The MPLS WG Archive

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

Giles,

> -----Original Message-----
> From: Giles Heron [mailto:giles@packetexchange.net]
> Sent: Friday, May 31, 2002 2:48 PM
> To: Shahram Davari
> Cc: 'mpls@uu.net'; 'ppvpn@ppvpn.francetelecom.com'
> Subject: RE: Basic LDP Question
> 
> 
> On Fri, 2002-05-31 at 17:41, Shahram Davari wrote:
> > Giles,
> > 
> > > -----Original Message-----
> > > From: Giles Heron [mailto:giles@packetexchange.net]
> > > Sent: Friday, May 31, 2002 2:37 PM
> > > To: Shahram Davari
> > > Cc: 'mpls@uu.net'; 'ppvpn@ppvpn.francetelecom.com'
> > > Subject: Re: Basic LDP Question
> > > 
> > > 
> > > 1.  Efficient encapsulation of VPN traffic
> > 
> > Do you mean the difference between 4 bytes label and 20 
> bytes IP header?
> 
> yes.

Although you save 16 bytes per packet (~ 3% BW saving, assuming ~500 bytes average IP packet size), but you create another problem:

MPLS is much more prune to failure than IP. If an LSR's MPLS switching table is
corrupted, the packet ends up in wrong PE, while if a router's IP routing table
is corrupted, the next hops could sent the packet to the right destination PE.


> 
> > > 2.  Ability to run VPN on current hardware
> > 
> > But current hardware have IP already, it is much easier to run
> > IP rather than LDP MPLS. isn't it?
> 
> don't think so.  I believe many current routers with MPLS support can
> push multiple labels when sending a packet, but can't "push" 
> an extra IP
> header?

May be, but when LDP was created there was no box doing VPN. 

-Shahram

> 
> Giles
>  
> > -Shahram
> > 
> > > 
> > > There are probably other reasons as well...
> > > 
> > > On Fri, 2002-05-31 at 17:28, Shahram Davari wrote:
> > > > Hi,
> > > > 
> > > > What problem a mp2p LDP-based MPLS network is trying to 
> > > solve (like the one used in RFC2547) that can't be done with 
> > > pure IP forwarding?
> > > > 
> > > > Note: Don't tell me fast forwarding, because we can do fast 
> > > IP lookup as well.
> > > > 
> > > > Yours,
> > > > Shahram
> > > > 
> > > > 
> > > -- 
> > > =================================================================
> > > 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"
> =================================================================
>