Re: [mpls-tp] Demultiplexing to BFD sessions

[Mukund Mani <[e-mail]>]

Hi Apratim

For your first point I agree with you and had raised this some time back. I
was under the impressions that things would be clear with the next version
of the CC/CV draft.
But I would like to mention here w.r.t the scenario of independent sessions.
As per CC/CV draft, Your Discriminator will be zero when not known else it
can reflect the
My Discriminator vlaue.
So the fast packets for BFD1 from Node A to Node B, can have both both the
Your and My discriminators present. So when I say that label alone
is not enough to demultiplex, that is because (as you mention) both the fast
and slow packets would arrive with the same label. Thus we
anyway need to refer to the Your discriminator value also to find the
correct session context . So in case of independent sessions label and
discriminator might both be required
to find the session context.

For the MEP id, IMHO even for the independent session case, considering
associated bi-directional LSP,
we would have a Source and a Sink MEP for each direction. The BFD session
initiator of each independent session (at either end) will be identified IMO
as mentioned below in
my previous mail..


With Regards
Mukund

On Thu, Jul 1, 2010 at 12:52 PM, Apratim Mukherjee
<[e-mail]>wrote;wrote:

>  Hi Mukund /Shahram
>
>
>
> I think single BFD bidirectional session and unique MEP Ids are all correct
> arguments for the normal use-case.
>
>
>
> I have attempted to raise the point only in context  of *‘independent’*BFD sessions over a bidirectional LSP ( for 1+1 uni-directional switchover
> case).
>
> In this case , my understanding is that there are 2 BFD sessions running independent of
>
>

>  each other with each BFD session protecting one direction of the LSP. ( Section 3.5 of draft-ietf-mpls-tp-cc-cv-rdi-00 : “A single bi-directional BFD session is used for fate sharing operation. Two independent BFD sessions are used for independent operation.”
>
>
>
> Node A
>                               Node B
>
> OutLabel = L11 à BFD1 fast packets   + BFD2 packets during state change à
> InLabel = L11
>
> InLabel  = L12 ß BFD1 packets during state change + BFD2 fast packets   à     OutLabel
> = L12
>
>
>
> So if L11 side is down , in steady state BFD1 is in Down State on Node B
> but BFD2 is in Up State on Node B .
>
>
>
> In steady state my assumption is that Discriminators will be different from
> same node for the two sessions.
>
>
>
> My assumption here is that when Node B is sending BFD1 and BFD2 packets
> both using OutLabel = L12 AND if Your Discriminator is 0 in the packet,
>
> Node A has no way to distinguish between packets for BFD1 or BFD2 . The
> only difference is really the Min Rx Interval in the packets .
>
> I assumed here that  even if MEP Id is included , the MEP Id as defined
> today would be Global Id + Node B Id + TunnelId + Lsp id in both the packets
> I.e for Node B Rx and Tx links have the same Lsp Id  unless I have got the
> definition for MEP Id wrong.
>
>
>
> P.S : I think I am missing something here regarding the MEP IDs from Greg’s
> mail snippet
>
> Per Greg “I think "independent" OAM uni-directional OAM session requires
> separate MEG and, consequently, MEP ID will be unique for each session,
> direction of the bi-directional LSP in your scenario. That is why I think
> that MEP ID TLV would not be the same as you've suggested.”
>
>
>
> Per Mukund “IMHO the MEP id will be different.  Eg as far as the
> identification goes say the forward direction is from node A to node B, MEP
> for the forward path can be identified as A::Tnl X::LSP1 and the reverse
> path MEP can be identified as B::Tnl Y::LSP2.” à I think this is for
> bi-directional sessions but not true for the independent mode we are
> discussing here .
>
>
>
>
>
>
>
> Regards,
>
> Apratim
>
>