Subject: Re: [mpls] mpls vs IPv6

From: Marc Binderberger <[email-masked]>
Date: Sun, 10 Oct 2004 12:08:33 +0200

Hello,

> With MPLS I can create MPLS VPNs, QoS can (really?) be
> granted to packet flows, and routing is more faster.

Forget about the "faster". Today the forwarding happens either in 
hardware and is wire-speed for IPv4/IPv6 as well. Or it's the same 
underlying mechanism in software, e.g. the "CEF" table in Cisco 
routers.

QoS for MPLS is in first place the same as for IPv4/IPv6. You have 3 
bits, like the (old) IPv4 Precedence. In theory more QoS information 
could be coded in the label, of course.

> IPv6 has the "Flow label" field wich makes routing faster

again, the "faster" doesn't matter with today's ASICs in place.

> and has less header overhead than ipv4 (or mpls+ipv4)

n*4+20 vs. 40 - less overhead?

> And i think flow label could have the same use as
> the mpls label value...
>
> How is MPLS to IPv6 related?

as already answered: the same as MPLS to IPv4.
Well, there is always a difference between theory and implementation. 
MPLS needs LDP (and RSVP depending on what you do), LDP uses IP UDP and 
TCP. Although informations within are "TLV" coded and thus expandable I 
haven't seen any IPv6-based LDP on my Cisco so far. Read: you may have 
IPv4 to run protocols like LDP to finally run MPLS carrying IPv6 
packets.

> Are they technologies that have nothing to do with each other?

 From a generic point of view: correct.

> Or MPLS can bring new functionalities to IPv6 networks (like to IPv4), 
> and
> so mpls+ipv6 would have a sense?

exactly. Hope I don't start a religious war now but look upon IPv6 as 
an IPv4 with larger addresses, a more structured approach to "ip 
options", avoiding fragmentation (on transit routers) and such. In 
short: more addresses ;-)

> And if so, what are the benefits?

Same as for IPv4: TE capabilities, allows you to integrate ATM into 
your IP packet network, [...].

> IPv6 has all what mpls+ipv4 has (separeted flows to support qos
> VPNs faster routing) and so mpls would have no further use?

Don't see that IPv6 has any VPN support (other than IPSec which IPv4 
supports as well).

Regards, Marc
--
Marc Binderberger    <[email-masked]>    Powered by *BSD ;-)

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From: Spice Sylvia <[email-masked]>
Date: Tue, 12 Oct 2004 09:26:12 +0100 (BST)

May I be bold enough to ask the reason MPLS was ever
deployed?

some more queries inline.>

> underlying mechanism in software, e.g. the "CEF"

And how many such end addresses are there? Do we need
to throw out the existing gear to move to IPv6?

> again, the "faster" doesn't matter with today's

But then tomorrow's ASICs will be faster than today's
so why not wait for tomorrow :)) till they are built
??

> your IP packet network, [...].
But why woould I need ATM then?

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From: Marc Binderberger <[email-masked]>
Date: Tue, 12 Oct 2004 12:07:53 +0200

Hi Sylvia,

> May I be bold enough to ask the reason MPLS was ever

good marketing opportunity? ;-)

Serious: there are probably some folks on the list who invented MPLS, 
being able to give you all reasons. Here a few from my limited point of 
view:

* the speed argument: MPLS is now 8 years old (I think. or even 
older?), at that time Silicon to swap labels had been available for ATM 
already while hardware-based routing was still expensive, less mature 
and so on. _Today_ the argument is not valid anymore - but that's 8 
years later.

* Larger ISPs in the US often had an ATM core with routers at the edge 
and any-any PVC meshing. What is called the overlay model. Doesn't 
scale well for your IGP, so making the ATM switches part of your 
IGP/MPLS (the "peer" model) scales better. For invest protection etc. 
you want to use the existing ATM boxes.

Then we had the Internet bubble. Bandwidth for free (well, or not). 
Suddenly you had 10Gbit/s networks out there - and a need to use them.

* Do you wanna build a separate ATM/FR network? No, you want similar 
capabilities on your router network, so you get TE.

* Fast rerouting because these new networks often are DWDM, not SDH 
based anymore (read: unprotected wavelength).

Additionally some bright minds realized how cool the routing protocols 
are in the IP world. Instead of SDH rings - somewhat limited - it would 
be more flexible and even cheaper (hmm) when you run meshed networks. 
So suddenly you have stuff like OSPF on your transmission equipment for 
circuit setup etc ... well, you need more than OSPF and (G)MPLS as the 
generic control plane comes into play here.

As I said: just a few reasons. Many different motivations meanwhile.

> to throw out the existing gear to move to IPv6?

this problem is not related to MPLS, is it? In fact I know hardware 
where MPLS is the only way to run IPv6 at high speed - because the MPLS 
"hides" the IPv6 which some ASICs cannot deal with (and you don't wanna 
run STM16 on a 200MHz MIPS R5000 ;-)

> so why not wait for tomorrow :)) till they are built

faster than wire speed? ;-)

> But why woould I need ATM then?

See above: some _have_ ATM networks and want to integrate IP and ATM 
networks into one.

Regards, Marc

P.S.: is this "historical" discussion Off-Topic for the list? In this 
case I apologize and switch over to private comm channels :-)
--
Marc Binderberger    <[email-masked]>

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From: Spice Sylvia <[email-masked]>
Date: Tue, 12 Oct 2004 13:57:50 +0100 (BST)

Hi Marc/list,

I will take this offline, I just realised it is OT, 
Am sorry to have marked the list and my apologies on
the same.

-brgds
Sylvia.

> being able to give you all reasons. Here a few from

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