The MPLS WG Archive

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Giles,

> -----Original Message-----
> From: Giles Heron [mailto:giles@packetexchange.net]
> Sent: Thursday, December 13, 2001 5:48 AM
> To: Don Fedyk
> Cc: Ben Mack-Crane; neil.2.harrison@bt.com; mpls@UU.NET
> Subject: Re: MPLSOAM BOF meeting draft minutes
> 
> 
> > Don Fedyk wrote:
> > 
> > Giles
> > 
> > Semi broken boxes was the reason that LSP Ping was introduced.
> 
> Agreed.
> 
> But why was MPLS OAM introduced?  If we are only addressing 
> the problem
> of semi-broken boxes then do we need to be constantly monitoring all
> LSPs?

Yes, because you never know when the break will show up. Or are you suggesting
that we wait for customer complain?

> 
> Again, I would compare this to IP networks.  In the IP case we don't
> send pings constantly to every prefix in our networks to 
> check that they
> are still reachable, so I'm not 100% convinced we should be 
> sending CVs
> constantly in MPLS?

The reason is that in IP networks you have hop-by-hop routing. So if a
router's routing table is corrupted, the next hop can send the packet in the
right direction.. While in MPLS, a single forwarding error can send traffic
all the way to the wrong destination.

-Shahram

> 
> > Seems like we disagree on how small that niche is.
> 
> looks like it :)
> 
> Giles
>  
> > Don
> > 
> > > -----Original Message-----
> > > From: Giles Heron [mailto:giles@packetexchange.net]
> > > Sent: Wednesday, December 12, 2001 1:34 PM
> > > To: Fedyk, Don [BL60:1A00:EXCH]
> > > Cc: Ben Mack-Crane; neil.2.harrison@bt.com; mpls@UU.NET
> > > Subject: Re: MPLSOAM BOF meeting draft minutes
> > >
> > >
> > > agreed - since IP doesn't have LSPs :)
> > >
> > > but I'm not sure how relevant that is?
> > >
> > > As far as I can tell MPLSOAM only protects against semi-broken
> > boxes.
> > > That seems like a pretty small niche?
> > >
> > > Giles
> > >
> > > > Don Fedyk wrote:
> > > >
> > > > But IP does not have a per LSP stateful control plane.
> > > >
> > > > Don
> > > >
> > > > > -----Original Message-----
> > > > > From: Giles Heron [mailto:giles@packetexchange.net]
> > > > > Sent: Wednesday, December 12, 2001 1:14 PM
> > > > > To: Ben Mack-Crane
> > > > > Cc: neil.2.harrison@bt.com; mpls@UU.NET
> > > > > Subject: Re: MPLSOAM BOF meeting draft minutes
> > > > >
> > > > >
> > > > > agreed - within one router control and data follow
> > > different paths.
> > > > >
> > > > > But the same is true for IP.
> > > > >
> > > > > Giles
> > > > >
> > > > > Ben Mack-Crane wrote:
> > > > > >
> > > > > > As far as I know, the control path and data path are
> > > not entirely
> > > > > > convergent for MPLS.  The control packets do not follow the
> > same
> > > > > > data path through a router as the data packets, and thus
> > > > > are not subject
> > > > > > to the same failures.
> > > > > >
> > > > > > Regards,
> > > > > > Ben
> > > > > >
> > > > > > Giles Heron wrote:
> > > > > > >
> > > > > > > neil.2.harrison@bt.com wrote:
> > > > > > > [snip]
> > > > > > > > If one agrees to the fact that these (OAM functions) are
> > > > > > > > present/valid/required in SDH etc and hence in GMPLS,
> > > > > then one should not
> > > > > > > > argue that they don't apply to other CO technologies.
> > > > > An ER/signalled p2p
> > > > > > > > LSP is a trail, in G.805 parlance, irrespective of
> > > > > whether wants to try and
> > > > > > > > camouflage this fact or not...and so the same
> > > > > principles apply.  You can't
> > > > > > > > argue it both ways IMO.
> > > > > > > > <snipped to end>
> > > > > > >
> > > > > > > I'm not sure I agree with this conclusion.
> > > > > > >
> > > > > > > isn't one key difference between SDH/GMPLS etc. and MPLS
> > > > > the fact that
> > > > > > > for an MPLS LSP the control plane is convergent with the
> > > > > data plane?
> > > > > > > Sure for TE LSPs the LSP path isn't generally convergent
> > > > > with the IGP,
> > > > > > > but it is convergent with the RSVP-TE control traffic.
> > > > > > >
> > > > > > > Giles
> > > > > > >
> > > > > > > --
> > > > > > >
> > > > 
> =================================================================
> > > > > > > Giles Heron    Principal Network Architect    
> PacketExchange
> > 
> > > > Ltd.
> > > > > > > ph: +44 7880 506185              "if you build it 
> they will
> > > > yawn"
> > > > > > >
> > > > 
> =================================================================
> > > > >
> > > > > --
> > > > >
> > =================================================================
> > > > > Giles Heron    Principal Network Architect    PacketExchange
> > Ltd.
> > > > > ph: +44 7880 506185              "if you build it they will
> > yawn"
> > > > >
> > =================================================================
> > > > >
> > >
> > > --
> > > =================================================================
> > > Giles Heron    Principal Network Architect    PacketExchange Ltd.
> > > ph: +44 7880 506185              "if you build it they will yawn"
> > > =================================================================
> > >
> 
> -- 
> =================================================================
> Giles Heron    Principal Network Architect    PacketExchange Ltd.
> ph: +44 7880 506185              "if you build it they will yawn"
> =================================================================
>