Re: [trill] FGL "safe" mode in fine labels

"Matt Anger (manger)" <> Wed, 20 March 2013 21:34 UTC

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From: "Matt Anger (manger)" <>
To: Thomas Narten <>, Radia Perlman <>
Thread-Topic: [trill] FGL "safe" mode in fine labels
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Date: Wed, 20 Mar 2013 21:34:16 +0000
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Subject: Re: [trill] FGL "safe" mode in fine labels
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That is not what the spec as I interpret it says.

In 2) you can have FGL frames, but they are only allowed to be sent across
switches that are FGL-safe.
Meaning if you don't have a complete route A<->B where all the in-between
switches are FGL-safe, then the frame can NOT be transmitted as FGL.

  /  \  /  \
A<    ><    >B
  \  /  \  /

In this example you need one of (S1 and S2) and one of (S3 and S4) to be
FGL-safe for FGL frames to be able to go from A<->B

So if S1 and S3 are FGL-safe and S2 and S4 are NOT FGL-safe, then the link
costs *must* be calculated such that FGL frames always go A->S1->S3->B
(and never over S2 and S4 which are NOT FGL-safe) and FGL is ok to be


On 3/20/13 4:19 PM, "Thomas Narten" <> wrote:

>> No!  There isn't any mention in the document of "operating in VL
>> mode", whatever it is you might mean by that.
>Operating in "VL mode" (to me) means you don't know anything about FGL
>and operate as described in RFC 6325 et al. I.e., the base mode of
>operation for TRILL. I think it's useful to define a term like "VL
>mode" to describe that behavior to distinguish it from RBs that have
>somehow enabled and are using FGL.
>> If R1 is FGL-safe, and if R1's neighbor R2 does not claim to be
>> then R1 does not forward FGL frames to R2.  R1 does not do anything
>> different if some non-neighbor of R1, say R3, is not FGL-safe.
>The above says to me that you now have a TRILL campus where R1 does
>process FGL frames and R2 does not. But doesn't that contradict the
>> 1) VL-only (today's deployment), then
>> 2) A mixture of VL and FGL-safe, until
>> 3) EVERYone upgraded to FGL-safe, then
>> 4) FGL-links can be introduced.
>Or maybe we are having a violent agreement? if we are at step 2)
>above, then isn't the entire campus operating in "VL mode"? I.e., at
>step 2, no one is sending/receiving/processing FGL frames. (Right?)
>It's not until step 3/4 that you see *any* FGL frames being used. And
>for that, you can't have *any* RBs still operating only in VL mode -
>they *all* have to support FGL.
>What is it that I'm not understanding?
>trill mailing list