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neil.2.harrison | 1 Jun 2002 01:14
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RE: Basic LDP Question

Shahram Davari wrote 31 May 2002 19:40
> To: 'Yakov Rekhter'
> Cc: Giles Heron; 'mpls <at> uu.net'; 'ppvpn <at> ppvpn.francetelecom.com'
> Subject: RE: Basic LDP Question 
> 
> 
>  
> > > in IP also you can do ACL.
> > 
> > yes, but it has its own cost/complexity.
> 
> Sure, but using LDP you are forced to run some kind of OAM, to detect
> mis-config of LSRs. So nothing is gained. The cost/complexity 
> of filtering is
> replaced with cost/complexity of OAM.
> 
> -Shahram
NH=> I am not sure you are capturing all the issues here Shahram.  Some P
LSRs do load-balancing based on IP address hashing as a sort of TE function
because LDP just gives SPF and so leads to networks that are
traffic/topology sensitive.  This gives rise to the additional points:
-	might this not also be considered a security issue itself from a
customer perspective, ie VPN customer IP pkts are looked at for sorting into
different streams?
-	what about the added processing load this creates on the P routers
involved?
-	does it not break the simple 'label forwarding' paradigm that seems
to be the raison detre for MPLS?
-	and don't we effectively get back to IP fowarding now.....albeit
with an inability to do IP forwarding because the P routers don't have the
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neil.2.harrison | 1 Jun 2002 01:14
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RE: Basic LDP Question

Vijay,

You wrote Vijay Bollapragada 31 May 2002 19:34
> 
> On Fri, 31 May 2002, Shahram Davari wrote:
> 
> > Vijay,
> 
> > But LDP does not give you the TE ability. So why use LDP?
> 
> Agreed, that LDP does not give the ability to do TE, I only 
> said use MPLS
> in the core, not necassarily LDP :-) but in any case, Here is 
> what 2547
> draft says about using LDP for the top label..
> 
> Section 4.3.2
> 
> "All that matters for the VPN architecture is that some label switched
> path between the router and its BGP next hop exists.  
> However, to ensure
> interoperability  among systems which implement this VPN architecture,
> all such systems must support LDP [MPLS-LDP]."
> 
> Of course, once could use many other mechanisms to get the vpn_labeled
> packet from one edge PE to another edge PE, Interoperability 
> is the key
> here.
NH=> So are you saying the only reason for LDP is because there is a need to
run VPN services composed of (i) multiple vendors and (ii) multiple SPs
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Ajay Simha | 1 Jun 2002 05:15
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Re: Basic LDP Question

On Fri, 31 May 2002 jh <at> lohi.eng.song.fi wrote:

The point is MPLS effectively decouples the forwarding portion from the
routing. This makes MPLS a service enabler. For instance I did not see anyone
mention things like QoS transparency that MPLS can achieve. Sure you can
monkey around with IP to make IP have everything that MPLS has. May be even a
fixed length tag and call it something else :).

Why do it when this extension already exists as an IETF based standards where
folks like us can debate issues and come up with solutions that are acceptable
to most?

-ajay

>:Robert Raszuk writes:
>:
>: > Currently deployed hardware & software.
>:
>:your current router hardware can't do many other things either, like
>:learning mac addresses.  so when you re-spin it, you could also consider
>:adding real support for ip tunneling for those who don't like the
>:complexity of mpls control plane.
>:
>:-- juha
>:

--

--
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Bakshi, Sanjay | 1 Jun 2002 06:48
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MPLS deployment!!!

Hello...
I have couple of questions regarding the mpls deployment:-

1. Are nested MPLS domains commonly deployed?  
   What is the known largest number of nested MPLS domains? 

2. In the MPLS networks installed today what is the 
   typical number of LSPs installed per port? 

thanks,
-sanjay
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Eric Osborne | 2 Jun 2002 17:33
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Re: Basic LDP Question

On Fri, May 31, 2002 at 11:41:35AM -0700, Shahram Davari wrote:
> Vijay,
> 
> I know all this. The question was: 
> 
> "Why use LDP instead of IP?". 
> 
> If you have an answer please provide.

(coming back from vacation)
Another answer that I haven't seen here is the ability to do cell-mode
MPLS with ATM.  That's one of the original MPLS applications, and LDP
certainly helps with that.

eric

> 
> -Shahram
> 
> > -----Original Message-----
> > From: Vijay Bollapragada [mailto:vbollapr <at> cisco.com]
> > Sent: Friday, May 31, 2002 2:34 PM
> > To: Shahram Davari
> > Cc: 'mpls <at> uu.net'; 'ppvpn <at> ppvpn.francetelecom.com'
> > Subject: RE: Basic LDP Question
> > 
> > 
> > On Fri, 31 May 2002, Shahram Davari wrote:
> > 
> > > Vijay,
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Shahram Davari | 3 Jun 2002 00:33

RE: Basic LDP Question

Ajay,

> -----Original Message-----
> From: Ajay Simha [mailto:asimha <at> cisco.com]
> Sent: Friday, May 31, 2002 11:15 PM
> To: jh <at> lohi.eng.song.fi
> Cc: raszuk <at> cisco.com; Shahram Davari; 'Giles Heron'; 'Yakov Rekhter';
> 'mpls <at> uu.net'; 'ppvpn <at> ppvpn.francetelecom.com'
> Subject: Re: Basic LDP Question
> 
> 
> On Fri, 31 May 2002 jh <at> lohi.eng.song.fi wrote:
> 
> The point is MPLS effectively decouples the forwarding 
> portion from the
> routing.

LDP does not decouple routing from forwarding.

-Shahram
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Maarten Vissers | 3 Jun 2002 11:14
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Re: Sonet Ring provisioning

Vishal,

The answer to this issue is layer networking. I.e. the HOVC layer network sees
the MS SPring protected ring as a set of HOVC fabrics and (1, 2 or 3 types of)
interconnecting HOVC links. 
The HOVC fabrics have a restriction; there is no time slot interchange possible
between the two main links. I.e. the link connection in those two links must
have the same number.

The HOVC control plane selects in which type of HOVC link (protected,
unprotected, preemptable) the new connection has to be created, and then routes
this connection through the HOVC fabrics and links.

The MS SPring [BLSR] control function within the ring network elements (if
supported) will have to populate the ring nodes with the appropriate further
information to run the ring, but this is outside the HOVC control plane's view.

>From a HOVC control plane, this is almost a trivial issue... only constraint is
no "time slot interchange" on ring HOVC links.

Regards,

Maarten

Vishal Sharma wrote:
> 
> Sudheer,
> 
> While I agree that representing nodes/domains/rings etc. is an important
> problem, I think there are two issues being mixed below.
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neil.2.harrison | 3 Jun 2002 12:26
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RE: Basic LDP Question

Ajay,  Let me take you back to the point of Shahram's orginal
question.....which in essence, if I have understood it correctly, was 'what
problem/application is LDP solving/addressing that cannot be done either (i)
using IP directly or (ii) ER LSPs?'.....and which must also take a wider
pro/con analysis of the implications of using LDP-LSPs vs ER-LSPs (or IP
directly).

Please also see below.   Regards, Neil

Ajay Simha wrote 01 June 2002 04:15

> The point is MPLS effectively decouples the forwarding 
> portion from the
> routing.
NH=> Well I agree, this is vital and it's what is needed.  And it's
something we in Telco-land have known/used for years, ie decoupling of the
traffic carrying data-plane and its control-plane (both its own data-plane,
where appropriate, and its routing and signalling protocols).  But LDP does
nothing more than instantiate labels per hop that are locked to the IGP.
That is (i) they take the same SPF routes as the IGP would use for IP
fowarding and (ii) the LSPs change as the IGP changes.  I would argue this
is not a required behaviour for applications where LSPs are long-holding
and/or must not be affected by ad hoc routing changes or failures of routing
protocols (eg VPNs).  Further, because LDP is so tightly coupled to the IGP
then one has to introduce 'layer violations' to make it work a bit better,
eg Load-balancing using IP-level hashing......its hard to take seriously
anyone claiming this is MPLS label forwarding when one has to look at the
client/IP level (which it may not always be, ie XoverMPLS) to make
switching/forwarding decisions.
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Giles Heron | 3 Jun 2002 14:46
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RE: Basic LDP Question

On Mon, 2002-06-03 at 10:26, neil.2.harrison <at> bt.com wrote:
> Ajay,  Let me take you back to the point of Shahram's orginal
> question.....which in essence, if I have understood it correctly, was 'what
> problem/application is LDP solving/addressing that cannot be done either (i)
> using IP directly or (ii) ER LSPs?'.....and which must also take a wider
> pro/con analysis of the implications of using LDP-LSPs vs ER-LSPs (or IP
> directly).
> 
> Please also see below.   Regards, Neil
> 
> Ajay Simha wrote 01 June 2002 04:15
>  
> > The point is MPLS effectively decouples the forwarding 
> > portion from the
> > routing.
> NH=> Well I agree, this is vital and it's what is needed.  And it's
> something we in Telco-land have known/used for years, ie decoupling of the
> traffic carrying data-plane and its control-plane (both its own data-plane,
> where appropriate, and its routing and signalling protocols).  But LDP does
> nothing more than instantiate labels per hop that are locked to the IGP.
> That is (i) they take the same SPF routes as the IGP would use for IP
> fowarding and (ii) the LSPs change as the IGP changes.  I would argue this
> is not a required behaviour for applications where LSPs are long-holding
> and/or must not be affected by ad hoc routing changes or failures of routing
> protocols (eg VPNs).  Further, because LDP is so tightly coupled to the IGP
> then one has to introduce 'layer violations' to make it work a bit better,
> eg Load-balancing using IP-level hashing......its hard to take seriously
> anyone claiming this is MPLS label forwarding when one has to look at the
> client/IP level (which it may not always be, ie XoverMPLS) to make
> switching/forwarding decisions.
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jh | 1 Jun 2002 07:56
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Re: Basic LDP Question

Ajay Simha writes:

 > For instance I did
 > not see anyone mention things like QoS transparency that MPLS can
 > achieve. 

diffserv is a much simpler and more scalable way to achieve qos than
mpls.  if you want to use mpls for qoq, you need to start playing atm
style vc came with p-to-p subscriber resource reservations.  and if you
want to really do it properly, like some atm switches from cisco did,
you need to implement per lsp queueing in your routers.  this is 2002
and i don't want to go back to 1995.

 > Sure you can monkey around with IP to make IP have
 > everything that MPLS has. May be even a fixed length tag and call it
 > something else :).

i don't have any reason to start mimicking mpls with ip.

 > Why do it when this extension already exists as an IETF based
 > standards where folks like us can debate issues and come up with
 > solutions that are acceptable to most?

because mpls is another control plane with all the complexity that comes
with it.  check this out:

harjus:/home/ftp/internet-drafts% ls *mpls* | wc
    146     146    5619

-- juha
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