Subject: last call on hierarchy

From: [email-masked]
Date: Wed, 16 Jan 2002 12:33:46 +0100

Hi,

I would like to clarify two questions regarding the hierarchy draft that is
currently on last call:

1. Dynamic recomputation of the path of the FA-LSP

If I understand correctly, the path information regarding the FA-LSP is
made available to other nodes by means of the PATH TLV. This information
may be used by other nodes for their own path computations. They could for
instance take it into account when computing a backup path. Then if the
FA-LSP changes path, primary and backup path of the client LSPs may no
longer be disjoint.

My proposal would be to foresee the possibility to restrict the
reroutability of the FA-LSP and advertise this in the PATH-TLV. In this
way, nodes that use this information would know whether it is subject to
change or not.

2. Automatic setup of FA-LSP

The draft says "Otherwise (if no existing FA-LSP is found), the LSR sets up
a new FA-LSP.  That is, it initiates a new LSP setup just for the FA-LSP."
I would like to clarify what happens when two FA-LSPs exist that, when
concatenated, can replace the new FA-LSP that is proposed to be set up in
the quoted text.

I would propose to say that the LSR may set up a new FA-LSP or
alternatively, it may replace the hop by a sequence of hops for which FAs
are available.

Would this make sense?

Sven.

---

From: Yakov Rekhter <[email-masked]>
Date: Thu, 17 Jan 2002 10:57:49 -0800

Sven,

> made available to other nodes by means of the PATH TLV. 

Correct.

> This information may be used by other nodes for their own path computations. 

Correct.

> They could for instance take it into account when computing a backup path. 

Correct.

> Then if the FA-LSP changes path, primary and backup path of the client 
> LSPs may no longer be disjoint.

Correct.

> way, nodes that use this information would know whether it is subject to

There may be (at least) two reasons why the FA-LSP gets re-routed:

(1) the current path taken by FA-LSP becomes unfeasible (e.g., one
of the links along the path went down)

(2) there is a "better" path, so FA-LSP is re-routed as part of
optimization.
  
Do you want to restrict re-routability in both cases ? Or only
in the second one ?

> alternatively, it may replace the hop by a sequence of hops for which FAs

that would be ok, *provided* that the the strict hop subsequence 
from the ERO carried by the new LSP matches the one resulted from
the concatenation of several FA-LSPs. Agreed ? 

Yakov.