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List: ms-ospf
Subject: Re: [Lsr] draft-ietf-isis-segment-routing-extensions
From: "Les Ginsberg (ginsberg)" <ginsberg () cisco ! com>
Date: 2019-04-03 15:01:18
Message-ID: BYAPR11MB3638366B5EEF1131EA603D4DC1570 () BYAPR11MB3638 ! namprd11 ! prod ! outlook ! com
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Mobashshera -
Thanx for your interest.
While there is nothing wrong with advertising Algo 0 first, the benefits of=
doing so are minimal. This is because when SR algorithm sub-TLV is receive=
d all the algorithms advertised need to be parsed by the receiver. If your =
argument is that having algorithm 0 advertised first would speed detection =
of an invalid sub-TLV my comment is that you are optimizing for the error c=
ase - which practically speaking should never occur.
In any case it is too late to make advertisement of Algo 0 first a requirem=
ent as this would not be backwards compatible with existing implementations=
..
Les
From: Mobashshera Rasool <Mobashshera.Rasool@huawei.com>
Sent: Wednesday, April 03, 2019 6:07 AM
To: draft-ietf-isis-segment-routing-extensions@ietf.org; lsr@ietf.org
Subject: draft-ietf-isis-segment-routing-extensions
Dear Authors,
I have a suggestion. Have a look :)
As per section 3.2. SR-Algorithm Sub-TLV of this draft, a router must adv=
ertise algorithm 0 if it advertises SR Algorithm Sub TLV.
[cid:image001.png@01D4E9F3.6A0934E0]
Therefore if a router does not advertises algorithm 0 in this sub TLV, then=
we MUST discard the SUB TLV.
Suggestion: Algorithm 0 can be added as the first Algorithm in the below su=
b-tlv (Check if we can make this as must condition in the draft).
So that we can avoid parsing and searching for Algorithm 0 in the complete =
sub-tlv, and can decide to discard the sub TLV by reading only the first by=
te.
[cid:image002.png@01D4E9F3.6A0934E0]
:)
Regards,
Mobashshera Rasool
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<p class="MsoNormal"><span style="color:#1F497D">Mobashshera \
–<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><span \
style="color:#1F497D">Thanx for your interest.<o:p></o:p></span></p> <p \
class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span style="color:#1F497D">While there is nothing wrong with \
advertising Algo 0 first, the benefits of doing so are minimal. This is because when \
SR algorithm sub-TLV is received all the algorithms advertised need to be parsed by \
the receiver. If your argument is that having algorithm 0 advertised first would \
speed detection of an invalid sub-TLV my comment is that you are optimizing for the \
error case – which practically speaking should never \
occur.<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><span \
style="color:#1F497D">In any case it is too late to make advertisement of Algo 0 \
first a requirement as this would not be backwards compatible with existing \
implementations.<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><span \
style="color:#1F497D"> Les<o:p></o:p></span></p> <p \
class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p> <div \
style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt"> <div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> Mobashshera Rasool \
<Mobashshera.Rasool@huawei.com> <br>
<b>Sent:</b> Wednesday, April 03, 2019 6:07 AM<br>
<b>To:</b> draft-ietf-isis-segment-routing-extensions@ietf.org; lsr@ietf.org<br>
<b>Subject:</b> draft-ietf-isis-segment-routing-extensions <o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dear Authors,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have a suggestion. Have a look <span \
style="font-family:Wingdings"> J</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As per section <b>3.2.</b> <b>SR-Algorithm Sub-TLV</b> of \
this draft, a router <b>must</b> advertise algorithm 0 if it advertises SR \
Algorithm Sub TLV.<o:p></o:p></p> <p class="MsoNormal"><img width="655" height="331" \
style="width:6.8229in;height:3.4479in" id="Picture_x0020_11" \
src="cid:image001.png@01D4E9F3.6A0934E0"><o:p></o:p></p> <p \
class="MsoNormal"><o:p> </o:p></p> <p \
class="MsoNormal"><b><o:p> </o:p></b></p> <p class="MsoNormal">Therefore if a \
router does not advertises <b>algorithm 0</b> in this sub TLV, then we MUST discard \
the SUB TLV.<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b><span style="color:#C00000">Suggestion:</span></b><span \
style="color:#C00000"> Algorithm 0 can be added as the first Algorithm in the below \
sub-tlv (Check if we can make this as must condition in the draft). \
<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="color:#C00000"><o:p> </o:p></span></p> <p class="MsoNormal"><span \
style="color:#C00000">So that we can avoid parsing and searching for Algorithm 0 in \
the complete sub-tlv, and can decide to discard the sub TLV by reading only the first \
byte. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#C00000"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#C00000"><img width="669" height="259" \
style="width:6.9687in;height:2.6979in" id="Picture_x0020_17" \
src="cid:image002.png@01D4E9F3.6A0934E0"><o:p></o:p></span></p> <p \
class="MsoNormal"><span style="color:#C00000"><o:p> </o:p></span></p> <p \
class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal"><span \
style="font-family:Wingdings;color:#C00000">J</span><span \
style="color:#C00000"><o:p></o:p></span></p> <p \
class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal"><span \
style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span \
style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">Mobashshera \
Rasool<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:12.0pt;font-family:"Times New \
Roman",serif"><o:p> </o:p></span></p> </div>
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["image001.png" (image/png)]
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