></div><div>Regards,</div><div>Nobo=
=C2=A0</div></div></div></div></div>

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