Hi Igor,
On Nov 19, 2005, at 11:16 AM, Igor Bryskin wrote:
Hi everybody,
I'd like to note that although the AS scope flooding is allowed for
opaque
LSAs, in my experience it does not work.
So your experience is different than the one of many people ... Opaque
LSA have been
used for quite a few years without any problem. See RFC2370 (July 1998)
Imagine that some routing
controller advertises an AS scope LSA and goes out of service quickly
after
that. Controllers outside of the area that the dead controller
belongs to
have no way of detecting its death and, therefore, will keep using the
advertising for another 90 min before the LSA times out.
I guess that you mean 60 min (Maxage=60mn, Architectural Constant) -
See RFC2328, but this is not the point, see below.
Note that the
controllers located within the same area do not have such a problem
because
they can always verify the validity of the advertising by trying to
locate a
sequence of active adjacencies interconnecting each of them with the
advertising controller. If they find at least one such a sequence, the
advertising is valid (otherwise, it would be withdrawn); on the other
hand,
if no such sequences exist, than advertising is likely to be stale
and hence
could not be trusted. The conclusion is that opaque LSAs should never be
flooded within AS, rather, within a single area, and, if there is a
need for
the information to be propagated beyond the area boundaries, ABRs
must relay
the advertising into other areas (by originating new area-scope
LSAs). Note
also that as far as I remember OSPF itself never uses AS scope
advertisings
for its own needs. For example, an ASBR does not distribute external
routes
learned by BGP from other ASs using AS scope LSAs, rather, the routes
are
advertised within a single area and ABRs relay the advertisings into
other
areas.
This is not correct. External routes are redistributed with LSA Type 5
which are
flooded across the entire domain except in stub-area (not generated by
the ABR as type 3 as you mention).
Anyway, back to the point, one cannot say of course that "Opaque LSA
Type 11 does not work". There are suitable to some application, this is
all. You can perfectly reply on an opaque LSA Type 11 to learn the
capability of a router which does not reside in the local area and rely
on another mechanism to detect its liveness. There are several such
examples.
Hope this helps.
JP.
The bottom line is that the TLVs described in the draft should be of the
area scope (just like TE LSAs), and hence it is not all that important
whether we use new high level TLVs or sub-TLVs of the TE router cap TLV.
Igor
----- Original Message -----
From: "dimitri papadimitriou" <dpapadimitriou@psg.com>
To: "Adrian Farrel" <adrian@olddog.co.uk>
Cc: "LE ROUX Jean-Louis RD-CORE-LAN"
<jeanlouis.leroux@francetelecom.com>;
"JP Vasseur" <jvasseur@cisco.com>; "Dimitri Papadimitriou"
<dimitri.papadimitriou@alcatel.be>; <ccamp@ops.ietf.org>
Sent: Friday, November 18, 2005 10:57 AM
Subject: Re: IGP Extensions - CCAMP Milestones
adrian
i think JL's reply did partially translate the initial concern
in brief, there are three well identified TE applications that could
make use of the TE node cap TLVs on both intra and inter-area basis:
- LSP Stitching edge node capability
- Edge nodes connecting/being P2MP TE egresses
- TE auto-mesh
hence, the question on why keeping separated TLVs as part of the router
capability and not consider these as sub-TLVs of the TE router cap TLV
this would
1) provide a logical grouping of TE sub-TLVs as part of the same TLV
and
2) leave the flexibility of flooding scope on a per application need -
note: that the path computation specific sub-TLVs could still be
restricted with their current area-scope
hope this clarifies the issue,
thanks,
- dimitri.
Adrian Farrel wrote:
If I understand the question it is...
In draft-ietf-ospf-cap-07.txt introduces the OSPF router
information LSA
and states that this LSA may have type 9, 10 or 11 scope.
In draft-vasseur-ccamp-te-node-cap-01.txt a new TLV (TE Node
Capability
Descriptor) is added to the OSPF router information LSA. This TLV
(when
generated) MUST be advertised with type 10 scope. JL has given the
reason
why this is limited to type 10. This reason is, of course, open for
discussion as he says.
In draft-vasseur-ccamp-automesh-02.txt a new TLV (TE-MESH-GROUP) is
added
to the OSPF router information LSA. It states that the LSA may be
advertised with type 10 or type 11 scope. JP has given a reason why
you
might want type 11 in addition to type 10. This reason is, of course,
open
for discussion.
An interesting feature is that a router advertising an AS-wide mesh
group
*and* a TE router capability may require that two OSPF router
information
LSAs are advertised by the router.
The language in draft-ietf-ospf-cap-07.txt leans towards a router
sending
*an* OSPF router information LSA. But nowhere does it say that the
router
cannot send more than one and in section 2.5 we find...
The originating router MAY advertise
multiple RI LSAs as long as the flooding scopes differ.
Hope this answers the point.
Adrian
----- Original Message -----
From: "LE ROUX Jean-Louis RD-CORE-LAN"
<jeanlouis.leroux@francetelecom.com>
To: "JP Vasseur" <jvasseur@cisco.com>; "Dimitri Papadimitriou"
<dpapadimitriou@psg.com>; "Dimitri Papadimitriou"
<dimitri.papadimitriou@alcatel.be>
Cc: <adrian@olddog.co.uk>; <ccamp@ops.ietf.org>
Sent: Thursday, November 17, 2005 6:47 PM
Subject: RE: IGP Extensions - CCAMP Milestones
Hi Dimitri,
Thanks for the comment.
As just explained by JP, the TE Node Cap TLV carries topology related
parameters used as constraints in path computation. The leaking of
such
info across areas sounds useless as LSR TE visibility is limited to
one
area anyway...
But this is, of course, open to discussions. By the way, do you
have any
application in mind where such leaking would be useful?
Regards,
JL
-----Message d'origine-----
De : JP Vasseur [mailto:jvasseur@cisco.com]
Envoyé : jeudi 17 novembre 2005 16:58
À : Dimitri Papadimitriou; Dimitri Papadimitriou
Cc : zzx-adrian@olddog.co.uk; ccamp@ops.ietf.org; LE ROUX
Jean-Louis RD-CORE-LAN
Objet : Re: IGP Extensions - CCAMP Milestones
Hi dimitri,
On Nov 16, 2005, at 6:30 PM, dimitri papadimitriou wrote:
adrian,
could you explain the reasoning for having a TE specific TLV in the
auto-mesh document with area and AS-wide flooding scope
while the TE
router cap TLV is restricted to an area flooding scope ?
shouldn't be one way or the other i.e. either restrict all TE info
area-local or allow for TE router cap TLV with AS-wide
flooding scope
?
note: there is nothing in the TE router cap TLV that would impact
scaling more than the TE auto-mesh TLV does
I guess that the reason for allowing both intra and inter-area
flooding scopes for automesh is obvious (we need to have TE LSP mesh
within areas and spanning multiple areas).
So your question is probably why don't we allow the TE router
cap TLV
to be flooded across the domain ? As far as I can remember JL
already
answered this question ... JL, could you forward your email again ?
In the meantime, I can answer it: the reason is that such TE node
capabilities are used for TE LSP computation which cannot take into
account nodes that do not reside in the node's area.
Thanks.
JP.
thanks,
- dimitri.
Adrian Farrel wrote:
Hi,
We have two immediate milestones to address:
Oct 05 First version WG I-D for Advertising TE Node Capabilities
in ISIS
and OSPF
Oct 05 First version WG I-D for Automatic discovery of
MPLS-TE mesh
membership
There are two personal submissions which address these topics:
draft-vasseur-ccamp-te-node-cap-01.txt
draft-vasseur-ccamp-automesh-02.txt
I propose that we move these into the WG and then kick the tires
thoroughly.
Opinions please.
Thanks,
Adrian
.
.
.