Subject: RE: RSVP LSP

From: Guy Davies <[email-masked]>
Date: Wed, 2 Aug 2000 16:12:37 +0100

Hi Ted,

Erm, I'm not really sure because your restatement is a bit confusing.  To
restate what I said...

You can use a statically configured LSP from A to B.  In this case, you
statically configure A, LER1, LSR and LER2 with the details of the LSP.  NO
Signalling is required since all the configuration is static.  This is
entirely separate from the RSVP signalled tunnel from LER1 to LER2.  This is
two totally isolated LSPs.

You can use an LDP signalled LSP from A to B.  This is identical to the one
above except that you use LDP instead of statically configuring all the hops
along the path.

If your LERs support label stacking, you can configure an LSP from A to B
where the RSVP signalled path from LER1 to LER2 is used as a "single hop" so
the path would appear to be A - LER1 - LER2 - B.

Regards,

Guy

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> Sent: Wednesday, August 02, 2000 2:56 PM
> To: [email-masked]
> Cc: [email-masked]; [email-masked]
> Subject: RSVP LSP
> 
> 
> 
> Hi,
> 
> Thanks for your answer.
> 
> In (1) case, you mean two diffrent LSPs. I understand one is 
> of LDP signaling, the second is of RSVP signaling. Is that right? 
> 
> If the LSP from A to B is LDP signalled, then it should use 
> label stack at case (2), is that right?
> 
> In case (2), is LER1(LIR, Edward says) configured not use 
> RSVP signaling?  
> 
> Is that possible that a whole LSP is composed with two parts, 
> one is LDP signalled, and one is RSVP signalled?
> 
> 
> Thanks in advance
> Ted
> Guy Davies <[email-masked]> wrote:
> >
> > Hi,
> > 
> > Let's assume that there is already an RSVP signalled LSP 
> from LER1 to LER2
> > and, as you've stated, A and B don't speak RSVP (at least 
> on the interfaces
> > to LER1 and LER2 respectively).  There are two possibilities.
> > 
> > 1: You statically configure/LDP signal an LSP right from A 
> to B.  This is
> > totally independent of the existing, RSVP signalled LSP 
> from LER1 to LER2
> > and (if you use LDP to signal the path) requires LER1, LSR 
> and LER2 to
> > understand LDP in addition to RSVP.  In this case, you have 
> two LSPs between
> > LER1 and LER2, one of which extends right out to A and B.
> > 
> > 2: You configure an LSP from A to B using the LSP from LER1 
> to LER2 to make
> > that "hop".  In that case, you require label stacking.  
> i.e. you push a
> > label at A and transmit to LER1, you push a second label at LER1 and
> > transmit to LSR, you swap/pop the top label at LSR and 
> transmit to LER2, you
> > pop the top label (if it's still there) and swap/pop the 
> bottom label at
> > LER2 then transmit to B.  At B, you pop the bottom label 
> (if it's still
> > there) and forward the packet using IP.  In this case, you 
> have a single LSP
> > from LER1 to LER2.  It just happens to be "carrying" 
> another LSP.  This is
> > analogous to an ATM VP.
> > 
> > In 2, the swap/pop decision is based on whether penultimate 
> hop popping is
> > configured.
> > 
> > Finally, remember that you'll have to configure a reverse 
> path LSP to carry
> > the return traffic (B to A) since LSPs are unidirectional.
> > 
> > Regards,
> > 
> > Guy
> > ---
> > Guy Davies              Telindus K-NET Ltd
> > IP Architect            Hatchwood Place, Farnham Road, 
> > e: [email-masked] Odiham, Hants, RG29 1AB
> > t: +44 (0)1256 709285  f: +44 (0)1256 709210  m: +44 (0)7879 434214
> > 
> > 
> > > -----Original Message-----
> > > From: Edward Brookhouse [mailto:[email-masked]]
> > > Sent: Tuesday, August 01, 2000 9:38 PM
> > > To: [email-masked]; [email-masked]
> > > Subject: Re: 
> > > 
> > > 
> > > Just making sure I understand the scenario, do you mean 
> that you are
> > > stitching the two LSP's together across and LSR?
> > > 
> > > If not, would this be more like...
> > > 
> > > A - LIR-TLSR-LER-B
> > > 
> > >     LIR= Label Ingress Router
> > >    TLSR=Transit Label Switch Router
> > >     LER=Label Egress Router
> > > 
> > > Just making sure I caught what you were asking.
> > > 
> > > Edward Brookhouse
> > > Greenwich Technology Partners
> > > [email-masked]
> > > 
> > > 
> > > ----- Original Message -----
> > > From: <[email-masked]>
> > > To: <[email-masked]>
> > > Sent: Tuesday, August 01, 2000 2:07 PM
> > > 
> > > 
> > > > Hi,
> > > >
> > > > I have a question about RSVP LSP:
> > > >
> > > > if we have a LSP like below:
> > > >
> > > > A--LER1--LSR--LER2--B
> > > >
> > > > A,B are none rsvp nodes. LER1, LSR and LER2 are RSVP nodes.
> > > > if LSP is setup from A to B, what happened to LER1, LSR 
> and LER2?
> > > >
> > > > Is there a RSVP LSP established from LER1 to LER2? or they 
> > > just forward
> > > sessions without another RSVP LSP setup?
> > > >
> > > >
> > > > Thanks in advance
> > > > John
> > > >
> > > > ----------
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