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

Eric C Rosen <erosen@juniper.net> Mon, 20 July 2015 18:44 UTC

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To: Shahram Davari <davari@broadcom.com>, "stbryant@cisco.com" <stbryant@cisco.com>, "mpls@ietf.org" <mpls@ietf.org>
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Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
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On 7/20/2015 2:07 PM, Shahram Davari wrote:
> The new swapped labels (The outgoing  label that replaces the
> incoming label) need to be stored in a table. Using this draft
> reduces the number of swapped labels that needs to be stored,
> regardless of  implementation. Don't you agree?

No.  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.  You could do this today, as a local implementation 
optimization. There doesn't seem to be any interop issue or any change 
to the data plane semantics.

> It also reduces the configuration and management of the new swapped labels.

We're not discussing whether there are any advantages to the use of 
domain-wide labels.  We're discussing whether the use of domain-wide 
labels requires a change in the forwarding plane architecture.  I just 
don't see that it does.