Re: [trill] Explaining three options for upgrading to FGL (fine-grained-labeling)

Ayan Banerjee <ayabaner@gmail.com> Tue, 29 January 2013 19:45 UTC

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Date: Tue, 29 Jan 2013 11:45:02 -0800
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From: Ayan Banerjee <ayabaner@gmail.com>
To: Anoop Ghanwani <anoop@alumni.duke.edu>
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Cc: Radia Perlman <radiaperlman@gmail.com>, "trill@ietf.org" <trill@ietf.org>
Subject: Re: [trill] Explaining three options for upgrading to FGL (fine-grained-labeling)
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I agree with Anoop here.

I think that we are describing a network that is FGL-safe and ready and
then switch to FGL-mode. However, we need some statements to account for a
VL-node coming-in/leaving-the network due to a flaky link.

Thanks,
Ayan



On Tue, Jan 29, 2013 at 6:42 AM, Anoop Ghanwani <anoop@alumni.duke.edu>wrote:

> At noted, option 1 looks dangerous so that should be ruled out.
>
> Option 2 seems reasonable.  It might be useful to clarify a couple of
> things:
> - Can the FGL-safe campus have both VLAN & FGL frames going around?
> - Do all RBridges need to agree on when the campus is FGL-safe?  I would
>   hope not.  But the problem I'm thinking about is where RB1 thinks
> the campus is
>   FGL-safe and starts announcing attachment to FGL links, but RB2 hadn't
> yet
>   concluded that process and it see RB3 which happens to be VL.
>
> Option 3 seems to introduce more complexity to solve this problem than
> is necessary.
>
> Anoop
>
> On Fri, Jan 25, 2013 at 11:00 AM, Radia Perlman <radiaperlman@gmail.com>
> wrote:
> > I'm going to summarize three options for phasing-in FGL, and explain the
> > tradeoffs, to help people have informed opinions about the implications
> of
> > the three approaches.  There are infinite variations, of course, but as I
> > said, I'll describe three main ones.
> >
> > Option 1:  Original draft, no changes.  There are two types of RBridges.
> The
> > first type is "VL" which only understands VLAN tags, and have unknown and
> > possibly dangerous behavior when they receive an FGL-labeled packet.
> (e.g.,
> > decapsulate a packet onto a link where it is not allowed, or mistakenly
> > prune a multicast so it does not reach everywhere it should). The second
> > type is "FGL".  FGL guys need to do two things: 1) understand FGL tags
> and
> > do the right thing with them, and 2) ostrasize VL guys...meaning that an
> FGL
> > guy refuses to form an adjacency with a VL guy.  This option is very
> simple
> > for implementers of FGL, but the implication is that you have to upgrade
> > your entire campus to FGL at once.  There is no coexistence.
> >
> > Option 2: Two types of RBridges, but the 2nd type is different from
> option
> > 1.  VL guys of course are the same as in option 1...they cannot be
> trusted
> > with FGL frames. The second type I will call "FGL-safe". An FGL-safe
> RBridge
> > must advertise in its LSP that it is FGL-safe, and it must not "do
> anything
> > bad" with FGL frames, meaning that it is allowed to ignore pruning of FGL
> > (or even VL frames) entirely...it just can't falsely drop FGL frames.
>  And
> > it must not decapsulate an FGL frame onto a link for which that FGL frame
> > doesn't belong. In this option, all RBridges must be upgraded to
> FGL-safe,
> > but it need not happen instantaneously...it's fine to mix FGL-safe
> RBridges
> > with VL RBridges...it's just not safe to inject FGL frames yet.  Once all
> > the RBridges have been upgraded to be FGL-safe, then edge RBridges can
> start
> > announcing they are connected to an FGL link, and can start injecting FGL
> > packets.  It is considered a misconfiguration if you start injecting FGL
> > frames before all the RBridges are upgraded to FGL-safe, so an additional
> > chore for an FGL-safe RBridge R1 is to examine LSPs, and if any RBridge
> > claims to be attached to an FGL link, then R1 must ostrasize any VL
> > neighbors.  (don't start ostrasizing VL guys until it is necessary
> because
> > of actually starting to use FGL frames, in other words). This option is
> more
> > work for the upgraded RBridges than option 1, and there still isn't good
> > coexistence with VL guys long-term (as option 3 will), but it does allow
> > upgrading RBridges one by one in a working campus without causing
> > disruption.
> >
> > Option 3: Two types of RBridges.  VL, of course, is the same as in
> options 1
> > and 2.  This option makes FGL guys do more work, but allows maximal long
> > term coexistence of VL and FGL guys. In this option, FGL guys calculate
> > unicast paths to FGL edge guys that avoid any VL guys, and calculate at
> > least one FGL-friendly multicast tree that also avoids any VL guys. So
> let's
> > say R1 is an FGL guy.  R1 discards all LSPs from VL guys (ones that don't
> > advertise FGL capability in their LSP), when calculating paths to other
> FGL
> > RBridges. Then R1 calculates paths to the VL guys using all LSPs.
>  Likewise,
> > when calculating an FGL-friendly tree, R1 calculates a tree through only
> FGL
> > guys.   This option is more work for the upgraded RBridges (because they
> > have to calculate Dijkstra in two different ways, one for reaching VL
> guys,
> > and one for reaching FGL guys).  However, it does allow having long-term
> > coexistence with VL guys.  For instance, you could forever keep some VL
> edge
> > RBridges that communicate just fine through an FGL core.  They can stay
> > there forever, and still be able to communicate through the core to all
> the
> > links attaching to their VLAN.
> >
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> >
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