From: CCIESP (voicelab@gmail.com)
Date: Thu Aug 18 2005 - 18:38:53 GMT-3
Hi :
3)POP operation in Label Stack : Incoming packet has stack of labels and top
most label will be poped( Removed ) . Exp bit on topmost label will be
copied to topmost label( next-level label ) on the outgoing interface . This
behavior can be changed using set commands discussed above .
should be :
3)......................... Exp bit on topmost label will NOT be
copied to topmost label( next-level label ) on the outgoing interface . This
behavior can be changed using set commands discussed above .
according to :
http://www.cisco.com/en/US/tech/tk436/tk428/technologies_tech_note09186a008022ad7e.shtml
On 8/18/05, Arun Arumuganainar <aarumuga@hotmail.com> wrote:
> Hi ,
>
> > What I have not being able to understand is how my set MPLS EXP bits will
> be
> > carried to the other PEs ?
> > Will I need to apply any service policy to carry MPLS EXP bits from PE to
> > the other ?
> >
>
> By default . DSCP or IP Prec or Dot1Q COS will be automatically copied to
> MPLS EXP !!! No configuration is needed for doing this .
>
> However if you want to change behavior you will have create policy map and
> apply it on the input or output interface using service policy command .
>
> There are two set command available for use in your policy map !!!
>
> a) set mpls exp topmost : This will set exp for topmost label .
> b) set mpls exp imposition : This will set exp bits in the entire label
> stack .
>
> Also it will be interesting to understand how various MPLS operations
> affects your exp values . Basically there are four variants of MPLS
> operations .
>
> 1) Label Imposition : This happens in IP-MPLS boundaries . Default : DSCP
> /IP Prec is copied . The behavior can be changes using set commands in a
> policy map
>
> 2) Label Swap : This happens in MPLS to MPLS path . Here incoming label is
> swapped with outgoing label . Default : EXP bit of incoming label is copied
> to outgoing label's EXP . This behavior can be changed using set commands
> discussed above
>
> 3)POP operation in Label Stack : Incoming packet has stack of labels and top
> most label will be poped( Removed ) . Exp bit on topmost label will be
> copied to topmost label( next-level label ) on the outgoing interface . This
> behavior can be changed using set commands discussed above .
>
> 4) PHP POP operation : Incoming packet has a single label and Label will be
> removed as we forward the Packet . Here EXP will be fully lost . By default
> it is not copied on to DSCP or IP-Prec back !!!
>
> This is a special case where in end to end QoS policies implementation based
> on exp is not possible . However you can work around this situation via two
> methods.
>
> a) Signaling explicit null between PHP LSR and Egress LSR . When explicit
> nul is done then PHP-POP( case 4) operation will be changed to Label Swap
> ( case 2) Hence Problem can be worked around ,
>
> b) Use policy map to mark discard class( one discard class for each exp
> values ) in the incoming interface of PHP router and use policies based on
> Discard class on the output interface !!!
>
> Based on your need you can employ any of the techniques for achieving the
> QoS in MPLS VPN environment .
>
> Hope this helps .
>
> Thanks and Regards
> Arun
> ----- Original Message -----
> From: "Zahid Hassan" <zhassan@gmx.net>
> To: "C&S GroupStudy" <comserv@groupstudy.com>; "R&S CCIE GroupStudy"
> <ccielab@groupstudy.com>
> Sent: Thursday, August 18, 2005 3:54 AM
> Subject: QOS for MPLS VPNs
>
>
> > Dear All,
> >
> >
> > I would be really grateful if someone could suggest or
> > propose any config for implementing QOS for MPLS VPNs.
> >
> > I have the following scenario:
> >
> > CE1 -->PE1-->PE2-->CE2
> >
> > I understand that it is possible to mark and match DSCP and MPLS EXP bits
> as
> > follows:
> >
> > DSCP (CE1)-->EXP(PE1)--->EXP(PE2)--->DSCP(CE2)
> >
> > I am being able to match DSCP bits from CE on PE and apply whatever
> policing
> > required.
> > I can also set MPLS EXP bits on PE according to matched DSCP bits from CE.
> >
> > What I have not being able to understand is how my set MPLS EXP bits will
> be
> > carried to the other PEs ?
> > Will I need to apply any service policy to carry MPLS EXP bits from PE to
> > the other ?
> >
> >
> > Regards,
> >
> > Zahid
> >
> > _____________________________________________________________________
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>
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