The MPLS-OPS Archive

[Matthew Beggs <Matthew.Beggs@hutchison3g.com>]

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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