Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: ~ECMP =>~ETH aggregation?

[Alexander Vainshtein <[e-mail]>]

Curtis, Maarten and all:
My reading of Maarten's comment is like following:

	Y.1731-style packet loss measurement will not work correctly across LAG.

Please note that this is correct in the "pure Ethernet" situation; MPLS-TP does not add anything new here.
I suspect that this was one of the reasons why IEEE has not included performance monitoring mechanisms in 802.1ag; it would be nice if the people that have participated in these discussions could confirm (or disprove) this.

To the best of my knowledge, the only requirement that can be interpreted as a suggestion to use Y.1731-style packet loss measurements is given in  Section 2.2.1 "Packet Loss Measurement" of the MPLS-TP OAM Requirements draft (http://www.ietf.org/id/draft-ietf-mpls-tp-oam-requirements-06.txt):

<quote>
   It SHOULD be possible to rely on user traffic to perform that
   functionality.
<end quote> 

("That functionality" refers to packet loss ration measurement).

Quoting from RFC 2119:

<quote>
3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.
<end quote>

IMHO and FWIW this text ideally applies to usage (or non-usage) of LAG-based Sections in MPLS-TP.

My 2c,
     Sasha

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of Maarten Vissers
Sent: Monday, March 15, 2010 10:09 AM
To: [e-mail]
Cc: [e-mail]
Subject: Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: ~ECMP =>~ETH aggregation?

 
Curtis,

> Using src/dst or label stack based has insures that no microflow
> is reordered (this is important) but does reorder traffic within
> the outer LSP (this doesn't matter).

In a transport network with performance monitoring it **does matter** if
packets with the **same CoS** are forwarded over different links.
Performance monitoring will provide incorrect results in such case.

When you put a Section LSP over a LAG/CL, then there is 1 Section LSP and
performance monitoring will not be functioning. 

The better alternative is to put the set of edge-to-edge LSPs over a LAG/CL
and to use an Ethernet Section 'VLAN' per link. Now there will be many
edge-to-edge LSPs that have to traverse the LAG/CL and those can be
distributed over the links on the basis of their edge-to-edge LSP label
value.

When the the LAG/CL is between PE nodes, then you can use LAG or ACL-SNCG/I
for the set of PW, Service-LSP and transport service layer PST-LSP
connections between two PEs. The distribution is on the basis of PW,
service-LSP or PST-LSP label values in this case.

A further alternative is to disable performance monitoring of the
edge-to-edge LSPs. When this is done, then it is possible to do LAG/CL
between two P nodes on the basis of the PW, service-LSP and PST-LSP label
values. The performance monitoring in the transport service layer
connections is not impacted by this approach. 

Regards,
Maarten

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] 
Sent: zondag 14 maart 2010 6:12
To: Maarten Vissers
Cc: [e-mail]; [e-mail]
Subject: Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: ~ECMP
=>~ETH aggregation?


In message <005601cabe98$d2783480$[e-mail]>
Maarten Vissers writes:
>  
> Curtis,
>  
> MPLS-TP and other packet transport technologies can be run over a 
> compound link. Such compound link can be provided by multiple section 
> layer transport paths or by multiple edge-to-edge LSPs. In both cases 
> the nodes at the edge of such compound link have to make sure that all 
> traffic within a service/transport path is transported via only one 
> link within the compound link. This to maintain e.g. the order of 
> packets/frames within the service/transport path.
>  
> To deploy the survivability provided by compound links, ITU-T Q.9/15 
> has developed the Adaptive Compound Link SubNetwork Group protection 
> with Inherent monitoring (ACL-SNCG/I) mechanism. This ACL-SNCG/I 
> protection controls the distribution of 1) PWs, service-LSPs and 
> service path layer PST LSPs over a service path layer component links 
> (supported by edge-to-edge LSPs) within a compound link, 2) 
> edge-to-edge LSPs and transport path layer PST LSPs over a transport 
> path layer component links (supported by sections)within a compound 
> link .
>  
> The initial work done assumed the presence of non-adaptive media, 
> which would cause a component link to be completely available or 
> completely unavailable (as in ethernet LAG). At the moment this work 
> is being extended to also support adaptive media, which are able to 
> reduce their bandwidth to a lower level; i.e. creating a partly 
> available state in between the original two states.
>  
> Input to the distribution process is the CIR(EIR) and relative 
> priority of each service path or transport path that is carried over 
> the compound link and the available bandwidth of each component link 
> within the compound link.  The distribution process computes the 
> distribution of the service paths, or transport paths. If the 
> bandwidth of the compound link becomes too small to support all, then 
> the lowest priority service/transport paths are blocked and 
> packets/frames of those paths are not longer forwarded over the 
> compound link.
>  
> A service path or transport path's bandwidth must always be smaller 
> then the bandwidth of the component links.
>  
> Regards,
> Maarten


Maarten,

Thank you for reminding me that the ITU is ignoring reality.  That is
nothing new though.

 ->    Input to the distribution process is the CIR(EIR)

The reality is that when LSP hierarchy is used (to reduce the number of
labels and reduce the amount of signaling that needs to occur on a fault and
in doing so improve scaling) or when MPLS is applied to a small high
bandwidth core, the LSPs are signaled with BW values that are greater than
the size of a single LAG/CL member.  This is where src/dst or label stack
based hash has worked very well for about a decade.  This information is not
in the signaling of the outer LSP.

Using src/dst or label stack based has insures that no microflow is
reordered (this is important) but does reorder traffic within the outer LSP
(this doesn't matter).

Curtis


> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On 
> Behalf Of Curtis Villamizar
> Sent: vrijdag 5 maart 2010 6:51
> To: Adrian Farrel
> Cc: [e-mail]; Rui Costa
> Subject: Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: 
> ~ECMP =>~ETH aggregation?
>  
>  
> In message <21AFCCB59EFE4816B26E280DF3355CE2@your029b8cecfe>
> "Adrian Farrel" writes:
> >  
> > Surely the formation of the server layer and the use of OAM within 
> > the server layer is entirely an issue for the server layer.
> >  
> > It is a mistake for the MPLS-TP layer to be aware of the underlying 
> > technology that provides the link connectivity between to adjacent 
> > LSRs. The links provided by the server layer have certain resiliency 
> > and recovery properties, as well as properties associated with 
> > in-order (or not) packet delivery that are announced to the MPLS-TP 
> > network (usually through
> > configuration) and the MPLS-TP network can choose which links to use 
> > accordingly.
>  
> The goal is to make OAM work by adding entropy.  If there is no 
> underlying LAG, then the entropy serves no purpose but does no harm.
>  
> If there is an underlying LAG then not having entropy allows the OAM 
> traffic to test only one member.  For example, if an MPLS LSP hop
> (section) is a LAG, traffic within that MPLS LSP would take different 
> LAG members if the entire label stack was not the same for all traffic 
> or if the LSP carried IP traffic from more than one host pair.  If the 
> OAM traffic had a fixed label stack it would test only one LAG member.
>  
> > LAG at a server Ethernet layer is a way of providing a composite 
> > link to the MPLS-TP layer. That link has specific properties, but 
> > the MPLS-TP layer cannot be expected to take specific measures to 
> > operate the link. That is the job of the server layer itself (noting 
> > that the adaptation into the LAG is a function of the server layer, 
> > just as the
> operation).
>  
> If CL is allowed for MPLS-TP, then OAM must work for CL.  We should 
> not knowingly just specify something that is broken.
>  
> > So, the MPLS-TP layer runs OAM across the link. It doesn't know how 
> > the link is formed. It is the responsibility of adaptation function 
> > to either distribute the MPLS-TP packets across the group members 
> > such that link degradation will be noticed by the MPLS-TP layer 
> > (this could be noted as a requirement that the MPLS-TP layer puts on 
> > the server layer that link degradation should be detectable by any 
> > measure of MPLS-TP packets); or the server layer must perform its 
> > own OAM to detect link degradation and report it to the MPLS-TP 
> > layer at the link end
> points.
>  
> For plain old MPLS, it doesn't know about any LAG either, but the 
> 127.x source addresses add the entropy needed to provide effective 
> OAM.  That is why IETF specified MPLS Ping and and rejected 1711 and 
> why MPLS Ping works and 1711 doesn't work.
>  
> > LAG is not the only "complex" way of forming links in the MPLS-TP 
> > network from multiple links in the server network, and we really 
> > don't want to embark on making MPLS-TP understand each and every 
> > server
> technology.
> >  
> > Cheers,
> > Adrian
>  
> However, any method which is capable of supporting an LSP that is 
> greater in capacity than any one component link needs to look below 
> the top label to do so.  I think that is trivailly provable given that 
> the top level is always the same for that LSP.
>  
> Therefore no matter what we define CL to be, if this CL supports LSP 
> of greater than a LAG member size, a capability we currently have with 
> Ethernet LAG or ECMP over parallel links (another form of link 
> aggregation that predates Ethernet LAG by over a decade), then OAM 
> needs to provide entropy to insure that any CL/LAG/ECMP along the path is
exercised.
>  
> Curtis
>  
>  
> > ----- Original Message -----
> > From: "Stewart Bryant" <[e-mail]>
> > To: <[e-mail]>
> > Cc: "Rui Costa" <[e-mail]>; <[e-mail]>
> > Sent: Wednesday, March 03, 2010 10:59 AM
> > Subject: Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: 
> > ~ECMP => ~ETH aggregation?
> >  
> >  
> > > Curtis Villamizar wrote:
> > >> In message <[e-mail]> Stewart Bryant writes:
> > >>
> > >>>  I would think that if the operator wanted the bandwidth more 
> > >>> than they wanted the fate sharing, they will deploy the technology.
> > >>>  - Stewart
> > >>>
> > >>
> > >>
> > >> There is no reason not to put some entropy in the extension to 
> > >> MPLS Ping so that there was fate sharing over LAG.
> > >>
> > >> Curtis
> > >>
> > >>
> > > Curtis
> > >
> > > Do you have some text in mind?
> > >
> > > - Stewart
> > > _______________________________________________
> > > mpls-tp mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/mpls-tp
>  
> _______________________________________________
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