Re: [mpls-linux-general] activate label

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On Fri, Jan 21, 2005 at 04:26:33PM +0800, sanjeev ravindran wrote:
> Thank you so much for ur response James,
> As you explained, RSVPTE can have back up LSPs. And currently all the backup LSPs also will be installed in the forwarding plane. But in my perspective, this doesnt serve the actual purpose.. A back up LSP needs to be enabled only when the primary LSP fails.. In this scenario, there needs to be some mechanism where we can bind a label and activate  it later for LSPs. Im not sure if this is a valid point... This is what I feel... 

One this to remember is that installing the LSP into the forwarding plan
and mapping traffic to it are two different steps.  For example I can
create 2 LSPs, but only map traffic to one of them.  So for all intents and
purposes the 2nd LSP is not used for anything.  Only when I maps traffic to
it will it be used.

MPLS Linux provides 3 mechanisms for mapping traffic to a LSP:
-spec_nh system which allow IPv4 or IPv6 routes to be mapped to a LSP
-MPLS tunnel interface represents a LSP as a logical interface.
 The interface can be configured to appear as a PtP interface connected
 to the egress LER
-spec_nh system can be used in combination with iptables (netfilter) to
 map and/or mark specific traffic that will traverse a LSP.

Here is an example of how you could use a MPLS tunnel interface to
facilitate a primary/backup situation.

An ingress LER uses RSVP-TE to signal 2 LSPs which terminate on the same
egress LER, but take two seperate paths through the network.  These LSPs
will be used for for a primary/backup senerio.  The ingress LER uses a
MPLS tunnel interface to map traffic to the primary LSP.  It configured
the MPLS tunnel interface to look like a PtP connection to the egress LER.
At this point traffic destined to the egress LER used the primary LSP.
No traffic will traverse the backup LSP.

If/when the primary LSP breaks, RSVP-TE will receive a path-tear for the
primary LSP.  At that time it will trigger the ingress LER to modify the
MPLS tunnel interface and detattach the primary LSP from the MPLS tunnel
interface and attach the backup LSP to the MPLS tunnel interface (the
process of modifing a MPLS tunnel interface to move from one LSP to another
takes just one system call).  At that point traffic destined to the egress
LER uses the backup LSP.  No traffic will attempt to traverse the primary LSP.

Let me know if this will suit your needs or if you still require more
functionality.

> With best regards,
> Sanjeev R
> 
> 
> 
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> 
> 
> 
> ----- Original Message -----
> From: "James R. Leu" <jl...@mi...>
> To: "sanjeev ravindran" <san...@li...>
> Subject: Re: [mpls-linux-general] activate label
> Date: Thu, 20 Jan 2005 23:14:38 -0600
> 
> > 
> > On Thu, Jan 20, 2005 at 06:34:12PM +0800, sanjeev ravindran wrote:
> > > Thank you for ur response James,
> > >
> > > Ur explanation cleared my doubts regarding the activation of 
> > > labels.. However, i would like to know if the LSP will be 
> > > activated [I mean to say traffic will be forwared] when label 
> > > binding[installation in to the forwarding plane] is done at the 
> > > switch level.
> > > Or is there any way i can bind the label at the switch level but 
> > > still keep it inactive? and i can activate it to forward traffic 
> > > at a later time?
> > 
> > MPLS linux does not currently implement admin status on each MPLS segment.
> > Up till now, I've not seen a need to. I'd be open to implementing it,
> > provided there is a valid application for it.
> > 
> > > Thanks in advance...
> > > With best regards,
> > > Sanjeev R
> > >
> > > ----- Original Message -----
> > > From: "James R. Leu" <jl...@mi...>
> > > To: rameshv <ram...@wi...>
> > > Subject: Re: [mpls-linux-general] activate label
> > > Date: Wed, 19 Jan 2005 09:08:50 -0600
> > >
> > > > > On Wed, Jan 19, 2005 at 04:20:50PM +0530, rameshv wrote:
> > > > > hi,
> > > > >
> > > > > what is meant by activating label, active connection, backup connection ?
> > > > > I believe you are referring to the difference between allocating and
> > > > activating.  Allocation is done in the signaling layer.  Typically
> > > > activation of a label means to install it into the forwarding plane.  For
> > > > example RSVP-TE could signal a backup LSP, meaning allocate and distribute
> > > > labels for the LSP, but it would only install the labels into 
> > > the forwarding
> > > > plane (activate) when the primary LSP fails.
> > > > > (note that the above is a contrived example, all deployed implementations
> > > > of RSVP-TE that signal backup LSPs install them into forwarding plane prior
> > > > to the failure of the primary LSP)
> > > > > > any help is appreciated
> > > > >
> > > > > regards
> > > > > ramesh
> > > > >
> > > > >
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