Re: LSDB Overflow Limitation?

[Acee Lindem <[e-mail]>]

Charles, 

You can choose to implement RFC 1765 but you cannot
advertise the fact that your router is in overflow state in a 
field in OSPF hello packets. First of all, there are no unused fields
or option bits and even if there were we wouldn't want to 
allocate them for this purpose. 

There are free bits in the router LSA bits but personally
I don't see a strong requirement to advertise entry or
exit from overflow state. 

I don't agree with everything that has been stated in this
mail thread but I do agree that RFC 1765 dates to a
time when low-end routers had very limited memory. Again, you
can choose to implement this RFC. However, I personally 
think a local knob specifying the upper limit on the number
of external routes that you'll advertise is more useful. 

Thanks,
Acee 
  ----- Original Message ----- 
  From: Charles Liang 
  To: [e-mail] 
  Sent: Thursday, July 08, 2004 2:17 PM
  Subject: Re: LSDB Overflow Limitation?


  Mitchell,

  It sounds like we prefer to pre-allocate the resource,
  rather than process the overflow conditions?!
  I also belive that the number has to be matched with
  the limit counts, and pre-allocating the resource
  should be a pratical solution.

  What I concerned is the exception? from RFC1765.
  If we have to implement this feature, we'd like
  to make sure the implementation works for all
  the possible cases.  Otherwise, shouldn't we prefer
  to announce that my OSPF router will NEVER fall
  into LSDB overflow state.

  Therefore, I'm wondering that
  (1) Is my realization about RFC1765 correct?
  (2) Will the problem that I described happen?
  (3) Is there any side effect if I use a reserved
  and unused field in HELLO-Option?
  (4) Is it worth of implemeting RFC1765?

  Charles 

  Erblichs <[e-mail]>
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  Charles,


        The number really has to do with
        the number of non default AS-external
        LSAs.

        These are believed to represent the
        maj of LSAs in the LSDB.

        In my experience, this only occurs
        with memory limited routers and
        routers within the same area are
        normally set to the same values.

        Realize that in memory limited routers,
        you are pre-allocating enough memory
        to cover the limit and that memory will
        not be available for other functions.

        Mitchell Erblich
        -----------------

  > Charles Yi-tung Liang wrote:
  >
  > Hi,
  >
  > Here below is my understanding from RFC1765
  > to process lsdb overflow condition.
  >
  > Goal: Make every OSPF router to be awared of
  > the overflow state, and thus reduce the number
  > of lsdb.  That's why we required all the OSPF
  > routers setup the same limited lsdb threshold.
  >
  > Process: As mentioned in RFC1765.
  >
  > Limitation?/Problem?:
  > Since the new LSA update from someone triggers
  > overflow state (when currentLSACount == limitedLSACount)
  > via flooding, there is chance that certain OSPF router
  > will miss such a critial event.  Moreover, the following
  > premature actions may make someone else believing
  > there is not yet an overflow event.  Why don't we just set
  > up a beacon bit to notify everyone?  For example,
  > using a reserved filed in HELLO-Option to notify
  > overflow.  Afterward, when all the neighbors acked
  > with overflow beacon-bit, reset (clear) such a bit.
  >
  > Could anyone help clearing my doubt?
  >
  > BTW, if the overflow process needs to be applied
  > to Inter-AS LSAs (Area-Oriented), what kind of
  > LSA is suggested to be prematured?  Can I leave
  > RTRLink, NetLink, and ASSummary alone?
  > Will OSPF WG include the overflow process as
  > a part of OSPFv3?
  >
  > Thanks in advance.
  >
  > Charles