Subject: [OSPF] Question on flodding scope in draft-ietf-ospf-ospfv3-update-17.txt

From: "Adrian Farrel" <[email-masked]>
Date: Wed, 10 Oct 2007 14:30:57 +0100

Hi,

In section 2.3...

   o  AS scope.  LSA is flooded throughout the routing domain.  Used for
      AS-external-LSAs.  A router that originates AS scoped LSAs is
      considered an AS Boundary Router (ASBR) and will set its E-bit in
      Router-LSAs for regular areas.

I'm concerned about the impact of this statement for future application of 
text in 3.4.4

   It is expected that new LSAs will be defined that will not be
   processed during the Shortest Path First (SPF) calculation as
   described in Section 3.8.  For example, OSPFv3 LSAs corresponding to
   information advertised in OSPFv2 using opaque LSAs [OPAQUE].

But in 3.4.4 it also says

   To facilitate inter-area reachability validation, any OSPFv3 router
   originating AS scoped LSAs is considered an AS Boundary Router
   (ASBR).

You are saying that the only router that cause AS scoped flooding is an 
ASBR. This limit seems to be unnecessary and overly restrictive.

Further, this seems to be a change from RFC2740 where section 2.3 had only
   o   AS scope. LSA is flooded throughout the routing domain. Used
       for AS-external-LSAs.

Can you clarify why a non-ASBR is not allowed to originate an AS-scoped LSA?

Thanks,
Adrian

PS. I think the I-D header should include "Obsoletes RFC2740" 

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---

From: Igor Bryskin <[email-masked]>
Date: Wed, 10 Oct 2007 09:54:44 -0400

Hi Adrian,

I'd just like to put my 2 cents here.

If a non-ASBR advertises AS-scope LSA and then dies, then there would be
no way for routers in other areas to "feel" that, hence they will be
using the stale information for some while.

Note that the way we fixed the problem with AS-scope opaque LSAs in
OSPF2 is by making the advertising routers ASBRs.

Cheers,
Igor

-----Original Message-----
From: Adrian Farrel [mailto:[email-masked]] 
Sent: Wednesday, October 10, 2007 9:31 AM
To: [email-masked]
Subject: [OSPF] Question on flodding scope
indraft-ietf-ospf-ospfv3-update-17.txt

Hi,

In section 2.3...

I'm concerned about the impact of this statement for future application
of 
text in 3.4.4

Further, this seems to be a change from RFC2740 where section 2.3 had
only
   o   AS scope. LSA is flooded throughout the routing domain. Used
       for AS-external-LSAs.

Can you clarify why a non-ASBR is not allowed to originate an AS-scoped
LSA?

Thanks,
Adrian

---

From: Atanu Ghosh <[email-masked]>
Date: Wed, 10 Oct 2007 07:06:13 -0700

Hi,

If a router is an ASBR then border routers will generate a Summary-LSA
into other areas. If a non-ASBR generates an AS scoped LSA the router
will never be reachable from other areas.

     Atanu.

>>>>> "Adrian" == Adrian Farrel <[email-masked]> writes:

    Adrian> Hi, In section 2.3...

    Adrian>   o AS scope.  LSA is flooded throughout the routing domain.
    Adrian> Used for AS-external-LSAs.  A router that originates AS
    Adrian> scoped LSAs is considered an AS Boundary Router (ASBR) and
    Adrian> will set its E-bit in Router-LSAs for regular areas.

    Adrian> I'm concerned about the impact of this statement for future
    Adrian> application of text in 3.4.4

    Adrian>   It is expected that new LSAs will be defined that will not
    Adrian> be processed during the Shortest Path First (SPF)
    Adrian> calculation as described in Section 3.8.  For example,
    Adrian> OSPFv3 LSAs corresponding to information advertised in
    Adrian> OSPFv2 using opaque LSAs [OPAQUE].

    Adrian> But in 3.4.4 it also says

    Adrian>   To facilitate inter-area reachability validation, any
    Adrian> OSPFv3 router originating AS scoped LSAs is considered an AS
    Adrian> Boundary Router (ASBR).

    Adrian> You are saying that the only router that cause AS scoped
    Adrian> flooding is an ASBR. This limit seems to be unnecessary and
    Adrian> overly restrictive.

    Adrian> Further, this seems to be a change from RFC2740 where
    Adrian> section 2.3 had only o AS scope. LSA is flooded throughout
    Adrian> the routing domain. Used for AS-external-LSAs.

    Adrian> Can you clarify why a non-ASBR is not allowed to originate
    Adrian> an AS-scoped LSA?

    Adrian> Thanks, Adrian

    Adrian> PS. I think the I-D header should include "Obsoletes
    Adrian> RFC2740"

    Adrian> _______________________________________________ OSPF mailing
    Adrian> list [email-masked]
    Adrian> https://www1.ietf.org/mailman/listinfo/ospf

---

From: "Adrian Farrel" <[email-masked]>
Date: Wed, 10 Oct 2007 15:19:53 +0100

I understand the problem, but no the solution!

These advertising routers are not ASBRs unless they have links to other 
ASes.

Seems like the problem should be described in terms of ABRs. If an ABR is 
given special function for flooding AS-scoped LSAs into other areas, it 
should also be given special function for withdrawing those LSAs if *it* 
cannot reach the originator and the originator is supposed to be in the area 
from which the flooding takes place.

The alternative is to fix the language! The originator is not an ASBR, it is 
an originator of AS-scoped LSAs.

A
----- Original Message ----- 
From: "Igor Bryskin" <[email-masked]>
To: "Adrian Farrel" <[email-masked]>; <[email-masked]>
Sent: Wednesday, October 10, 2007 2:54 PM
Subject: RE: [OSPF] Question on flodding scope 

Hi Adrian,

Cheers,
Igor

-----Original Message-----
From: Adrian Farrel [mailto:[email-masked]]
Sent: Wednesday, October 10, 2007 9:31 AM
To: [email-masked]
Subject: [OSPF] Question on flodding scope

Hi,

In section 2.3...

Thanks,
Adrian

---

From: Igor Bryskin <[email-masked]>
Date: Wed, 10 Oct 2007 11:03:12 -0400

I agree with the alternative :=). This is because originally only Type 5
LSAs were of AS scope, hence is the term.

I disagree with what you are writing about ABRs. When flooding AS-scope
LSAs ABRs as far as I know are no different from any other nodes. One of
the functions of ABRs though is to identify ASBRs in areas the ABRs are
responsible for, and properly advertise Summary ASBR LSAs (area-scope)
into adjacent areas.

Igor

-----Original Message-----
From: Adrian Farrel [mailto:[email-masked]] 
Sent: Wednesday, October 10, 2007 10:20 AM
To: [email-masked]
Subject: Re: [OSPF] Question on flodding
scopeindraft-ietf-ospf-ospfv3-update-17.txt

Seems like the problem should be described in terms of ABRs. If an ABR
is 
given special function for flooding AS-scoped LSAs into other areas, it 
should also be given special function for withdrawing those LSAs if *it*

cannot reach the originator and the originator is supposed to be in the
area 
from which the flooding takes place.

The alternative is to fix the language! The originator is not an ASBR,
it is 
an originator of AS-scoped LSAs.

A
----- Original Message ----- 
From: "Igor Bryskin" <[email-masked]>
To: "Adrian Farrel" <[email-masked]>; <[email-masked]>
Sent: Wednesday, October 10, 2007 2:54 PM
Subject: RE: [OSPF] Question on flodding scope 

Hi Adrian,

Cheers,
Igor

-----Original Message-----
From: Adrian Farrel [mailto:[email-masked]]
Sent: Wednesday, October 10, 2007 9:31 AM
To: [email-masked]
Subject: [OSPF] Question on flodding scope

Hi,

In section 2.3...

Thanks,
Adrian

---

From: Acee Lindem <[email-masked]>
Date: Wed, 10 Oct 2007 11:18:56 -0400

Hi Adrian,

On Oct 10, 2007, at 9:30 AM, Adrian Farrel wrote:

> for
> I'm concerned about the impact of this statement for future  
> application of text in 3.4.4
>
> You are saying that the only router that cause AS scoped flooding  
> is an ASBR. This limit seems to be unnecessary and overly restrictive.
>

This is necessary to enforce the "condition of reachability" for all  
LSAs. In other words, in order for an LSA to be considered valid, you  
need to verify that the advertising router is reachable. Hence, a  
router advertising an AS scoped LSA must advertise itself as ASBR so  
that Inter-Area-Router-LSAs are advertised into all regular areas.

We are also respinning RFC 2370 (Opaque LSAs) to enforce this. This  
is  draft-ietf-ospf-rfc2370bis-01.txt.

Thanks,
Acee

---

From: Acee Lindem <[email-masked]>
Date: Wed, 10 Oct 2007 11:28:22 -0400

Hi Adrian,

On Oct 10, 2007, at 10:19 AM, Adrian Farrel wrote:

> These advertising routers are not ASBRs unless they have links to  
> other ASes.
>
> Seems like the problem should be described in terms of ABRs. If an  
> ABR is given special function for flooding AS-scoped LSAs into  
> other areas, it should also be given special function for  
> withdrawing those LSAs if *it* cannot reach the originator and the  
> originator is supposed to be in the area from which the flooding  
> takes place.
>
> The alternative is to fix the language! The originator is not an  
> ASBR, it is an originator of AS-scoped LSAs.

I could modify the definition of the Router E bit to include both  
situations. However, I don't want to define a new bit since we only  
have 8 router bits total in the Router-LSA (and only 4 left assuming  
we can reclaim the bit from MOSPF).

Thanks,
Acee

>
> A
> ----- Original Message ----- From: "Igor Bryskin"  
> <[email-masked]>
> Subject: RE: [OSPF] Question on flodding scope indraft-ietf-ospf- 
> ospfv3-update-17.txt
>
>
> Hi Adrian,
>
> application
> is an

---

From: "Nitin Kakkar" <[email-masked]>
Date: Wed, 10 Oct 2007 11:02:00 -0700

Adrian> You are saying that the only router that cause AS scoped
flooding is an ASBR. This limit seems to be unnecessary and overly
restrictive.

Adrian> Can you clarify why a non-ASBR is not allowed to originate an
AS-scoped LSA?

Acee> This is necessary to enforce the "condition of reachability" for
all LSAs. In other words, in order for an LSA to be considered valid,
you need to verify that the advertising router is reachable. Hence, a
router advertising an AS scoped LSA must advertise itself as ASBR so
that Inter-Area-Router-LSAs are advertised into all regular areas. 

IMHO> It is quite possible in many scenario's that  a router originated
AS scope LSA's and then changed from ASBR to Non ASBR, leaving older ASE
LSA's in domain.  

1)     If we use implict definition of ASBR (independent of E bit) it
will result in incorrect  Routes 

2)     This statement also tries to prevent unnecessary origination of
unusable lsa's (If router originate ASE lsa's and does not advertise it
self as ASBR, what would be the use of those LSA's?  these LSA's will
only occupy space in LSDB & result into unnecessary flooding but won't
contribute to routing, this is very similar to  )  

Regards

Nitin

________________________________

From: Acee Lindem [mailto:[email-masked]] 
Sent: Wednesday, October 10, 2007 8:19 AM
To: Adrian Farrel
Cc: [email-masked]
Subject: Re: [OSPF] Question on flodding scope
indraft-ietf-ospf-ospfv3-update-17.txt

Hi Adrian,

Hi,

In section 2.3...

of text in 3.4.4

  (ASBR).

      for AS-external-LSAs.

This is necessary to enforce the "condition of reachability" for all
LSAs. In other words, in order for an LSA to be considered valid, you
need to verify that the advertising router is reachable. Hence, a router
advertising an AS scoped LSA must advertise itself as ASBR so that
Inter-Area-Router-LSAs are advertised into all regular areas. 

We are also respinning RFC 2370 (Opaque LSAs) to enforce this. This is
draft-ietf-ospf-rfc2370bis-01.txt.

Thanks,

Acee

Thanks,

Adrian

 

OSPF mailing list

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---

From: Acee Lindem <[email-masked]>
Date: Wed, 10 Oct 2007 14:19:43 -0400

Hi Nitin,

On Oct 10, 2007, at 2:02 PM, Nitin Kakkar wrote:

> an AS-scoped LSA?
> Acee> This is necessary to enforce the "condition of reachability"  
> for all LSAs. In other words, in order for an LSA to be considered  
> valid, you need to verify that the advertising router is reachable.  
> Hence, a router advertising an AS scoped LSA must advertise itself  
> as ASBR so that Inter-Area-Router-LSAs are advertised into all  
> regular areas.
>
>
>
> IMHO> It is quite possible in many scenario’s that  a router  
> originated AS scope LSA’s and then changed from ASBR to Non ASBR,  
> leaving older ASE LSA’s in domain.
>
> 1)     If we use implict definition of ASBR (independent of E bit)  
> it will result in incorrect  Routes
>
> 2)     This statement also tries to prevent unnecessary origination  
> of unusable lsa’s (If router originate ASE lsa’s and does not  
> advertise it self as ASBR, what would be the use of those LSA’s?   
> these LSA’s will only occupy space in LSDB & result into  
> unnecessary flooding but won’t contribute to routing, this is very  
> similar to  )
So, I'll take this as agreement.

Thanks,
Acee
> Subject: Re: [OSPF] Question on flodding scope indraft-ietf-ospf- 
> ospfv3-update-17.txt
>
>
>
> Hi Adrian,
>
>
>
> This is necessary to enforce the "condition of reachability" for  
> all LSAs. In other words, in order for an LSA to be considered  
> valid, you need to verify that the advertising router is reachable.  
> Hence, a router advertising an AS scoped LSA must advertise itself  
> as ASBR so that Inter-Area-Router-LSAs are advertised into all  
> regular areas.
>
>
>

---

From: "Nitin Kakkar" <[email-masked]>
Date: Wed, 10 Oct 2007 11:29:26 -0700

From: Acee Lindem [mailto:[email-masked]] 
Sent: Wednesday, October 10, 2007 11:20 AM
To: Nitin Kakkar
Cc: Adrian Farrel; [email-masked]
Subject: Re: [OSPF] Question on flodding scope
indraft-ietf-ospf-ospfv3-update-17.txt

Hi Nitin,

1)     This statement also tries to prevent unnecessary origination of

Nitin> Yes Sir, Agreement to your Statement.

           My statement was in explanation to Adrian's mention  that
ASBR definition is overly restrictive. I tried to point out that
restrictive ASBR definition was necessary for maintaining sanity in ospf
& tried to explain what happen when non asbr's originate ASE lsa's.

Regards

Nitin

Thanks,

Acee

Regards

Nitin

Cc: [email-masked] <mailto:[email-masked]> 

Hi Adrian,

Hi,

In section 2.3...

  (ASBR).

      for AS-external-LSAs.

Thanks,

Acee

Thanks,

Adrian

 

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