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[mpls] Re: [MPLS-OPS]: label space configuration

  • From: shilpa goel <shilpa07@gmail.com>
  • Date: Tue, 12 Dec 2006 09:33:03 +0530
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Hi,

 Thanks for the clarification. I still have 2 doubts in this.

Firstly, what is meant by the line  'as the router knows about all of them'?  (2nd para)

Also, this is clear that for ATM, interface label space should be used but why should platform wide labelling be used in an Ethernet configuration i.e. why can't we use interface label space for ethernet also thereby seeking the same advantage as we are getting for ATM?

thanks,
Shilpa

On 12/4/06, Roger Williams (rogwilli) <rogwilli@cisco.com> wrote:
Shilpa, platform-wide labeling is used in an Ethernet configuration, whereas port or interface lablespace is used for ATM.
 
Basically what that means is that for Ethernet a given router advertises its whole self with one label upstream. All ports would be covered under that single label advertisement, as the router knows about all of them. And it is done as soon as the underlying IGP routing protocol knows there are routes to be labeled, not waiting for the demands of traffic to build label paths.
 
With ATM the doling out of labels is much more conservative, and done only when requested by traffic demand. The reason for this is the limited number of VCs that an ATM switch can support (I think 4096). The labels point to a VC underneath it all. Since there is no routing done at the Layer 2 of an ATM switch, each label is used as a per-interface advertisement, which effectively is a per-VC advertisement.
 
I hope that helps.
 
Roger.

From: shilpa goel [mailto:shilpa07@gmail.com]
Sent: Monday, December 04, 2006 12:24 AM
To: mpls@uu.net; mpls-ops@mplsrc.com; mpls@lists.ietf.org
Subject: [MPLS-OPS]: label space configuration

Hi..

  Can you please give me an insight as to how label space (per interface or per platform) is configured in a LSR i.e. what all considerations need to be taken into account:

for 2 cases-
    -LSR consisting of only ethernet ports
    -LSR consisting of both ATM and ethernet interfaces

thanks and regards,
Shilpa

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