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

Shahram Davari <davari@broadcom.com> Mon, 20 July 2015 16:27 UTC

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From: Shahram Davari <davari@broadcom.com>
To: "stbryant@cisco.com" <stbryant@cisco.com>, "mpls@ietf.org" <mpls@ietf.org>
Thread-Topic: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
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Date: Mon, 20 Jul 2015 16:27:39 +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 Stewart,

This draft actually saves a lot of memory as it requires only very little MPLS entry table and associated processing.
There are only a few Ethernet MAC headers used in MPLS forwarding, typically one MAC per port, but there can be thousands 
Of swapped labels. So it is not a matter of 14 bytes vs 18 bytes.

We have seen this requirement come up from various data enter operators in Segment routing context.

Thanks
Shahram

-----Original Message-----
From: mpls [mailto:mpls-bounces@ietf.org] On Behalf Of Stewart Bryant
Sent: Monday, July 20, 2015 8:55 AM
To: mpls@ietf.org
Subject: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?


I am curious about how much is actually saved with the MPLS dataplane
change proposed in this draft.

If this is used in an Ethernet environment the LSR already needs to
remove and replace the Ethernet header.

In many implementations the datalink header and the MPLS outer
label are part of the same re-write string. So what is the true
gain in writing 14 bytes instead of 18 bytes?

... or is this planned for use with some pt-pt data link other
than Ethernet which is required to be constant end to end?

- Stewart


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