Subject: [bmwg] OSPF convergence terminology

From: "Howard C. Berkowitz" <[email-masked]>
Date: Wed, 19 Dec 2001 09:39:38 -0500

I'm delighted that someone is taking on this work. Quite frankly, we 
considered BGP convergence (without extensive policy) to be a simpler 
problem in many respects.  Most comments here deal with lessons 
learned as our documents evolved.

Comments inline, with snippage for space.  Apologies for the mess 
made by Mac and Eudora reformatting...will do it differently next 
time.

--------------------
>Network Working Group                                     Vishwas 
>Manral Internet Draft 
>Netplane Networks 
>Russ White Expiration Date: June 2002 
>Cisco Systems File Name: draft-manral-ospfconv-term-00.txt 
>December 2001                OSPF Benchmarking Terminology and 
>Concepts                    draft-manral-ospfconv-term-00.txt

>2. Abstract    This draft explains the terminology and concepts used 
>in [2] and    future OSPF benchmarking drafts. INTERNET DRAFT 
>OSPF Benchmarking Terminology         December 2001

>3. Conventions used in this document    The key words "MUST", "MUST 
>NOT", "REQUIRED", "SHALL", "SHALL NOT",    "SHOULD", "SHOULD NOT", 
>"RECOMMENDED", "MAY", and "OPTIONAL" in this    document are to be 
>interpreted as described in [1].

>4. Motivation    This draft is a companion to [2], which describes 
>basic Open Shortest    Path First (OSPF [3]) testing methods. This 
>draft explains    terminology and concepts used in OSPF Testing 
>Framework Drafts, such    as [2].

>5. Definitions

Internal and external measurements, also called, respectively, white 
box and black box, are a basic issue in convergence testing. In the 
BGP convergence work, we elected to emphasize external measurements 
for several reasons:

     -- collecting the data inside the router MAY increase loading on it
        and give the effect of reduced performance
     -- a given implementation may not have the interfaces needed for
        internal testing.
     -- time synchronization among the sources, sinks, and DUT may be
        more difficult, especially if NTP proves inadequate.

There are other factors, but the general topic of internal versus 
external measurement is probably well worth discussing as a WG-wide 
subject.  I don't think it's desirable to have some protocols 
measured internally and others measured externally.

>    o    Internal Measurements

>-    Definition               Internal measurements are measurements 
>taken on the Device               Under Test (DUT) itself.

>-    Discussion               These measurement rely on output and 
>event recording,               along with the clocking and 
>timestamping available on the               DUT itself. Internal 
>measurements are preferred for all               tests that can be 
>completely contained on the DUT (which               is very rare).

>  o    External Measurements          -    Definition 
>External measurements infer the performance of the DUT 
>through observation of its communications with other dev- 
>ices.          -    Discussion               One example of an 
>external measurement is when a down-               stream device 
>receives complete routing information from               the DUT, it 
>can be inferred that the DUT has transmitted               all the 
>routing information available.               For the purposes of 
>this paper, external technique are               more readily 
>applicable. However, external measurements               have their 
>own problems because they include the time to 
>advertise the new route downstream and transmission times 
>for the advertisement within the device under test.

In the BGP convergence work, we are attempting to define measurement 
points at which these additional times can be factored out. It is not 
a trivial task, especially when you are dealing with >1 load source.

>       o    Multi-device Measurements          -    Definition 
>Multi-device measurements require the measurement of 
>events occuring on multiple devices within the testbed.          - 
>Discussion               For instance, the timestamp on a device 
>generating an               event could be used as the marker for 
>the beginning of a               test, while the timestamp on the 
>DUT or some other device               might be used to determine 
>when the DUT has finished pro-               cessing the event. 
>These sorts of measurements are the most problematic, and 
>are to be avoided where possible, since the timestamps of 
>the devices in the test bed must be synchronized within 
>milliseconds for the test results to be meaningful. Given 
>the state of network time protocol implementation, expect- 
>ing the timestamps on several devices to be within mil- 
>liseconds of each other is highly optimistic.

>o    Point-to-Point links          -    Definition               A 
>network that joins a single pair of routers is called a 
>point-to-point link. For OSPF [3], point-to-point links 
>are those on which a designated router are not elected.          - 
>Discussion               A point-to-point link will take lesser time 
>to converge               than a braodcast link of the same speed 
>because it does               not have the overhead of DR election. 
>Point-to-point links               can be either numbered or 
>unnumbered. However in the con-               text of [2], the two 
>can be regarded the same.

>o    Broadcast Link          -    Definition               Networks 
>supporting many (more than two) attached routers, 
>together with the capability to address a single physical 
>message to all of the attached routers (broadcast). In the 
>context of [2] and [3], broadcast links are taken as those 
>on which a designated router is elected.          -    Discussion 
>The adjacency formation time on a broadcast link can be 
>more than that on a point-to-point link of the same speed, 
>because DR election has to take place. All routers on a 
>broadcast network form adjacency with the DR and BDR. 
>Async flooding also takes place thru the DR. In context of 
>convergence, it may take more time for an LSU to be 
>flooded from one DR-other router to another DR-other 
>router, because the LSA has to be first processsed at the 
>DR.

For completeness, should you not deal with NBMA and demand links, and 
possibly any special cases associated with virtual links and stub 
routes?

>       o    Shortest Path First Time          -    Definition 
>The time taken by a router to complete the SPF process.          - 
>Discussion               This does not include the time taken by the 
>router to give               routes to the forwarding engine.

>o    Measurement Units               The LSA time is generally 
>measured in milliseconds.

We should not preclude the experimental work going on that puts these 
times into the microsecond range.

>       o    Hello Interval          -    Definition               The 
>length of time, in seconds, between the Hello Packets 
>that the router sends on the interface.          -    Discussion 
>The hello interval should be the same for all routers on 
>the network               Decreasing the hello interval can allow 
>the router dead               interval (below) to be reduced, thus 
>reducing convergence               times in those situations where 
>the router dead interval               timing out causes an OSPF 
>process to notice an adjacency               failure. Very small 
>router dead intervals accompanied by               very small hello 
>intervals can produce more problems than               they resolve, 
>as described in [4] & [5].

It's probably worth discussing the reality that there can be 
different hello/dead intervals depending on link type (e.g., NBMA).

>       o    Router Dead interval          -    Definition 
>After ceasing to hear a router's Hello Packets, the number 
>of seconds before its neighbors declare the router down.          - 
>Discussion               This is advertised in the router's Hello 
>Packets in the               RouterDeadInterval field. The router 
>dead interval should               be some multiple of the 
>HelloInterval (say 4 times the               hello interval), and 
>must be the same for all routers               attached to a common 
>network.

>6. Concepts

>6.1.  A network is termed to be converged when all of the devices 
>within    the network have a loop free path to each possible 
>destination. Since    we are not testing network convergence, but 
>performance for a partic-    ular device within a network, however, 
>this definition needs to be    narrowed somewhat to fit within a 
>single device view.    In this case, convergence will mean the point 
>in time when the DUT    has performed all actions needed to react to 
>the change in topology    represented by the test condition; for 
>instance, an OSPF device must    flood any new information it has 
>received, rebuild its shortest path    first (SPF) tree, and install 
>any new paths or destinations in the    local routing information 
>base (RIB, or routing table).

>6.2. Measuring Convergence    Obviously, there are several elements 
>to convergence, even under the    definition given above for a 
>single device. We will try to provide    tests to measure each of 
>these:       o    The time it takes for the DUT to pass the 
>information about a            network event on to its neighbors.

>o    The time it takes for the DUT to process information about a 
>network event and calculate a new Shortest Path Tree (SPT).

>o    The time it takes for the DUT to make changes in its local 
>rib reflecting the new shortest path tree.

Is there an assumption here that the entire new SPT tree is presented 
to the RIB installation process as a single unit, or could the 
presentation be incremental?

>6.3. Types of Network Events

>o    Link or Neighbor Device Up            The time needed for an 
>OSPF implementation to recoginize a            new link coming up on 
>the device, build any necessarily adja-            cencies, 
>synchronize its database, and perform all other            needed 
>actions to converge.

>o    Initialization            The time needed for an OSPF 
>implemention to be initialized,            recognize any links 
>across which OSPF must run, build any            needed adjacencies, 
>synchronize its database, and perform            other actions 
>needed to converge.

>o    Adjacency Down            The time needed for an OSPF 
>implementation to recognize a            link down/adjacency loss 
>based on hello timers alone, propo-            gate any information 
>as necessary to its remaining adjacen-            cies, and perform 
>other actions needed to converge.

>o    Link Down            The time needed for an OSPF implementation 
>to recognize a            link down based on layer 2 provided 
>information, propogate            any information information as 
>needed to its remaining adja-            cencies, and perform other 
>actions needed to converge. 6.4. LSA and Destination mix

This material is probably more appropriate for the methodology 
document. We also started with it in terminology, but found it worked 
better in methodology.

>    In many OSPF benchmark tests, a generator injecting a number of 
>LSAs    is called for. There are several areas in which injected 
>LSAs can be    varied in testing:

>o    The number of destinations represented by the injected LSAs 
>Each destination represents a single reachable IP network; 
>these will be leaf nodes on the shortest path tree. The pri- 
>mary impact to performance should be the time required to 
>insert destinations in the local routing table and handling 
>the memory required to store the data.

>o    The types of LSAs injected            There are several types 
>of LSAs which would be acceptable            under different 
>situations; within an area, for instance,            type 1, 2, 3, 
>4, and 5 are likely to be received by a router.            Within a 
>not-so-stubby area, however, type 7 LSAs would            replace 
>the type 5 LSAs received. These sorts of characteri- 
>zations are important to note in any test results.

>o    The Number of LSAs injected            Within any injected set 
>of information, the number of each            type of LSA injected 
>is also important. This will impact the            shortest path 
>algorithms ability to handle large numbers of            nodes, 
>large shortest path first trees, etc.       o    The Order of LSA 
>Injection            The order in which LSAs are injected should not 
>favor any            given data structure used for storing the LSA 
>database on the            device under test. The ordering can be 
>changed in various            tests to provide insight on the 
>efficency of storage within            the DUT. Any such changes in 
>ordering should be noted in test            results. 6.5. Tree Shape 
>and the SPF Algorithm

Again, we found this to be a methodology issue.

>    The shortest path first algorithm is a simple algorithm which 
>handles    complexity by breaking the problem of finding the 
>shortest paths    through a network into smaller parts and recursing 
>(calling itself)    to compute the best path within each smaller 
>part. Because of this,    moving along a single level of the tree, 
>along the tree's width, is    fundamentally different than moving 
>along the depth of the tree.                root        root 
>/    \        |              1      2       1             / \    / \ 
>|            3   4  5   6     2                             | 
>3                             |                             4 
>|                             5                             | 
>6    For instance, the shortest path first algorithm would go 
>through two    recursions when finding the shortest paths on the 
>left topology, with    an average of two nodes processed per level. 
>The topology on the    right would produce five recursions, with one 
>node processed per    recursion.  While this may not produce 
>dramatically different test    results, there may be some apparent 
>difference between the two.    In general, those benchmarking link 
>state protocols which use the    shortest path first algorithm to 
>compute the best paths through the    network need to be aware that 
>the construction of the tree may impact    the performance of the 
>algorithm. Best practice would be to try and    make any emulated 
>network look as much like a real network as possi-    ble, 
>especially in the area of the tree depth, the meshiness of the 
>network, the number of stub links verses transit links, and the 
>number of connections and nodes to process at each recursion level. 
>7. Route Generation

Methodology again.

>    As the size of networks grows, it becomes more and more difficult 
>to    actually create a large scale network on which to test the 
>properties    of routing protocols and their implementations. In 
>general, network    emulators are used to provide emulated 
>topologues which can be adver-    tised to a device with varying 
>conditions. Route generators either    tend to be a specialized 
>device, a piece of software which runs on a    router, or a process 
>that runs on another operating system, such as    Linux or another 
>variant of Unix.    Some of the characteristics of this device 
>should be:

>o    The ability to connect to the several devices using both point- 
>to-point and broadcast high speed media. Point-to-point links can 
>be emulated with high speed Ethernet as long as there is no hub or 
>other device in between the DUT and the route generator, and the 
>link is configured as a point-to-point link within OSPF.

>o    The ability to create a set of LSAs which appear to be a 
>logical,       realistic topology. For instance, the generator 
>should be able to       mix the number of point-to-point and 
>broadcast links within the       emulated topology, and should be 
>able to inject varying numbers of       externally reachable 
>destinations.

>o    The ability to withdraw and add routing information into and 
>from       the emulated topology to emulate links flapping.

>o    The ability to randomly order the LSAs representing the 
>emulated       topology as they are advertised.

>o    The ability to log or otherwise measure the time between 
>packets       transmitted and received.

>o    The ability to change the rate at which OSPF LSAs are transmitted.

>8. Acknowedgements    The authors would like to thank Aman Shaikh 
>([email-masked]) for his comments and help on this draft.

>9. References [1]  Bradner, S., "Key words for use in RFCs to 
>Indicate Requirement      Levels", RFC2119, March 1997. [2]  Manral, 
>V., "Benchmarking Methodology for Basic OSPF Convergence", 
>draft-manral-ospconv-intraarea-00, November 2001 [3]  Moy, J., "OSPF 
>Version 2", RFC 2328, April 1998. [4] 
>draft-ash-ospf-isis-congestion-control-01.txt [5] 
>draft-ietf-ospf-scalability-00.txt 10. Authors' Addresses 
>Vishwas Manral,       Netplane Networks,       189 Prashasan Nagar, 
>Road number 72,       Jubilee Hills,       Hyderabad. 
>[email-masked]       Russ White       Cisco Systems, Inc. 
>7025 Kit Creek Rd.       Research Triangle Park, NC 27709 
>[email-masked]

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bmwg mailing list
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http://www1.ietf.org/mailman/listinfo/bmwg

---

From: "Manral, Vishwas" <[email-masked]>
Date: Wed, 19 Dec 2001 12:32:02 -0500

Howard,

Thanks a lot for all the helpful comments. My comments inline prefixed with
a VM>

Thanks,
Vishwas

VM> Agreed. Most of the tests in the methodology draft for OSPF use external
measurements, with one exception. Although for measuring SPF time we have a
test using external measurements, we generally prefer internal measurements.
As SPF times can be in units of microseconds, external measurements may not
be appropriate for the purpose(i think it is hard to get that level of
accuracy). We have readily available outputs in the few routers I have come
across, which give the outputs(without distorting the readings, as they are
not "Log outputs" but show commands)

VM> Well, although we could have done tests for all kinds of links(including
NBMA and P2MP), in all types of areas(NSSA, stub, normal), we have just done
it on two kinds of links.

The only difference in the convergence times on different kinds of links
would be because of DR election(adjacencies start building once we decide
who the DR is). That is why we have taken one case of where no DR election
takes place(broadcast, it could have been NBMA too) and one case where we
dont(P2P, it could have been P2MP too) Or do you think we should still have
tests using all kinds of interfaces?

VM> For internal measurement it is possible, getting reading correct to that
accuracy when using external measurement in my view would not be possible. I
have read thru Chengiz draft on IGP convergence, I think that too talks
about millisecond convergence.

VM> OK.

VM> We have two tests for measuring SPF time. The LSA's are sent in one at a
time, and so are installed in order, measurements however are not done at
this moment. After we have all the necessary LSA's in the database, for both
internal as well as external measurements we create such a condition(change
in a particular router LSA, by change of cost of the link), where the entire
SPF needs to be calculated all over again. Measurements are taken at this
point of time. We have not taken incremental SPF into account.

May be sections 8.3 and 8.4 in the methodology draft will explain it better.

VM> The reason why we have Network events, destination mix, tree shape etc
in the terminology draft was because we thought they were general to all
OSPF convergence methodology drafts(although we have just one for Intra-Area
rite now). We generally assumed we would have one terminology draft , with
may be more than one methodology drafts(Inter-area, inter-domain routes or
even dataplane tests in case of OSPF) I think that would be the case with
BGP too, wouldn't it? 

Any reason why you found the discussion more appropriate in the methodology
draft?

---

From: "Manral, Vishwas" <[email-masked]>
Date: Wed, 19 Dec 2001 12:32:02 -0500

Howard,

Thanks,
Vishwas

VM> OK.

---

From: "Manral, Vishwas" <[email-masked]>
Date: Wed, 19 Dec 2001 12:39:32 -0500

Randy,

>i am used to 'convergence' being a matter of MANY routers coming to the
same
>view of the routing universe.  as the bmwg's scope is a single device, i
>don't think we should be using the term 'convergence' at all.
May be you are right, but what could be a more appropriate term for it?

>and be specific.  do you mean the rib 'settling' or the fib?
OSPF 'convergence' draft talks about rib 'settling' and not the fib, guess
it is the same with BGP convergence.

>randy
Thanks,
Vishwas

---

From: "Howard C. Berkowitz" <[email-masked]>
Date: Wed, 19 Dec 2001 13:03:25 -0500

>test using external measurements, we generally prefer internal measurements.

Thinking a little further, isn't the SPF time more of an 
implementation specific issue anyway?  The RIB installation time 
would seem more generally applicable.  A given implementation might 
have a superfast SPF but a very slow RIB installer, so the 
"convergence time" is a factor of the two.

What is your reasoning for separating out the SPF time? Also, isn't 
the SPF time highly reflective of the number and types of links, 
where the total convergence time (sorry, Randy. It's a placeholder) 
is more operationally useful?

>it on two kinds of links.

True.  But at least NBMA is a curse of the real world. I've probably 
seen more people have problem with NBMA configuration than any other 
operational part of OSPF. Last time I looked, there were around 5 
different ways to configure NBMA on a Cisco router.

>who the DR is).

>That is why we have taken one case of where no DR election

You made a very reasonable choice by differentiating between DR and 
non-DR situations. Maybe I'm reading too much operational 
cluelessness into it, but I would like to see some of the NBMA 
aspects as a reality check for the testing. Consider the following 
topology:  R1 and R2 are hub routers with connections to all the 
spoke routers. The intention, of course, is to have no single point 
of failure, so both R1 and R2 should be eligible to become DR.  If 
there is no virtual circuit between R1 and R2, however, the NBMA can 
get partitioned, have arguments over who is DR, and generally be 
confused.

>about millisecond convergence.

That's what I was thinking of. Remember that both SPF and hello times 
are involved here, potentially with very fast hellos. Alternatively, 
you might want to consider the alternative to hellos of depending on 
layer 1/2 information to detect link (but not dead router) failure.

>May be sections 8.3 and 8.4 in the methodology draft will explain it better.

OK.  I haven't read your latest methodology draft in detail.

>even dataplane tests in case of OSPF) I think that would be the case with

Yes, that should work.

>Any reason why you found the discussion more appropriate in the methodology

We started out with things such as route mixes in terminology, but 
quickly found they were intimately associated both with the load 
generator requirements and the test report, neither of which "felt 
right" in terminology.

---

From: "Howard C. Berkowitz" <[email-masked]>
Date: Wed, 19 Dec 2001 13:03:25 -0500

Yes, that should work.

---

From: "Karen Webb" <[email-masked]>
Date: Wed, 19 Dec 2001 13:21:48 -0500

Vishwas,

I am new to this group and have not had time to fully look at all of the
drafts so I apologize in advance if my comments do not fit with the
intent of the draft.  Here however, for what they are worth, are my two
cents...

While the definition of the term convergence tends to mean all routers
having the same view of the network, we actually have used it more
liberally in our labs.  When testing before a modification to the
network we test for convergence of a single device, convergence of a
single AS, and end-to-end convergence of our enterprise test bed.  I
believe that convergence is still the most appropriate term but that it
should prefaced with a definition of "what" has been converged.  The
tests for device, AS, and enterprise are actually very different and
therefore the test to their convergence is different.

Karen

________________________________________
Karen M. Webb
Principal Engineer-Bank of America 
Optical Lab

The Signature Group
401 N. Tryon Street, #1037
Charlotte, NC 28202

> -----Original Message-----
> From: Manral, Vishwas [mailto:[email-masked]]
> Sent: Wednesday, December 19, 2001 12:40 PM
> To: 'Randy Bush'; Howard C. Berkowitz
> Cc: [email-masked]
> Subject: RE: [bmwg] OSPF convergence terminology
> 
> Randy,
>

---

From: Scott Bradner <[email-masked]>
Date: Wed, 19 Dec 2001 19:36:06 -0500 (EST)

> systems of boxen is more ippm's domain

well, ippm was envisioned as looking at systems not systems of boxes
i.e. it was not envisioned as looking at the things that hold the systems
together - just how the system works as a unit

i.e. bmwg nor ippm was envisioned as looking at the how something like
routing works or the effects of particular vendor's implementations
but to me bmwg is closer but maybe that is because I worked with
pairs of boxes under test to get some of the measurements

Scott

---

From: Scott Bradner <[email-masked]>
Date: Wed, 19 Dec 2001 19:36:06 -0500 (EST)

Scott

---

From: "Manral, Vishwas" <[email-masked]>
Date: Wed, 19 Dec 2001 23:42:20 -0500

>greenberg's recent paper at isma showed that the biggest chunk of ospf
>settling time was updating the fib from the rib, an unexpected result.
Sorry for the late response. I work in a different time Zone(+5:30 GMT)

I have probably read the paper that you are refering to(we even had our
draft reviewed by both the authors of the paper before we got out the
version !!!), I feel that sending routes from rib to fib is not protocol
specific(so it would be more a matter of how that's implemented for all
protocols and not specific to OSPF) though I agree it would effect when OSPF
routes actually get used.

-Vishwas

---

From: "Manral, Vishwas" <[email-masked]>
Date: Thu, 20 Dec 2001 08:29:10 -0500

Karen,

I sort of agree with you, 'settling' doesn't sound very bmwgish(not to my
ears), may be characterising the kind of convergence would help clarify(as
you have mentioned).

Thanks for the comments. We hope to get further comments from you/the group
on the drafts.

-Vishwas

-----Original Message-----
From: Karen Webb [mailto:[email-masked]]
Sent: Wednesday, December 19, 2001 11:52 PM
To: Manral, Vishwas; Randy Bush; Howard C. Berkowitz
Cc: [email-masked]
Subject: RE: [bmwg] OSPF convergence terminology

Vishwas,

Karen

The Signature Group

---

From: "Manral, Vishwas" <[email-masked]>
Date: Thu, 20 Dec 2001 08:29:10 -0500

Karen,

-Vishwas

-----Original Message-----
From: Karen Webb [mailto:[email-masked]]
Sent: Wednesday, December 19, 2001 11:52 PM
To: Manral, Vishwas; Randy Bush; Howard C. Berkowitz
Cc: [email-masked]
Subject: RE: [bmwg] OSPF convergence terminology

Vishwas,

Karen

The Signature Group

---

From: "Howard C. Berkowitz" <[email-masked]>
Date: Thu, 20 Dec 2001 09:59:11 -0500

>ears), may be characterising the kind of convergence would help clarify(as

Yes, it is behavior I associate with my cat. If ever we try to 
benchmark the performance of tail circuits, he will be a worthy 
contributor.

Simply food for thought here, but there's something in current 
military theory called the Boyd cycle or OODA loop, that perhaps has 
corollaries here

      Observe (collect raw data, as in routing updates)
      Orient  (interpret, as in local policy)
      Decide  (select for main RIB/FIB)
      Act     (advertise new routes and forward)

The military recognizes there are separate but independent OODA loops 
at all levels, from that of an individual fighter pilot to that of an 
air campaign. That sort of hierarchy (with local autonomy) is 
somewhere along the lines we are discussing.

---

From: "Howard C. Berkowitz" <[email-masked]>
Date: Thu, 20 Dec 2001 09:59:11 -0500

---

From: "Manral, Vishwas" <[email-masked]>
Date: Thu, 20 Dec 2001 13:46:34 -0500

Howard,

Comments inline prefixed with a VM>

Thanks again for all the comments,
Vishwas

VM> I may not have I understood ur question properly, however I will try to
answer my interpretation of the question. ;-)

Firstly, we have measured times taken by OSPF specific tasks. The time we
call SPF time, the time to calculate the SPF for OSPF(from start to end).
How the routes are further get to FIB is very implementation specific, and I
feel is not in the scope of OSPF.

To explain the exact why we seperated out SPF time, let me try and explain
tests in the methodology draft. Well we have tried to break up convergence
to(simplified it for one LSA)

convergence time for a lsa(got from an adjacent router) = time to get the
LSA + time to process the LSA + time  diff for scheduling the LSA + SPF time
+ time to give the routes to FIB.

We have tried to measure all individual pieces that are OSPF specific. SPF
time happens to be one of them. (I know it is late here nearly 12:00AM, so I
may not be making all sense, but we have thought the things out)

VM> Ok.

VM> Well ok. I will rethink this up and see how and where it fits in the
draft.

VM> We have a test case for that in the methodology draft, where the
detection of neighbor down is because of indication from a lower layer and
not router dead interval expiry(just the case you have indicated). You might
want to read the scalability draft in OSPF-wg, it is a work on OSPF in a
similar front, with a different conclusion though.

VM> This sounds reasonable, but do you intend to replicate all the stuff all
over again in the iBGP draft if and when that is released.

---

From: "Manral, Vishwas" <[email-masked]>
Date: Thu, 20 Dec 2001 13:46:34 -0500

Howard,

VM> Ok.

---

From: "Howard C. Berkowitz" <[email-masked]>
Date: Thu, 20 Dec 2001 16:07:55 -0500

>answer my interpretation of the question. ;-)

It sounds like what you are describing a two-step process: SPF to 
FIB. I see it as a three-step process: SPF to RIB to FIB.  Think of 
the basic route selection process in RFC 1812 (e.g., most specific 
prefix first), which is certainly post-SPF.

Depending on the implementation, the RIB and FIB _MAY_ be the same 
data structure, but certainly don't have to be. It's quite common to 
have a single RIB but distributed FIBs.

>over again in the iBGP draft if and when that is released.

Probably, although we haven't gotten that far. It's possible there 
may be slight differences, and it's also possible we might split 
route mix into an entirely separate document.

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From: "Howard C. Berkowitz" <[email-masked]>
Date: Thu, 20 Dec 2001 16:07:55 -0500