Subject: Re: Few questions related to LDP

From: [email-masked]
Date: Fri, 8 Jun 2001 11:20:21 +0530

hi abhijit!
     that is eaxctly what I was pointing at and the key thing here is that you
are making R2 "smarter" and the real question would be what level of smartness
should it have in order to be able to induce such a setup. another key thing
would be that this may not scale to all QoS requirements of a network when we
intend to use MPLS for that rather than just hope-by-hope forwarding.

ciao
sumit

Abhijit Gadgil <[email-masked]> on 06/08/2001 06:43:35 AM

To:   Sumit Chauhan/HSS@HSS
cc:   Eric Gray <[email-masked]>, Nagendra Singh Tomar
      <[email-masked]>, [email-masked]

Subject:  Re: Few questions related to LDP

sumit,

If R2 has no entry for p.q.r.o/24, but for p.q.0.0/16 then I think
following shd happen, almost like what Eric has pointed out.

 R1-R2         R2-R3    ( R2 is being a bit smart here)
=======       =======
 LSP1          LSP2
(p.q.r.0/24)  (p.q.0.0/16)

and not

  R1-R2-R3
 ===========
    LSP
(p.q.r.0/24)

If indeed an LSP as in scenario 2 exist, R2 does have an entry for
p.q.r.0/24 in its routing table and thus in every likelyhood the FTN entry
. And then it _can_ put packets for p.q.r.0/24 on the part of the LSP
beyond it. i.e. R2-R3, which come from R4.

Am i missing something?

-abhijit

On Fri, 8 Jun 2001 [email-masked] wrote:

 >     You are correct in your analysis of the problem (the one with R4
 >involved) but there is still a question that needs to be answered. for
 >R2 to be able ro also accept unlabeled packets from R4 and put them on
 >the LSP R1-R2-R3 there has to be a FTN entry created at R2 for say
 >p.q.r.0/24 (which is the LSP R1-R2-R3) where as the trigger for
 >creation of an FTN (DoD or DU) would only be for p.q.0.0/16 as that is
 >the routing update received from R3 which is the next hop for
 >p.q.0.0/16.Thus we are talking of R2 to be able to be smart enough to
 >do traffic merging for two seperate FEC. This can be done but I guess
 >then the intelligence will have to be explicit in terms of - to what
 >level we want to do it (consider another p.0.0.0/8 entry in r2 routing
 >table from a next hop R5 !). You are absolutely right that this is a
 >local issue and does not need to be LSP wide as Eric pointed out that
 >someone having a route to p.q.0.0/16 will surely have a route to
 >p.q.r.0/24 (even if it might not be the best one ;o)
 >
 >regards
 >sumit

---

From: [email-masked]
Date: Fri, 8 Jun 2001 13:48:46 +0530

Nagendra Singh Tomar <[email-masked]> on 06/08/2001 02:00:54 PM

Please respond to [email-masked]

To:   Sumit Chauhan/HSS@HSS
cc:   Nagendra Singh Tomar <[email-masked]>, Abhijit Gadgil
      <[email-masked]>, Eric Gray <[email-masked]>, [email-masked]

Hi sumit!
         Condition 1 in 4.1.4 of RFC 3031 covers the case when the FEC
refers to some directly connected subnet for a node. I can't understand
how u can say that R2 satisfys condition 1. Please explain ??

--tomar

On Fri, 8 Jun 2001 [email-masked] wrote:

>
>
> nagendra!
>      pls find comments inline.
>
> regards
> sumit
>
>
>
>
> Nagendra Singh Tomar <[email-masked]> on 06/08/2001 01:29:02 PM
>
> Please respond to [email-masked]
>
> To:   Abhijit Gadgil <[email-masked]>
> cc:   Sumit Chauhan/HSS@HSS, Eric Gray <[email-masked]>, Nagendra
Singh
>       Tomar <[email-masked]>, [email-masked]
>
A>
>
> Abhijit!
>      Ur proposition leads to a couple of new questions.
> Assume that R2 has no entry for p.q.r.o/24, but for p.q.0.0/16, then
> according to ur proposition R2 will terminate the LSP (LSP1) i.e it will
> act as an egress for LSP1, and from R2 to R3 it will initiate a new LSP
> (LSP2) which will be for FEC p.q.0.0/16 unlike LSP1 which is for
> p.q.r.0/24.
>      The question is why will R2 act as an egress for FEC p.q.r.0/24
> (Refer 4.1.4 RFC 3032 for exact definition of an egress node),
> ***sumit***
> Its RFC 3031 ;o))
> Anyhow nothing in the spec prevents R2 from being the egress as it satisfys
the
> point 1 of the two conditions for being an Egress LSR as follows
>      "   1. R has an address Y, such that X is the address prefix in R's
>             routing table which is the longest match for Y, or"
>
> think of it also as a case where LSR R2 might have been at the edge of an MPLS
> domain. It is not neccessary that R2 is the absolute last router to the FEC
> address prefix for it to act as an LSR.
> ***********
>
> LRq.9 point #1 for DU/DoD Ordered control checks for egress, if the node
> is not egress for FEC it sends a label request for the same FEC
> (p.q.r.0/24) to the nexthop for that FEC (I assume that this nexthop is
> found by doing a longest prefix match in the routing table).
> ****sumit****
> again the R2 shall be marked here as the egress for p.q.r.0/24 as part of the
> "smart" R2 action items.
> *************
> A router is egress for an FEC if it is acting as a "deaggregation" point
> that is its routing table has more precise entries NOT when it is acting
> as an "aggregation" point i.e its routing table has less precise entries (
> as is the case we are discussing)
>
>
> regards
> tomar
>
>
>
>
>
> On Fri, 8 Jun 2001, Abhijit Gadgil wrote:
>
> > sumit,
> >
> --
> ------------------------------------------------------------------------------
>  Nagendra Singh Tomar
>
>  Residence:
>  369 KHB Colony
>  5th Block Koramangala
>  Bangalore 95
>  INDIA
>  Phone : 5524839
>  email : [email-masked]
>
>
> "Sometimes quantity becomes quality"
>                             --Gary Kasparov,
>  When he played against Deep Blue. He said this after looking at a
>  computer which found a forced mate in 249 in an endgame, after calculating
>  all the possible moves with only 5 pieces left on the board.
> ------------------------------------------------------------------------------
>
>
>
>
>
>

--

------------------------------------------------------------------------------
 Nagendra Singh Tomar

 Residence:
 369 KHB Colony
 5th Block Koramangala
 Bangalore 95
 INDIA
 Phone : 5524839
 email : [email-masked]

"Sometimes quantity becomes quality"
                            --Gary Kasparov,
 When he played against Deep Blue. He said this after looking at a
 computer which found a forced mate in 249 in an endgame, after calculating
 all the possible moves with only 5 pieces left on the board.
------------------------------------------------------------------------------

---

From: [email-masked]
Date: Fri, 8 Jun 2001 13:49:26 +0530

hi nagendra!
     yup I am sorry for mis-interpretting  "has an address Y" as "having an
address Y in its routing table". You are right that strictly speaking it cannot
be an Egress LSR. But IMHO I still think, as part of the "smart" LSR theory we
might still safely act as an Egress LSR for the situation discussed. actually
closer to being a Proxy Egress LER (again not strictly by the specs.)

regards
sumit

Hi sumit!

--tomar

Singh
A>
the

--

 Residence:
 369 KHB Colony
 5th Block Koramangala
 Bangalore 95
 INDIA
 Phone : 5524839

---

From: [email-masked]
Date: Fri, 8 Jun 2001 14:17:34 +0530

hi!
     What you are saying is correct tat it is highly improbable but it is not
impossible. The hint for such a topology lies in a scenario where adjoining
routers have MPLS enabled over one of the interfaces connesting them but nowhere
is it essential that they also have an IGP(say OSPF) also enabled on that
interface. I think it is not mandated anywhere in the specs that an MPLS enabled
interface should also have IGP enabled on the same interface. Am i wrong?

regards
sumit

"Vijayanand C" <[email-masked]> on 06/08/2001 02:25:43 PM

cc:   [email-masked]

Subject:  RE: Few questions related to LDP

Hello,
I want to add something regarding this.

The routes you are talking are nothing but the routes maintained by the
routing protocol. Now, within a domain, should'nt the routers have their
routes in sync. Route updates are meant precisely for that purpose. I don't
understand how 2 neighbouring routers have 2 routes of the form p.q.r.0/24,
p.q.0.0/16. This will happen only when the  former is the gateway to the
subnet p.q.r.0/24 and the subnet route is not leaked.  In that case , it
automatically becomes the ingress for p.q.r.0/24. Hence, as Eric says it can
issue an explicit NULL and act as ingress for the FEC p.q.r.0/24. It goes
one level down the heirarchy. p.0.0.0/8 is one level up the heirarchy, it is
outside p.q.0.0/16

Regards,
Vijay

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of
[email-masked]
Sent: Friday, June 08, 2001 10:22 AM
To: Abhijit Gadgil
Cc: Eric Gray; Nagendra Singh Tomar; [email-masked]
Subject: Re: Few questions related to LDP

hi abhijit!
     You are correct in your analysis of the problem (the one with R4
involved)
but there is still a question that needs to be answered. for R2 to be able
ro
also accept unlabeled packets from R4 and put them on the LSP R1-R2-R3 there
has
to be a FTN entry created at R2 for say p.q.r.0/24 (which is the LSP
R1-R2-R3)
where as the trigger for creation of an FTN (DoD or DU) would only be for
p.q.0.0/16 as that is the routing update received from R3 which is the next
hop
for p.q.0.0/16.Thus we are talking of R2 to be able to be smart enough to do
traffic merging for two seperate FEC. This can be done but I guess then the
intelligence will have to be explicit in terms of -  to what level we want
to do
it (consider another p.0.0.0/8 entry in r2 routing table from a next hop R5
!).
You are absolutely right that this is a local issue and does not need to be
LSP
wide as Eric pointed out that someone having a route to p.q.0.0/16 will
surely
have a route to p.q.r.0/24 (even if it might not be the best one ;o)

regards
sumit

Abhijit Gadgil <[email-masked]> on 06/08/2001 05:28:08 AM

To:   Eric Gray <[email-masked]>
cc:   Nagendra Singh Tomar <[email-masked]>, [email-masked] (bcc:
Sumit
      Chauhan/HSS)

Eric,

If R2 is distributing bindings unsolicitedly, it will always distribute
bindings for p.q.0.0/16 and won't distribute for p.q.r.0/24 as it does not
have entry for that FEC in its routing table.

And R2 can send Mapping for label request p.q.r.0/24 when it receives
explicitely such request and in that case it MUST send a No Route
Notification.(according to rfc3036 section 3.5.8).. I accept it is bit
harsh on R2's part in doing so, but this is what the RFC says....

The original question was Whether R2 can put packets from some other guy
R4(pls see below), onto the LSP R1-R2-R3. To which someone has pointed out
that no it can't do so. IMO R2 can do so.. whether it does or not is
implementation choice and standards don't prevent that.

 >   --- R1 --- R2 --- R3 ---
                 |
                 R4

btw there  is a syntax error in ur mail in follwing para. "No matching
brackets". :-)

regards,

-abhijit

 >If R1 requests a label from R2 for the FEC p.q.r.0/24, R2 could return the
 >IPv4 explicit NULL label (indicating that it will egress packets destined
 >for addresses matching this FEC.  In any case, R1's requesting a label
 >R2 was not intended to cause R2 to ingress packets for this FEC (so an
 >FTN would not be created for this FEC, but for different reasons than are
 >indicated in Abhijit's reply).  R2's giving R1 an implicit NULL label for
 >FEC p.q.r.0/24 allows R2 to examine unlabled packets for this FEC and
 >- possibly - assign those packets to an LSP corresponding to the FEC
 >p.q.0.0/16.  For this LSP, R2 could have an FTN and ingress packets.
 >
 >--
 >Eric Gray

---

From: [email-masked]
Date: Fri, 8 Jun 2001 14:56:55 +0530

hi vijay!
     what we were considering was teh traffic coming the other way. The topology
you drew is fine for our interest. But consider te discussion for the flow in
the opposite direction!
ciao
sumit

"Vijayanand C" <[email-masked]> on 06/08/2001 02:55:14 PM

To:   [email-masked]
cc:    (bcc: Sumit Chauhan/HSS)

Hello,

That apart one more issue.

     |domain|----R1--- R2----R3---

If you are talking about the situation where  R1 has only p.q.r.0/24 and R2
has only p.q.0.0/16, then you are not leaking the route p.q.r.0/24 outside
the subnet. Actually in this case p.q.r.0/24 is the address of the
subnetwork which lies to the left of R1. p.q.0.0/16 is the subnet which is
encompassing many such subnets say p.q.r.0/24, p.q.s.0/24 etc.

So at R1 a packet arriving for p.q.r.0/24 ahould be forwarded to the left,
ie, the next hop for this FEC is inside the domain not outside !!

So, R1 will never request a label for p.q.r.0/24 to R2, simply because it is
not the next hop!

One more thing in this case R1 should be having p.q.0.0/16 since it is a
border router for p.q.r.0/24.

YOu have to state clearly your topology/subnert/AS configuration

Regards,
Vijay

-----Original Message-----
From: Vijayanand C [mailto:[email-masked]]
Sent: Friday, June 08, 2001 2:55 PM
To: [email-masked]
Subject: RE: Few questions related to LDP

Hello,

That apart one more issue.

     |domain|----R1--- R2----R3---

If you are talking about the situation where  R1 has only p.q.r.0/24 and R2
has only p.q.0.0/16, then you are not leaking the route p.q.r.0/24 outside
the subnet. Actually in this case p.q.r.0/24 is the address of the
subnetwork which lies to the left of R1. p.q.0.0/16 is the subnet which is
encompassing many such subnets say p.q.r.0/24, p.q.s.0/24 etc.

So at R1 a packet arriving for p.q.r.0/24 ahould be forwarded to the left,
ie, the next hop for this FEC is inside the domain not outside !!

So, R1 will never request a label for p.q.r.0/24 to R2, simply because it is
not the next hop!

One more thing in this case R1 should be having p.q.0.0/16 since it is a
border router for p.q.r.0/24.

YOu have to state clearly your topology/subnert/AS configuration

Regards,
Vijay

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Friday, June 08, 2001 2:18 PM
To: Vijayanand C
Cc: [email-masked]
Subject: RE: Few questions related to LDP

hi!
     What you are saying is correct tat it is highly improbable but it is
not
impossible. The hint for such a topology lies in a scenario where adjoining
routers have MPLS enabled over one of the interfaces connesting them but
nowhere
is it essential that they also have an IGP(say OSPF) also enabled on that
interface. I think it is not mandated anywhere in the specs that an MPLS
enabled
interface should also have IGP enabled on the same interface. Am i wrong?

regards
sumit

Hello,

Regards,
Vijay

-----Original Message-----

hi abhijit!

regards
sumit

Eric,

                 |
                 R4

regards,

-abhijit