The MPLS WG Archive

["Peter Ashwood-Smith" <petera@nortelnetworks.com>]

Title: RE: [mpls] mpls vs IPv6

  You are correct that many of the original motivations for MPLS are no longer really valid.
Forwarding speed as you point out is less relevant; Encapsulation can be done other ways such that MPLS would only be required at the service level;

  The one thing that you cannot easily do without label substitution forwarding is non shortest path forwarding. If you ever want a subset of your traffic to diverge from the routes IP would give, you either have to:

   A) use source routing (stateless).
   B) use label substitution (statefull).
   C) Create multiple instances of another hop-by-hop protocol i.e multiple forwarding tables and a way to figure out which one to use, i.e. DHCP/flow etc. could key which table ..

  This is of course true regardless of the address size or how QOS is implemented per hop. Right now B) seems the most practical option although with bandwidth getting cheaper by the nanosecond it can't be long before new forms of A) arrive.

  Peter

-----Original Message-----
From: mpls-bounces@lists.ietf.org [mailto:mpls-bounces@lists.ietf.org]
Sent: Tuesday, October 12, 2004 4:26 AM
To: Marc Binderberger; Jung Janos
Cc: mpls@ietf.org
Subject: Re: [mpls] mpls vs IPv6

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

some more queries inline.>

--- Marc Binderberger <marc@sniff.de> wrote:

> 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.
>

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

> 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.
>

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

> > 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 ;-)
>

> Same as for IPv4: TE capabilities, allows you to
> integrate ATM into
> your IP packet network, [...].
>
But why woould I need ATM then?

               
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