Subject: Requirement for LDP support in the RFC2547bis draft

From: "Sasha Vainshtein" <[email-masked]>
Date: Tue, 9 Jan 2001 12:52:43 +0200

Dear Mr. Rosen,
  I an relatively new to the discussions in the MPLS WG, and I would highly
appreciate some explanation on the following subject:
    The original RFC2547 does not mention LDP at all.
    However, its proposed update, draft-rosen-rfc2547bis-02.txt, refers to
LDP in two places:
      a.. In section 4.3.2. "Route Distribution Among PEs by BGP", it
states:<quote> Note that the use of BGP-distributed MPLS labels is only
possible if there is a label switched path between the PE router that
installs the BGP-distributed route and PE router which is the BGP next hop
of that route... <skip> All that matters for the VPN architecture is that
some label switched path between the router and its BGP next hop exists.
However, to ensure interoperability among systems which implement this VPN
architecture, all such systems must support LDP <end quote>
      b.. In section 5, "Forwarding Across the Backbone", it states: <quote>
To ensure interoperability among different implementations, it is required
to support LDP for setting up the label switched paths across the backbone.
However, other methods of setting up these label switched paths are also
possible <end quote>.
    I assume that in both cases the LSPs in question are the paths for the
outer (i.e., PE-to-PE) level encapsulation, and that requirement for LDP
support states from the fact that such a support would gurantee ability to
create such an  LSP, e.g., by requesting a label for the egress PE IP
address (known to the ingress PE as the BGP next hop) in a standard way. Is
this assumption correct? If this is the case, do the two quotations actually
refer to the same problem and its solution?
    I would also like to understand the subtle difference between the (lower
case) "must" in the quoted sections of draft-rosen-rfc2547bis-02.txt and the
(capitalized keyword) MUST described in RFC2119.
______________________________________________
With best regards,
Sasha Vainshtein
mailto: [email-masked]
phone: +972-3-7659993 (office)
fax:      +972-3-6487779 (office)

---

From: "Yoav Levy" <[email-masked]>
Date: Wed, 10 Jan 2001 09:15:08 +0200

It was really surprising to see such constrain without any good reason. It’s
like forcing the usage of isis (or ospf) in the BGP RFC …

Yoav Levy

Charlotte's Web Networks Ltd.

http://www.cwnt.com
Email: [email-masked]
Tel: +972-4-9592203  ext. 242
Fax: +972-4-9593325
2 Hamada St, P.O.B 303, Yokneam 20600, ISRAEL

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Sasha
Vainshtein
Sent: Tuesday, January 09, 2001 12:53 PM
To: [email-masked]
Cc: Alik; [email-masked]
Subject: Requirement for LDP support in the RFC2547bis draft

Dear Mr. Rosen,
I an relatively new to the discussions in the MPLS WG, and I would highly
appreciate some explanation on the following subject:
The original RFC2547 does not mention LDP at all.
However, its proposed update, draft-rosen-rfc2547bis-02.txt, refers to LDP
in two places:
*      In section 4.3.2. "Route Distribution Among PEs by BGP", it
states:<quote> Note that the use of BGP-distributed MPLS labels is only
possible if there is a label switched path between the PE router that
installs the BGP-distributed route and PE router which is the BGP next hop
of that route... <skip> All that matters for the VPN architecture is that
some label switched path between the router and its BGP next hop exists.
However, to ensure interoperability among systems which implement this VPN
architecture, all such systems must support LDP <end quote>
*      In section 5, "Forwarding Across the Backbone", it states: <quote> To
ensure interoperability among different implementations, it is required to
support LDP for setting up the label switched paths across the backbone.
However, other methods of setting up these label switched paths are also
possible <end quote>.
I assume that in both cases the LSPs in question are the paths for the outer
(i.e., PE-to-PE) level encapsulation, and that requirement for LDP support
states from the fact that such a support would gurantee ability to create
such an LSP, e.g., by requesting a label for the egress PE IP address (known
to the ingress PE as the BGP next hop) in a standard way. Is this assumption
correct? If this is the case, do the two quotations actually refer to the
same problem and its solution?
I would also like to understand the subtle difference between the (lower
case) "must" in the quoted sections of draft-rosen-rfc2547bis-02.txt and the
(capitalized keyword) MUST described in RFC2119.
______________________________________________
With best regards,
Sasha Vainshtein
mailto: [email-masked] <mailto:[email-masked]>
phone: +972-3-7659993 (office)
fax:      +972-3-6487779 (office)

---

From: Eric Rosen <[email-masked]>
Date: Wed, 10 Jan 2001 11:26:10 -0500

Sasha> I assume  that in both cases the  LSPs in question are  the paths for
Sasha> the outer (i.e., PE-to-PE)  level encapsulation, and that requirement
Sasha> for  LDP support  states  from the  fact  that such  a support  would
Sasha> gurantee ability to  create such an LSP, e.g.,  by requesting a label
Sasha> for the egress PE IP address (known to the ingress PE as the BGP next
Sasha> hop) in  a standard way. Is  this assumption correct? If  this is the
Sasha> case, do  the two quotations actually  refer to the  same problem and
Sasha> its solution?

Yes.  The requirement for LDP support  is there to ensure that two compliant
implementations can interoperate.  There is no requirement that LDP actually
be used, if some other method is available.

Sasha> I would  also like  to understand the  subtle difference  between the
Sasha> (lower case) "must" in the quoted sections of draft-rosen-rfc2547bis-
Sasha> 02.txt and the (capitalized keyword) MUST described in RFC2119.

I  don't think  there is  any difference  between "must"  and "MUST"  in the
section you quoted.