Re: OSPF and LDP Intricacies

Still i m not convinced about the Flooding convergence within an area in
OSPF. I understand that Link state Request s not required always. But LSDB
flushes it when max age ages out.

Now what is the use of this DR/BDR logic.

When DRother sends LSA to 224.0.0.6 . ( ie DROthers Type 1 LSA goes to
224.0.0.6 ) to DR and BDR. And DR again send the Type 2 LSA to all routers
224.0.0.5 which is again sent to all routers.

Why not DRother itself can send its update to all. I know that it avoids
n(n-1)/2 adjacencies in OSPF. But i still dont see any significant
advantage in DR/BDR logic.

Can someone throw some light on this.

On Tue, Aug 6, 2013 at 2:17 PM, HEMANTH RAJ <hemanthrj_at_gmail.com> wrote:

> LSR is required not always. It depends on the topology.
> If it is a flat back to back connected topology like this
>
> R1-------R2-------R3--------R4------R5
>
> Everyone doesnt know about each other by any other link . In this case,
> DBD sends the brief databases of each other and LSR is sent by the neighbor
> to get the updates.
>
> Lets consider a ring topology where R2 is connected to R4 via another
> link and in that case, R2 exchanges DBDs with R4 and in that case, Its LSA
> will be sent to R3 and R3 would have relayed the LSAs to R4 and also R3
> generated its own LSUs to R4 .
>
> So in this case R4 knows about R2's connected links previously itself and
> he doesnt explicitly ask for certain LSUs
>
> So OSPF is designed to support all topologies and there is a design
> constraint in itself when you have inter area logic running.
>
>
> LDP by default uses IGP has its default loop prevention mechanism . OSPF
> and ISIS LFA. Even LDP LFA ( Loop Free Alternates ) is available for loop
> free detection logic.
>
> I havent seen Path Vector and Hop Count TLV previously.
>
> Merging two LSPs (going to the same destination) reduces the number of
> labels being used in the network. However it makes it impossible to
> differentiate between traffic common from two different sources before the
> merging happened. To simplify things in transport networks, LSP merge was
> also disabled.
>
>
>
>
>
> On Mon, Aug 5, 2013 at 10:33 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:
>
>> I think you may be wrong here, just to be symmetrical :)
>>
>> OSPF does not "flush" anything. The only way to get rid of DB data is by
>> means of MAXAGE timeout.
>>
>> Also, keep in mind that even when a link down, routers may still be
>> connected via some alternate route, and so the DB might be up to date
>> already when the link comes back up (Minus the two LSAs that relate to
>> the link being brought up).
>>
>> -Carlos
>>
>> routingfreak @ 05/08/2013 13:53 -0300 dixit:
>> > Hi Carlos
>> >
>> > I think u may be wrong here
>> >
>> > R1-----------R2--------------R3----------R4
>> >
>> > When link between R2 and R3 fails , so watever R3 gave to R2 will be
>> > flushed out, and when R3 forms neighorship with R2 again, R2 will
>> > request for all the updates, for wat R3 is connected.
>> >
>> > So where Link State Request helps here.. Why not R3 can send all the
>> > LSUs directly.
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > On Mon, Aug 5, 2013 at 8:25 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar
>> > <mailto:tron_at_huapi.ba.ar>> wrote:
>> >
>> > First part: router A and B from some area may get disconnected for
>> some
>> > time, and the world goes on. When they reconnect (link up) part of
>> the
>> > DB could be up to date and part may be not. Exchanging just the DBD
>> > enables a more efficient update, just the needed data is sent.
>> >
>> > Makes sense ?
>> > -Carlos
>> >
>> > routingfreak @ 05/08/2013 11:37 -0300 dixit:
>> > > Hi all
>> > >
>> > > I have certain questions on OSPF .
>> > >
>> > > 1. Why do we require Link State Request Packet. I mean as per Link
>> > State
>> > > Routing Protocol, ur entire database has to be synchronised, then
>> you
>> > > should not request someone to get something, instead the neighbor
>> > should
>> > > give you entire LSUs to you
>> > >
>> > > Why they have designed Link State Request packet in OSPF.
>> > > Anyhow the neighbor will request for all the LSAs from the DBD,
>> > then why do
>> > > they have Link State Request Packet in OSPF
>> > >
>> > > In LDP, There is a Loop Detection Mechanism which includes Hop
>> > Count TLV
>> > > and Path Vector TLV, Can someone throw some light on how these two
>> > things
>> > > are utilised,
>> > > I have read the RFC and this is wat it says
>> > >
>> > > Loop Detection is a configurable option that provides a mechanism
>> for
>> > > finding looping LSPs and for preventing Label Request messages
>> > from looping
>> > > in the presence of non-merge capable LSRs.
>> > >
>> > > Can someone explain me wat is called as Non-Merged LSRs
>> > >
>> > >
>> >
>> > --
>> > Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
>> > LW7 EQI Argentina
>> >
>> >
>> >
>> >
>> > --
>> > Regards
>> > Routing Freak CCIE#35889 (SPv3)
>>
>> --
>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>
>>
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>>
>
>
> --
>
> Regards
> Hemanth Raj
> CCIE#28593 (R&S)
>
>

-- 
Regards
Routing Freak CCIE#35889 (SPv3)
Blogs and organic groups at http://www.ccie.net