The MPLS-OPS Archive

["Akhilesh" <akhilesh@trinc.com>]

Hi Matthew

If you want to implement PHP, then LDP running in the control plane should
give IMPLICIT NULL LABEL (by LER to its Upstream) in label mapping msg.  I
had also wrote in my previous mail that
> > In PHP, Egress(LER) will give IMPLICIT NULL LABEL in label
> > mapping msg to
> > its Upstream LSR(Penultimate Hop) .  As, this LSR has
> > IMPLICIT NULL LABEL as
> > a out label, it will blindly pop the Label stcak entry, and forwards
> > remaining packet to the LER.
Else in other case (non PHP) LER will give EXPLICIT NULL LABEL in its label
mapping msg to its Upstream. and upstream will insert this EXPLICIT NULL
LABEL in its SHIM Header and forwards packet to LER. Now this Explicit Null
Label is In Label for LER, so it will simply pop the label stack entry and
forward the packet based on IP header.

Hope that i helped.  suggestions are welcome.

Thanks
Akhilesh Yede
www.trinc.com

----- Original Message -----
From: Matthew Beggs <Matthew.Beggs@hutchison3g.com>
To: 'Akhilesh' <akhilesh@trinc.com>; Leticia Cozart
<lcozart@technicacorp.com>; <mpls-ops@mplsrc.com>
Sent: Thursday, September 27, 2001 12:49 PM
Subject: RE:


> Hi there,
>
> If you say PHP is an optional feature, what do I need to do to tell the
> network to implement it rather letting the LER perform this function ?
>
> Regards
>
> Matthew Beggs
>
> > -----Original Message-----
> > From: Akhilesh [mailto:akhilesh@trinc.com]
> > Sent: 25 September 2001 17:00
> > To: Leticia Cozart; mpls-ops@mplsrc.com
> > Subject: Re:
> >
> >
> > Leticia
> >
> > Penultimate Hop Popping (PHP) is the optional implemetation
> > in MPLS.  Using
> > PHP, v can reduce the overhead of the LERs.
> > In PHP, Egress(LER) will give IMPLICIT NULL LABEL in label
> > mapping msg to
> > its Upstream LSR(Penultimate Hop) .  As, this LSR has
> > IMPLICIT NULL LABEL as
> > a out label, it will blindly pop the Label stcak entry, and forwards
> > remaining packet to the LER.
> >     If one does not do PHP, then when the LSP egress receives
> > a packet,   it
> > first looks up the top label, and determines as a result of
> > that  lookup
> > that it is indeed the LSP egress.  Then it must pop the
> > stack,   and examine
> > what remains of the packet.  If there is another label on
> > the stack, the
> > egress will look this up and forward the packet based on this
> > lookup.  (In
> > this case, the egress for the packet's level m LSP is also an
> > intermediate
> > node for its level m-1 LSP.)  If there is  no other label on
> > the stack, then
> > the packet is forwarded according  to its network layer
> > destination address.
> > Note that this would  require the egress to do TWO lookups,
> > either two label
> > lookups or a label lookup followed by an address lookup.
> >
> > Cheers
> > Akhilesh Yede
> > Hyderabad, India.
> >
> > ----- Original Message -----
> > From: Leticia Cozart <lcozart@technicacorp.com>
> > To: <mpls-ops@mplsrc.com>
> > Sent: Tuesday, September 25, 2001 5:35 PM
> >
> >
> > > Hello-
> > >
> > > Is anyone familiar with the term Penultimate Hop Popping?
> > What is its
> > > purpose?
> > >
> > > Thanks!
> > >
> > > Leticia...
> > >
> > >
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