Subject: RE: [Forces-protocol] topic 2:: HA

From: "Khosravi, Hormuzd M" <[email-masked]>
Date: Mon, 26 Apr 2004 14:03:58 -0700

Hi Jamal,

Thanks for your comments. I mostly agree with them. See more comments
below...

-----Original Message-----
From: Jamal Hadi Salim [mailto:[email-masked]] 
> 
> Based on our discussions on TML and PL as well as the 3 schemes
proposed
> by Jamal, here is my suggestion for HA scheme...
> 
> At any time there is one Primary CE controlling the FE and there can
be
> multiple secondary Ces. The FE PL is aware of the primary and
secondary
> Ces. Only the primary CE is sending Control messages to the Fes. The
FE
> may choose to send its events, redirection packets to all the Ces or
> only Primary CE (we need to decide one or keep this configurable ?). A
> CE-to-CE synchronization may be needed, however that is out of our
> current scope for ForCES PL. The association between the FE and
primary
> CE may change based on the Connection State (triggered by TML) or an
> explicit message (such as Move, described by Jamal) from the primary
CE.
> 
> This scheme is similar to Scheme 2 proposed by Jamal with a few more
> details. Hope we can agree on this and move to the other topics. We
can
> discuss more details around the Protocol Messages related to this
scheme
> during topic:4. 

There is a difference in that in my text i said the responsibility is
that of the TML - not the PL. The only role the PL may play is in the
move operation. That role could also be played by the FEM/CEM interface
making the decision making out of the control of the PL.

So i think actually your email adds some clarity to what i had said
earlier since you are thinking from a PL level and i was fromn the TML
level ;->
I see both as valuable and of different responsibilities:

1) TML level - Transport level:

a) The TML controls logical connection availability and failover. 
b) The TML also controls peer HA managements.

At this level in my opinion control of all lower layers
example transport level (such as IP addresses, MAC addresses etc)
and associated links going down are the role of the TML or whatever the
TML depends on.

[HK] Agreed

2) PL Level:
If  you are talking about control of say CEids as the meaning of "FE
being aware of the primary and secondary Ces", then i think it would be
sensible. When i read the text it almost sounded like the PL layer knew
about details of things like physical links going up/down.
 
To put the two together, for example if a path to a master CE is down,
I would think the TML would take care of failing over to a backup path.
Should the CE be totaly unreachable i think only then would the PL
be informed and it may decide to move to a new CE.
Does this make sense?

[HK] Yes, this was my thinking as well. Thanks for adding more text and
clarity! I'll send out a more detailed text summarizing the points made
by yourself, Weiming, Ram et al.

BTW, just wanted to clarify what you meant by 'backup path' above? I am
guessing that some TML might implement multiple paths, e.g. multiple
TCP/UDP connections between CE & FE. Is that what you mean ? 

regards
Hormuzd

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---

From: Jamal Hadi Salim <[email-masked]>
Date: 26 Apr 2004 17:41:00 -0400

> TCP/UDP connections between CE & FE. Is that what you mean ? 

Multiple TCP/UDP connections could be one of the modes that the TML is
responsible for. It could also be multihomed, multinexthop reachable,
trunked in active/backup mode, ethernet bonded etc. Point is it is a
blackbox and the PL doesnt care about those details.
 
To provide an example:
Consider CE with id #102 which is currently considered master.
Consider that at the low layer is infact reachable as IP address a.b.c.d
and IP address z.x.y.v etc. 
Consider CE with id #103 and ip address w.e.r.t reachable via interface
3 with nexthop of s.d.f.g and a.w.d.r.
The Forces ids #102 and #103 is what PL cares about. The IP addresses is
what the TML cares about.
At some point when the TML has no way of reaching #102 via any of its
know addresses, then the PL needs to make a call to move to CE #103

cheers,
jamal