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Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?

Shahram Davari <davari@broadcom.com> Thu, 23 July 2015 21:07 UTC

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From: Shahram Davari <davari@broadcom.com>
To: Robert Raszuk <robert@raszuk.net>, Eric C Rosen <erosen@juniper.net>
Thread-Topic: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
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Date: Thu, 23 Jul 2015 21:07:26 +0000
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Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
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Hi Robert,

How are these labels distributed? Via LDP or via SDN controller?

Thanks
Shahram

From: rraszuk@gmail.com [mailto:rraszuk@gmail.com] On Behalf Of Robert Raszuk
Sent: Thursday, July 23, 2015 12:58 PM
To: Eric C Rosen
Cc: Shahram Davari; stbryant@cisco.com; mpls@ietf.org
Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?

​Hi Eric,​

​​
If you notice that the incoming label needs to be 'replaced' by an outgoing label of the same value, you could just make the rewrite string shorter, so it won't overwrite the top label on the stack.  This seems to be what the draft suggests, but it could be done as an optimization for the particular case where the incoming and outgoing labels have the same value.

​This is precisely ​the crux where your statement fails.

You use term "incoming label" and "outgoing lable" ... well in the new architectures there is no such things.

It is a "global label" or "path label" with adjacency information.

So to support legacy hardware new control plane has to make up from single label now two (identical) labels to pass it to data plane. Now also data plane must be smart to check that and program its state per your suggestion.

Why would we do that other then due to worry about legacy chipsets feared to be non compliant to new RFC ?

Many thx,
R.

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