Subject: Gating for MaxAge LSA in ospfv3

From: Misha Dovek <[email-masked]>
Date: Thu, 17 Oct 2002 23:39:35 +0530

Hi,
Do we apply any gating for MaxAge LSAs in OSPF v3. There is this
MinLSAInterval timer which is applied to all LSA originations in OSPF v2.
Does this hold true in OSPF v3 also? And specially for the Max Age LSAs.

Dont we have this concept of "Bad news fast .. Good news slow" here.

Misha.

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From: Acee Lindem <[email-masked]>
Date: Fri, 18 Oct 2002 01:46:03 -0400

Hello Misha,

> Does this hold true in OSPF v3 also? And specially for the Max Age LSAs.

The MinLSAInterval delay is retained from OSPF v2.

> Dont we have this concept of "Bad news fast .. Good news slow" here.

With respect to LSA origination, MinLSAInterval is applied
equally to re-originations and purging.

--
Acee

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From: Yasuhiro Ohara <[email-masked]>
Date: Fri, 18 Oct 2002 19:53:00 +0900

acee> > Do we apply any gating for MaxAge LSAs in OSPF v3. There is this
acee> > MinLSAInterval timer which is applied to all LSA originations in OSPF v2.
acee> > Does this hold true in OSPF v3 also? And specially for the Max Age LSAs.
acee>
acee> The MinLSAInterval delay is retained from OSPF v2.
acee>
acee> > Dont we have this concept of "Bad news fast .. Good news slow" here.
acee>
acee> With respect to LSA origination, MinLSAInterval is applied
acee> equally to re-originations and purging.

Actually, RFC 2328 is ambiguous about it.
Because it does not mention about it, I think that MinLSInterval
should not be applied to premature agings, as it lengthen the
convergence time ... I think we should take the concept "Bad new fast".

regards,
yasu

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From: Acee Lindem <[email-masked]>
Date: Fri, 18 Oct 2002 10:04:26 -0400

> Actually, RFC 2328 is ambiguous about it.

Hello Yasu,

RFC 2328 does say that say a number of times that the "fundamental mechanisms
of  OSPF (flooding, DR election, area support, etc) remain unchanged".

--
Acee

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From: Yasuhiro Ohara <[email-masked]>
Date: Fri, 18 Oct 2002 23:10:43 +0900

acee> > acee> > Do we apply any gating for MaxAge LSAs in OSPF v3. There is this
acee> > acee> > MinLSAInterval timer which is applied to all LSA originations in OSPF v2.
acee> > acee> > Does this hold true in OSPF v3 also? And specially for the Max Age LSAs.
acee> > acee>
acee> > acee> The MinLSAInterval delay is retained from OSPF v2.
acee> > acee>
acee> > acee> > Dont we have this concept of "Bad news fast .. Good news slow" here.
acee> > acee>
acee> > acee> With respect to LSA origination, MinLSAInterval is applied
acee> > acee> equally to re-originations and purging.
acee> >
acee> > Actually, RFC 2328 is ambiguous about it.
acee>
acee> Hello Yasu,
acee>
acee> RFC 2328 does say that say a number of times that the "fundamental mechanisms
acee> of  OSPF (flooding, DR election, area support, etc) remain unchanged".
acee>
acee> > Because it does not mention about it, I think that MinLSInterval
acee> > should not be applied to premature agings, as it lengthen the
acee> > convergence time ... I think we should take the concept "Bad new fast".

"remain unchanged" from what ? is that sentence from RFC *2740*, isn't
it ?

What I'm talking about is not the difference between OSPFv2 and
OSPFv3.

I said "original OSPFv2 (and hence also OSPFv3) specification is
ambiguous about whether to apply MinLSInterval when purging of LSA
(i.e. premature aging)".

Am I missing something ?

regards,
yasu

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From: Acee Lindem <[email-masked]>
Date: Fri, 18 Oct 2002 11:49:15 -0400

> What I'm talking about is not the difference between OSPFv2 and

Sorry, I misread your post. I'll use my morning excuse of not having
drunken enough coffee :-)

> ambiguous about whether to apply MinLSInterval when purging of LSA

I don't think there is ambiguity in RFC 2328.

MinLSInterval is defined as the minimum time between distinct originations
of any particular LSA. When you purge an LSA you are definitely re-originating
it with a new sequence number and MaxAge.

I'm not advocating violating the specification. However is an implementation
does flood MaxAge LSAs immediatedly, it better make damn sure that the initial
origination is delayed MinLSInterval seconds after a purge. In other words,
once an LSA is purged state must be retained to assure that a new origination
is at least MinLSInterval seconds later. I'm pretty sure there are a lot of
implementations that do not retain state after an LSA is purged and
successfully flooded.

Thanks,
Acee

--
Acee

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From: Sina Mirtorabi <[email-masked]>
Date: Fri, 18 Oct 2002 13:46:54 -0700

Yasu,

> convergence time ... I think we should take the concept "Bad new fast".

although MinLSInterval is an architectural constant, implementations could
make this interval configurable ( with backoff algo ) in order to speed up
the convergence.

now regarding Maxage LSA, it should be noted that although you could make
the bad news faster ( say by having a different interval for maxage LSA )
you will not always benefit from it ( type 1 and 2 LSA ) this is because
when an adj is broken or a prefix is removed you will simply originate a new
version of LSA by making the corresponding change in the content so having a
shorter interval for maxage LSA will not help there ...

Sina

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From: Yasuhiro Ohara <[email-masked]>
Date: Mon, 21 Oct 2002 07:15:15 +0900

acee> > I said "original OSPFv2 (and hence also OSPFv3) specification is
acee> > ambiguous about whether to apply MinLSInterval when purging of LSA
acee> > (i.e. premature aging)".
acee>
acee> I don't think there is ambiguity in RFC 2328.
acee>
acee> MinLSInterval is defined as the minimum time between distinct
acee> originations of any particular LSA. When you purge an LSA you
acee> are definitely re-originating it with a new sequence number and
acee> MaxAge.

I find that you interpret the sentence "while leaving its LS sequence
number alone" (RFC2328 14.1) as "with a new sequence number".
And it is not described clearly that "premature aging" is
"re-originating of LSA". Actually I didn't recognize that the sequence
number of LSA going to be premature aged is (in most case) a new one
from the view of the premature aging router itself,
though I am working on OSPF a few years ...
 ................. so it's ambiguous ;p)

I agree rest of acee's and all of sina's.

Just my excuse,
yasu

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From: Acee Lindem <[email-masked]>
Date: Sun, 20 Oct 2002 23:06:34 -0400

Yasu,

I just looked at John Moy's public domain implementation
and it doesn't apply the MinLSInterval to prematurely aged LSAs.
So your interpretation is correct - premature LSA aging doesn't count
as a reorigination.

Thanks,
Acee

--
Acee

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From: Manav Bhatia <[email-masked]>
Date: Mon, 21 Oct 2002 08:41:37 +0530

Sina,
We can definitely benefit from originating MaxAge LSA without waiting for
the MinLSInterval.

Following are some scenarios when this might be useful.

1> A router that was formerly a DR for a network, but is now no longer,
needs to flush the network-LSA that it had previously originated.  I see no
point in waiting for MinLSInterval.

3> If a router is advertising a summary-LSA/AS-External LSA for a
destination which becomes unreachable, it needs to flush that LSA from the
routing domain by setting its age to MaxAge and reflooding. Why should I
wait for 5 secs to do that?

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From: Sina Mirtorabi <[email-masked]>
Date: Mon, 21 Oct 2002 03:25:30 -0700

Manav,

> -----Original Message-----
> From: Mailing List [mailto:[email-masked]]On Behalf Of Manav
> Bhatia
> Sent: Sunday, October 20, 2002 8:12 PM
> To: [email-masked]

what you call _benefit_ ? we were talking about _fast convergence_  and
announcing bad news fast

> point in waiting for MinLSInterval.

I do not see how convergence is faster if the old DR Maxage its old network
LSA faster than MinLSInterval ?
even if the router is unable to maxage ( it is down ) it will remain for
maxage time in the database BUT the convergence is not impacted

> wait for 5 secs to do that?

if you read my e-mail one more time ;-) you will see that I mentioned for
"type 1 and type 2".
for summary / external, sure you could maxage right away ...
also in the case of summary origination the SPF needs to be scheduled in
order to originate / maxage summary LSA therefore your LSA will be anyway
delayed ( throttled ) so there might not be a need for extra interval time

Sina