The MPLS WG Archive

[Eric W Gray <ewgray@mindspring.com>]

Yes, that has been suggested as a logical extension of the 'Pipe'
model in DiffServ.  I don't recall where that effort is at right now
but I don't think the work has been adopted by either the MPLS
or CCAMP working groups.  Do you know?

--
Eric Gray

Ray Qiu wrote:

> There is also an option that we don't copy the MPLS TTL back to IP TTL.
> It makes IP think the MPLS LSP is only one hop.
>
> Thanks,
> Ray
>
> On Tue, 21 Aug 2001, Eric W Gray wrote:
>
> > Date: Tue, 21 Aug 2001 13:10:17 -0400
> > From: Eric W Gray <ewgray@mindspring.com>
> > To: Alexander Marhold <alexander@marhold.at>,
> >      MultiProtocol Label Switching Mailing List <mpls@UU.NET>
> > Subject: Re: Time to live
> >
> > Below, the last sentence was supposed to be "Note that Frame
> > Relay ..."
> >
> > --
> > Eric Gray
> >
> > Eric W Gray wrote:
> >
> > > Alexander,
> > >
> > >     No cigar.  The distinction is not cell verses frame, but rather
> > > whether or not it is possible to incorporate the label in the L2
> > > encapsulation.  Where this is possible, ATM and FR, there is
> > > no TTL capability in the L2 encapsulation.  Not that Frame
> > > Relay is Frame based...
> > >
> > > --
> > > Eric Gray
> > >
> > > You wrote:
> > >
> > > > Hello
> > > > I want to explain the mechanism a little bit more in detail
> > > >
> > > > FRAME based general:
> > > > 1. normally at the ingress LSR the IP-TTL is copied into the TTL-field of
> > > > the label header.
> > > > 2. the label-TTL is decremented at each hop by 1
> > > > 3. when it reaches 0 the labelled packet will be dropped and a
> > > > TTL-exceeded-ICMP message will be sent if possible
> > > > 4. at the egress the label-TTL is copied back into the IP-TTL
> > > >
> > > > CELL based general:
> > > > 1. normally at the ingress LSR the IP-TTL is copied into the TTL-field of
> > > > the label header.
> > > > 1a. the ingress LSR to the ATM-MPLS cloud either decrements the TTL by 1
> > > > 1b              or by the amount of ATM_MPLS hops of the LSP ( this he knows from the
> > > > LSP-setup using downstream on demand label allocation and ordered
> > > > lsp-control label setup)
> > > > 2. then the packet is chopped into cells
> > > > 3. the egress reassembles the packet and copies the label ttl back into the
> > > > IP-TTL
> > > >
> > > > if 1a is used then the ATM-MPLS cloud looks like a 1-hop network
> > > >
> > > > special features:
> > > > a) on cisco LSRs there is the possibility to disable the copying of the
> > > > IP-TTL to the label-TTL and the label-TTL again starts at 255.
> > > > on the egress the smaller of the 2 TTL-values ( label and IP-header) will be
> > > > used for the IP-TTL
> > > > then for traceroute the MPLS cloud looks like a 1-hop (2-hop with PHP)
> > > > network
> > > >
> > > > with best regards
> > > >
> > > > Alexander
> > > >
> > > > __/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/
> > > >      __/
> > > >     __/   Dipl.Ing. Alexander Marhold MBA
> > > >    __/   CCIE #3324, CCNP, CCDP, CCSI #20642
> > > >   __/   Core & IP Services <Senior Consultant>
> > > >  __/   Mobile: ++43-(0)664-16 28 234
> > > > __/   PRO IN http://www.proin.com
> > > >
> > > > -----Original Message-----
> > > > From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of
> > > > Asim.Khan@vf.vodafone.co.uk
> > > > Sent: Tuesday, August 21, 2001 6:22 PM
> > > > To: c-david.escobar@wcom.com
> > > > Cc: mpls@UU.NET
> > > > Subject: RE: Time to live
> > > >
> > > > It stays the same. The routers only look at the label value not the IP
> > > > header. When the packet leaves MPLS domain then the normal operation would
> > > > apply.
> > > >
> > > > Asim
> > > >
> > > > -----Original Message-----
> > > > From: David Escobar [mailto:c-david.escobar@wcom.com]
> > > > Sent: 21 August 2001 17:19
> > > > To: mpls@UU.NET
> > > > Subject: Time to live
> > > >
> > > > Hi;
> > > > What happens to the TTL field in the IP header when a labeled packet goes
> > > > through an LSP? Is it decreased at each router or stay the same?
> >