Re: [Mpls-interop] MPLS over MPLS-TP

[hejia 48726 <[e-mail]>]

Hi Andy,
   I guess what you suggest by using "a label stack with two EOS bits set" to realize demarcation was once discussed in MPLS over T-MPLS scenario(ITU-T contribution),as a alternative of PW way (which is valid, but not efficient). But the whole idea was not accepted at that time beacause this was claimed to invalid the existing MPLS architecure. :(



B.R.
Jia

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----- 原邮件 -----
发件人: "Malis, Andrew G. (Andy)" <[e-mail]>
日期: 星期四, 十二月 11日, 2008 下午9:51
主题: Re: [Mpls-interop] MPLS over MPLS-TP
收件人: Adrian Farrel <[e-mail]>
抄送: [e-mail]

> Adrian,
> 
> Thanks for the clarification, but doesn't change my points about
> generality of the MPLS-TP service.
> 
> Thanks,
> Andy
> 
> -----Original Message-----
> From: Adrian Farrel [mailto:[e-mail]] 
> Sent: Thursday, December 11, 2008 8:40 AM
> To: Malis, Andrew G. (Andy)
> Cc: [e-mail]
> Subject: Re: [Mpls-interop] MPLS over MPLS-TP
> 
> Thanks Andy,
> 
> Just one point.
> My understanding of the PW usage is that an EOS has to be present.
> That means that the choice (when there is demarcation) is between 
> PW and
> no 
> PW. EOS would always be there.
> 
> A
> ----- Original Message ----- 
> From: "Malis, Andrew G. (Andy)" <[e-mail]>
> To: "Adrian Farrel" <[e-mail]>uk>; "Drake, John E" 
> <[e-mail]>om>; "Ben Niven-Jenkins" 
> <[e-mail]>om>; <[e-mail]>
> Sent: Thursday, December 11, 2008 1:30 PM
> Subject: RE: [Mpls-interop] MPLS over MPLS-TP
> 
> 
> Adrian,
> 
> Thanks for taking the discussion in Geneva to the list. I have some
> comments inline.
> 
> Cheers,
> Andy
> 
> -----Original Message-----
> From: [e-mail]
> [mailto:[e-mail]] On Behalf Of Adrian Farrel
> Sent: Thursday, December 11, 2008 5:35 AM
> To: Drake, John E; Ben Niven-Jenkins; [e-mail]
> Subject: Re: [Mpls-interop] MPLS over MPLS-TP
> 
> Hi,
> 
> We have had considerable debate about this in Geneva.
> (I think it is probably time to take this discussion to mpls-tp, 
> so I
> will
> recreate the thread there).
> 
> Some data points for this discussion are:
> 
> 1. What is the service provided by an MPLS-TP network?
> Is it (as described in some documents) the provision of 
> pseudowires over
> an
> MPLS transport network?
> Or is it the provision of services (including pseudowires) over an 
> MPLStransport network?
> 
> AM> My preference is the latter - it should be more general than just
> the provisioning of pseudowires (even if we have IP and MPLS
> pseudowires). A PW is an instance of a label in the stack, and 
> what can
> be transported over MPLS-TP shouldn't be limited to just that 
> instance.
> 2. It there a need to provide demarcation between server traffic and
> client
> traffic?
> There seem to be several reasons why one might do this:
> a. architectural beauty
> b. consistency with the answer to point 1
>   (depending on the answer!)
> c. ease of OAM and general management
>  (so you can see the demarcation when you sniff the network)
> d. To avoid accidental misforwarding of traffic
>  For example, consider an MPLS-TP network operated using
>  the management plane. In this network it is possible that an
>  LSR along the path of an LSP is misconfigured to pop the
>  MPLS-TP LSP top label. If what is found underneath is
>  either a label from the client label space, or is treated as a label
>  (in the case where the payload is IP) we will not spot an error,
>  but may misforward traffic.
> 
> AM> Yes, we need a clear demarcation, for reasons c and d. Here in VZ,
> our current discussions are around using IP/MPLS as an overlay over
> MPLS-TP, with different groups in charge of the management of each
> layer, thus maintaining our current layer separation. Plus in the 
> futurewe may wish to offer MPLS-TP as a customer-facing interface, 
> withcustomers using it to interconnect their own IP/MPLS routers.
> 
> 3. If there is demarcation as suggested in point 2, what is the 
> best way
> to
> provide demarcation?
> a. Encode as a PW with the end of stack set and a PW header 
> according to
> the
> appropriate PW encoding type.
> b. Simply use the end of stack bit to say that we have reached the
> bottom of
> the MPLS-TP label stack.
> (The alternative clearly being that the label stack runs through from
> the
> client label stack to the server label stack.)
> 
> AM> I prefer b, for simplicity and generality of what can be carried
> over MPLS-TP. Thus we could have a label stack with two EOS bits set.
> 
> AM> Also, regarding the possible misconfiguration discussed in 
> question2, this could happen with PW labels as easily as with non-
> PW labels, so
> requiring PWs to be used with MPLS-TP is no panacea. Rather, this sort
> of misconfiguration needs to be detected using OAM and other MPLS-TP
> layer management mechanisms.
> 
> Cheers,
> Andy
> 
> 
> 
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