Subject: Re: WGLC comments on bfd-mpls-05

From: Carlos Pignataro <[email-masked]>
Date: Mon, 05 May 2008 16:10:50 -0400

Hi Rahul,

Thank you for your answers, please find some follow-ups below.

On 4/30/2008 11:41 PM, Rahul Aggarwal said the following:
> Hi Carlos,
> 
> Thanks for the comments. Please see below:
> 
>> Please find a couple of comments regarding bfd-mpls-05. I realize this
>> is way past end of WGLC, but I hope the comments are useful and can be
>> given consideration.
>>
>>
>> 3.1. BFD for MPLS LSPs: Motivation
>>
>>        The LSP may be  associated with any of the following FECs:
>>          a) RSVP IPv4/IPv6 Session [RFC3209]
>>          b) LDP IPv4/IPv6 prefix [RFC3036]
>>          c) VPN IPv4/IPv6 prefix [RFC4364]
>>          d) Layer 2 VPN [L2-VPN]
>>          e) Layer 2 Circuit ID [RFC4447]
>>
>> Does item e) refer to both the PWid FEC and the Generalized PWid FEC
>> (128 and 129)?
>>
> 
> Yes. I will clarify this.
> 
>> Are BGP Labeled IPv4/IPv6 prefixes [RFC3107] excluded for a reason?
>>
> 
> Will add BGP labeled prefixes to the list.
> 
>> Also, for the e) FECs, there is the VCCV signaling aspects to be
>> considered, from RFC4447 / RFC5085 to provide the VCCV control channel
>> associated with the PW before BFD could be sent. Please also see last
>> comment.
>>
> 
> More on this below.

Thanks, please see below as well.

> 
>> ---
>>
>> 3.2. Using BFD in Conjunction with LSP-Ping
>>
>>         a) Association of a LSP-Ping echo request message with a FEC. In
>>       the case of Penultimate Hop Popping (PHP), for a single label stack
>>       LSP, the only way to associate a fault detection message with a FEC
>>       is by carrying the FEC in the message.
>>
>> Is this the case not only for PHP but also for UHP with exp-null?
> 
> Correct. Will clarify this.
> 
>> Additionally for aggregated FECs in general (e.g., in the case of
>> per-VRF label vs. per-VPNv4-FEC label, etc) the same applies but OTOH
>> there would need to be only one BFD session per "vrf aggregated fec"
>> (since it's the same label stack for different VPNv4 FECs, and the LSP
>> being tested is identical), correct? Could this be clarified in the
>> document?
>>
> 
> The spec is clear on this subject in section 4:
> 
> "If the LSP
>    is associated with multiple FECs, a BFD session SHOULD established
>    for each FEC. For instance this may happen in the case of next-hop
>    label allocation. Hence the operation is conceptually similar to the
>    data plane fault detection procedures of LSP-Ping."
> 
> 

OK, Thanks, that's clear (sorry I missed it when reading the previous 
part). And implicit-ack on the responses I skip over.

> 
>>       LSP-Ping provides this
>>       functionality. Next-hop label allocation also makes it necessary to
>>       carry the FEC in the fault detection message as the label alone is
>>       not sufficient to identify the LSP being verified.
>> ...
>>       i) LSP-Ping is used for boot-strapping the BFD session as described
>>       later in this document.
>>
>> There seem to be cases where there is no need for boot-strapping the BFD
>> session with LSP-Ping. For example, for PWs, both ends can start sending
>> BFD Control messages with Your Discr value of zero in an Active role, as
>> the PW Label provides the context to bootstrap the session.
>>
> 
> Please see below.
> 
>> ---
>>
>> 4. Theory of Operation
>>
>>       If there are multiple alternate paths from an ingress LSR to an
>>       egress LSR for a LDP IP FEC, LSP-Ping traceroute MAY be used to
>>       determine each of these alternate paths. A BFD session SHOULD be
>>       established for each alternate path that is discovered.
>>
>> There may also be multiple ECMPs for other FECs, like VPNv4/VPNv6
>> prefixes. Does this SHOULD apply to those as well?
> 
> No. As in those cases the ingress LSR knows the multiple paths and there
> is no need to use the LSP-traceroute mechanism.
> 
>> For other FECs, there
>> wouldn't be ECMPs (e.g., PWs RFC 4928), should that be explicitly mentioned?
>>
> 
> No. The above text applies only to the LDP ECMP case.

I meant for VPNv4 stacked over LDP FECs. Testing a VPNv4 FEC may result 
in multipaths from the underlying LDP ECMPs. Does the SHOULD apply in 
that case as well?

> 
>> ---
>>
>> 5. Initialization and Demultiplexing
>>
>>
>>     A BFD session may be established for a FEC associated with a MPLS
>>     LSP. As desribed above in the case of PHP and next-hop label
>>     allocation the BFD control packet received by the egress LSR does not
>>     contain sufficient information to associate it with a BFD session.
>>     Hence the demultiplexing MUST be done using the remote discriminator
>>     field in the received BFD control packet. The exchange of BFD
>>     discriminators for this purpose is described in the next section.
>>
>> 6. Session Establishment
>>
>>     To establish a BFD session a LSP-Ping echo
>>     request message MUST carry the local discriminator assigned by the
>>     ingress LSR for the BFD session. This MUST subsequently be used as
>>     the My Discriminator field in the BFD session packets sent by the
>>     ingress LSR.
>>
>> There seem to be other additional cases besides PHP where discriminators
>> need to be exchanged/boot-strapped (e.g., UHP and single label),
> 
> UHP is a valid case and I will mention it.
> 
>> but
>> situations where it's not needed (e.g., PWs). Should these cases be
>> enumerated/framed or clarified? Is this "MUST" (the first one in Section
>> 6) too strong considering cases where bootstrapping with LSP-Ping is not
>> needed (e.g., PWs) or should the MUST be conditioned to the cases where
>> is needed?
>>
> 
> For consistant operation of the BFD MPLS state machine the procedures in
> this document require LSP-Ping bootstrapping to all types of LSPs.
> Hence the text should stay as is.

But this adds a dependency on LSP-Ping that is not "required". Section 
3.2 of the document lists three functions for which LSP-Ping is used, 
that are not directly applicable to the PW case (a. and b. do not apply 
to PW LSPs, and c. is optionally applicable, but orthogonal/not tied to 
the BFD procedures).

> 
>> ---
>>
>> 6. Session Establishment
>>
>>     On receipt of the LSP-Ping echo request message, the egress LSR MUST
>>     send a BFD control packet to the ingress LSR.
>> ...
>> 7. Encapsulation
>>
>>     BFD control packets sent by the egress LSR are UDP packets. The
>>     source IP address is a routable address of the replier; the source
>>     port is the well-known UDP port 3784.  The destination IP address and
>>     UDP port MUST be copied from the source IP address and UDP port of
>>     the control packet received from the ingress LSR.
>>
>> LSP-Ping (ingress->egress) is used to exchange the ingress My
>> Discriminator. And then a BFD Control packet (egress->ingress) is used
>> to exchange the egress My Discriminator. Section 6 says that the egress
>> replies with a BFD Control packet (before it has received a BFD Control
>> packet from ingress), and Section 7 says that the egress copies the dest
>> UDP port from the source's ingress.
>> Therefore it seems that the
>> destination UDP Port of the first BFD Control packet (from egress to
>> ingress) is unspecified, and could be anything in the [49152 .. 65535]
>> range since:
>>
>>     The BFD control packet sent by the ingress LSR MUST be a UDP packet
>>     with a well known destination port 3784 [BFD-IP] and a source port
>>     assigned by the sender as per the procedures in [BFD-IP].
>>
>> Should the egress use also 3784 as destination port in the first BFD
>> Control packet?
> 
> Thanks for catching this bug. The egress should either use 3784 as the
> dest port if the return packet is being tunnelled. It should use 4784
> otherwise. I will clarify this.

Thanks. But in this case, if the packet is being tunneled, the BFD would 
have both udp.src and udp.dst as 3784, right? And if not tunneled, the 
pair 3794/4784, instead of using udp source from [49152 .. 65535].

> 
> 
>> Should the port be also included in the LSP-Ping
>> message? Or should the UDP port be allowed to change in the first packet
>> from the ingress->egress?
>> If the egress uses 3784 as dest UDP port, these two requirements from
>> [BFD-IP] seem to end up contradicting on this case:
>>
>>     The same UDP
>>     source port number MUST be used for all BFD Control packets
>>     associated with a particular session.  The source port number SHOULD
>>     be unique among all BFD sessions on the system.
>>     ...
>>     but the number of distinct uses of
>>     the same UDP source port number SHOULD be minimize
>>
>> So that would seem to leave the other two options (send the UDP Port in
>> the LSP-Ping, or allow for the UDP Port to change during the handshake.
>>
> 
> Specifying the dest port as 3784 or 4784 for the egress to ingress BFD
> packets addresses this.

 From ingress to egress, the spec says in Section 7:

    The BFD control packet sent by the ingress LSR MUST be a UDP packet
    with a well known destination port 3784 [BFD-IP] and a source port
    assigned by the sender as per the procedures in [BFD-IP].

And from egress to ingress, the spec says in Section 7:

    BFD control packets sent by the egress LSR are UDP packets. The
    source IP address is a routable address of the replier; the source
    port is the well-known UDP port 3784.

If from egress -> ingress the dest port is 3784 or 4784, it could end up 
with both fixed src and dst ports (in which it seems it does not address 
the two requirements from [BFD-IP]). Or how would the flow be in this case?

Should the egress instead send his own MyDisc in an LSP-Ping echo reply, 
and have the ingress send the first BFD Control message? Or the ingress 
communicate also its source port in the LSP-Ping echo?

> 
>> ---
>>
>> 7. Encapsulation
>>
>>     For MPLS PWs, alternatively,
>>     the presence of a fault detection message may be indicated by setting
>>     a bit in the control word [VCCV].
>>
>> This procedure needs signaling or static configuration to create the
>> VCCV control channel before BFD packets could be exchanged over the
>> control channel (with the bit in the CW). Are more details needed?
> 
> I will specify that the two ends in this case are assumed to be configured
> to use this control channel. And signaling this capability is outside the
> scope of this document.

That would address the CC Type, but not the CV Type.

> 
>> See
>> below as well.
>>
>> ---
>>
>> 7. Encapsulation
>>
>>       In this case the destination IP address, used in a
>>       BFD session established for one such alternate path, is the address
>>       in the 127/8 range discovered by LSP-ping traceroute [RFC4379] to
>>       exercise that particular alternate path.
>>
>> A nit, where it says "is the address", there may be (and typically will
>> be) multiple addresses from 127/8 to exercise a particular ECMP. Should
>> that say "is one address from the 127/8 ... that exercises..."?
>>
> 
> No. It is a particular address discovered for that path. The current text
> is correct.

But multiple addresses can be discovered for that path in the Multipath 
Information field, "a particular address" is not "the address". Just a 
nit though.

> 
>> Also, there is no mention of BFD Echo adjunct function to the
>> asynchronous mode.
>>
> 
> I will specify that the echo function is out of scope.
> 
>> ---
>>
>> 11.2. Informative References
>>
>>       [VCCV]     T. Nadeau, C. Pignataro, R. Aggarwal,
>>                  "Pseudo Wire (PW) Virtual Circuit Connection Verification
>>                  ((VCCV)", draft-ietf-pwe3-vccv-13.txt
>>
>> This reference points to rev 13 of this document. In the subsequent
>> revision, this document was split into what resulted in RFC 5085 and the
>> ID draft-ietf-pwe3-vccv-bfd. It seems that some citations refer to the
>> former, while others to the latter, and they appear to be made in a
>> Normative fashion (e.g., because the VCCV control channel needs to exist
>> in order to send BFD packets over it).
>> However, given that PWs need an associated VCCV control channel, do not
>> need LSP-Ping boot-strapping (as can get the context from the PW label),
>> should this document point to draft-ietf-pwe3-vccv-bfd (that goes into
>> different BFD functional modes) for the PW case instead of also defining
>> it here, since it has a number of specific unique issues?
>>
> 
> This document simply needs to point to RFC 5085 for the control word based
> control channel.

Yes, for the control channel, but it would still lack the connectivity 
verification (CV) types.

> 
> "The use of BFD for PWs is further described in [VCCV] and [OAM-MAP]."
> 
> It should point to draft-ietf-pwe3-vccv-bfd in the above statement
> in section 3.1

I think there's one problem and two limitations with that approach. The 
issue is that, for BFD to be run over the control-channel, it would need 
to define the CV Type(s)/payload type(s) for BFD (as a normative 
procedure). The limitations are that, for the PW case there is no 
requirement to use LSP-Ping to bootstrap the session (and can remove the 
dependency on LSP-Ping for the PW case), and the other limitation is 
regarding alternate encapsulations for BFD (PW-ACH mode, and functional 
modes specified as different CV Types as well).

Thanks again,

--Carlos.

> 
> rahul
> 
> 
>> Thanks,
>>
>> --
>> --Carlos Pignataro.
>> Escalation RTP - cisco Systems
>>
>>
>>
>>
> 

-- 
--Carlos Pignataro.
Escalation RTP - cisco Systems

---

From: Rahul Aggarwal <[email-masked]>
Date: Mon, 5 May 2008 16:54:28 -0700 (PDT)

Hi Carlos,

<snipped>

> in multipaths from the underlying LDP ECMPs. Does the SHOULD apply in

No.

> to PW LSPs, and c. is optionally applicable, but orthogonal/not tied to

Section 3.2 states the following that applies to PWs:

"In addition to
   this presence of the FEC in the echo request message makes it
   possible to verify the control plane against the data plane at the
   egress LSR."

> pair 3794/4784, instead of using udp source from [49152 .. 65535].

No. The modified text will say the following:

"The BFD control packet sent by the egress LSR MUST have a well known
destination port 4784, if it is routed [BFD-MHOP], or it MUST have a
well known destination port 3784 [BFD-IP] if it is encapsulated in a
MPLS label stack. The source port MUST be assigned by the egress lSR
as per the procedures in [BFD-IP]."

>     assigned by the sender as per the procedures in [BFD-IP].

This is correct.

> the two requirements from [BFD-IP]). Or how would the flow be in this case?

See above for the modified text. The intention was to use the source port
as in [BFD-IP].

> That would address the CC Type, but not the CV Type.

This draft applies to *only* BFD for MPLS LSPs. Hence the CV type
discussion is simply not relevant.

> Yes, for the control channel, but it would still lack the connectivity

This draft specifies procedures for *only BFD*. Hence the entire
CV type discussion is simply not relevant.

> procedure).

As I said this draft specifies fully standalone procedures to run BFD over
a MPLS LSP including PWs. For a bidrectional LSP both
ends are supposed to be configured for BFD.

Signaling BFD as a CV type is certainly not required for the procedures in
this draft.

> The limitations are that, for the PW case there is no
> dependency on LSP-Ping for the PW case),

For the procedures in this draft bootstrapping using LSP-Ping is a MUST.
As for reasons for using LSP-Ping for PWs in conjunction with BFD see
section 3.2:

""In addition to
   this presence of the FEC in the echo request message makes is
   possible to verify the control plane against the data plane at the
   egress LSR."

> and the other limitation is

The use of PW-ACH is spelled out in RFC5085. The use of other CV types is
simply not relevant to this draft as it covers only BFD.

rahul

---

From: Carlos Pignataro <[email-masked]>
Date: Tue, 06 May 2008 14:51:00 -0400

Hi Rahul,

Thanks, please see inline.

>    possible to verify the control plane against the data plane at the

Yes, but Section 3.1 says the following:

    In addition LSP-Ping also
    provides a mechanism for verifying the MPLS control plane against the
    data plane.
    [...]
    BFD cannot be used for verifying the MPLS control plane against the
    data plane.  However BFD can be used to detect a data plane failure
    in the forwarding path of a MPLS LSP.
    [...]
    LSP-Ping includes extensive control plane verification. BFD on the
    other hand was designed as a light-weight means of testing only the
    data plane. As a result, LSP-Ping is computationally more expensive
    than BFD for detecting MPLS LSP data plane faults. BFD is also more
    suitable for being implemented in hardware or firmware due to its
    fixed packet format. Thus the use of BFD for detecting MPLS LSP data
    plane faults has the following advantages:
    [...]
    There may be other potential cases where fast failure detection is
    desired for MPLS LSPs.

The control-plane verification is inherent to LSP-Ping, and orthogonal 
to running BFD over the PW. It's not an inherent dependency (running 
LSP-Ping independent of BFD seems to achieve the same).

> as per the procedures in [BFD-IP]."

Thanks. That clarifies.

Regarding IP addresses, that para would continue with something like 
this, right?

    The source IP address is a routable address of the replier.  The
    destination IP address MUST be copied from the source IP address of
    the LSP-Ping echo request message received from the ingress LSR.

Also, I just noticed that the regarding the TTL, the text says (does it 
apply to both directions since it's in a separate para?):

    The IP TTL MUST be set to 1.

Is this done intentionally to ensure intercepting the packet to the 
control plane in the ingress -> egress direction (even with the 
destination in 127/8)? If so, could the Security Considerations mention 
that the GTSM is not in effect in that direction, and with a routed 
multi-hop reply? Or should it be set to 255 and GTSM-checked on receipt? 
And in the egress -> ingress direction, should the TTL be set to 255 
(and checked for GTSM if the dest port if 3784, but not if the dest port 
is 4784)?

Please see below.

> Signaling BFD as a CV type is certainly not required for the procedures in

If this specification makes use of the control channel from RFC5085 for 
PW LSPs, only fault detection message payload types that are signaled 
and agreed as CV types can run over the control channel, from RFC5085.

>    possible to verify the control plane against the data plane at the

Yes. Agreed.

Along these lines, the Session Establishment procedures in Section 6 say:

    On receipt of the LSP-Ping echo request message, the egress LSR MUST
    send a BFD control packet to the ingress LSR.  This BFD control
    packet MUST set the Your Discriminator field to the discriminator
    received from the ingress LSR in the LSP-Ping echo request message.

I think this should additionally require successful FEC Validation 
("Validate FEC Stack" flag in the MPLS echo request) before sending a 
BFD control packet back, or at least a successful (return-code 3) label 
operation check on receipt of the MPLS Echo request.

> simply not relevant to this draft as it covers only BFD.

LSP-Ping over PW-ACH is defined in RFC5085, so the LSP-Ping CV Type is 
relevant for the PW case, or it could not bootstrap the session. From 
RFC5085, for other connectivity-verification/payload types (like BFD) 
over the PW-ACH, a CV Type is needed.

The procedures in this draft strictly seem to update these rules, with 
an implicit CV Type "negotiation"/agreement by means of sending (at the 
ingress LSR) and parsing/understanding (at the egress LSR) the BFD 
Discriminator TLV in the MPLS Echo request. There is the bootstrapping 
(and LSP-Ping as a CV Type over the PW-ACH should have been negotiated 
before this can happen for the PW case from RFC5085) as a "negotiation", 
so there wouldn't be unexpected CV Types/payloads received (if the BFD 
TLV is not supported it would result in "TLV not understood" since it's 
15). But I think this would need to be spelled out.

Thanks,

--Carlos.

---

From: Rahul Aggarwal <[email-masked]>
Date: Tue, 6 May 2008 17:40:58 -0700 (PDT)

Hi Carlos,

We are down to a couple of points. Please see below:

<snipped>

>     the LSP-Ping echo request message received from the ingress LSR.

Something like that, yes.

> destination in 127/8)?

Look at section 4.4 of RFC4379. I will add a reference to that.

>If so, could the Security Considerations mention

The revised text will make it clear that for a routed reply
[BFD-MHOP] applies and otherwise [BFD-IP] applies. I don't think
there is any need to state the above here.

<snipped>

Please see below.

> >    possible to verify the control plane against the data plane at the

Great.

> operation check on receipt of the MPLS Echo request.

This is normal LSP-Ping procedure.

> 15). But I think this would need to be spelled out.

How about inserting the following text to clarify this:

"To enable fault detection procedures specified in this document, for a
particular MPLS LSP, this document requires the ingress and
egress LSRs to be configured. This includes configuration for supporting
BFD and LSP-Ping as specified in this document. It also includes
configuration that enables to the ingress LSR to determine the
method used by the egress LSR to identify OAM packets e.g. whether the TTL
of the innermost MPLS label needs to be set to 1 to enable the egress LSR
to identify the OAM packet. This applies to fault detection for MPLS PWs
as well. Extending [RFC5085] procedures to signal BFD capability
between PW endpoints is outside the scope of this document."

rahul

---

From: Carlos Pignataro <[email-masked]>
Date: Wed, 07 May 2008 14:54:57 -0400

Hi Rahul,

> We are down to a couple of points. Please see below:

Yes, thank you for your responses and revisions. Please see inline.

> Look at section 4.4 of RFC4379. I will add a reference to that.

OK, thanks. (I was asking because the IP TTL 1 processing exception does 
not apply to the e2e PW case, and there is the PW-ACH exception)

> there is any need to state the above here.

Thanks. Would this apply only to encapsulation (since the text is within 
the Encapsulation section), or also to the GTSM procedures from 
[BFD-IP]? Could that be clarified as well, since it might not be 
directly apparent?

> This is normal LSP-Ping procedure.

The normal LSP-Ping procedure generates an LSP-Ping reply with a result 
code that could differ from "AOK", and could for example be "Replying 
router has no mapping for the FEC at stack-depth <RSC>" or "No label 
entry at stack-depth <RSC>"; in these cases, in the new procedures, I 
think that the egress LSR should not send a BFD control packet (as there 
is a FEC<->Label mismatch detected, and the feature of using LSP-Ping 
with BFD so that "the presence of the FEC in the echo request message 
makes is possible to verify the control plane against the data plane at 
the egress LSR" would become a NOOP). Shouldn't the BFD session be 
bootstrapped only after a successful control-plane checking (and ideally 
including FEC Validation)?

> configuration that enables to the ingress LSR to determine the
                ^
                or signaling

> as well.

"For fault detection for MPLS PWs, this document also assume that a PW 
control channel (e.g., a PW-ACH) and support for LSP-Ping are provided 
prior to initializing the procedures specified in this document, as 
specified in [RFC5085]. "

or something along those lines.

> Extending [RFC5085] procedures to signal BFD capability

Should this pointer to [RFC5085] be normative, and the one to 
pwe3-vccv-bfd in "The use of BFD for PWs is further described in [VCCV] 
and [OAM-MAP]." be informative?

Thanks,

--Carlos.

---

From: Rahul Aggarwal <[email-masked]>
Date: Wed, 7 May 2008 13:00:05 -0700 (PDT)

Hi Carlos,

<snipped>

> [BFD-IP]? Could that be clarified as well, since it might not be

I will clarify this.

<snipped>

> including FEC Validation)?

I see there is value in clarifying this. Will do.

<snipped>

> > configuration that enables to the ingress LSR to determine the

The whole point is that this document does not specify any signaling to
discover the ingress/egress capabilities. It relies on configuration.

> or something along those lines.

I don't think that makes sense as this document relies on configuration.
Further there is no point in signaling LSP-Ping capability if BFD
capability cannot be signaled.

I fail to see why it is not enough to spell out that this document
requires configuration. It doesn't preclude capability signaling to be
added by another document.

> and [OAM-MAP]." be informative?

Both should be informative pointers.

rahul

---

From: Nadeau Thomas <[email-masked]>
Date: Wed, 7 May 2008 17:02:07 -0400

> added by another document.

	I agree for the static case things are explicitly configured.  
However, I think the confusion here lies in the fact that we could  
configure the capability, and then advertise the BFD/VCCV capability,  
right? But those are explicitly detailed in the vccv-bfd document  
(draft-ietf-pwe3-vccv-bfd-01).  It might be most appropriate to simply  
remove the forward reference to the vccv-bfd stuff from here, and only  
refer to this document from there.

	--Tom

---

From: Rahul Aggarwal <[email-masked]>
Date: Wed, 7 May 2008 16:49:23 -0700 (PDT)

Hi Tom,

Please see below:

<snipped>

<rahul>
> > added by another document.

<tom> 	I agree for the static case things are explicitly configured.

We are in sync. This is the key point.

tom>
> right?

This spec requires configuration and should just say that signaling of
capabilities is out of scope.

tom>
> But those are explicitly detailed in the vccv-bfd document

How about removing the forward reference to draft-ietf-pwe3-vccv-bfd-01.
But leaving the reference to RFC5085 to say that there could be
other ways to identify OAM packets other than ttl=1, for PWs ? And let
that be an informative reference ?

rahul

---

From: Carlos Pignataro <[email-masked]>
Date: Thu, 08 May 2008 14:50:47 -0400

Hi Rahul, Tom,

Please find some comments inline on the last point (down to one).

>> I don't think that makes sense as this document relies on

That's fine, but my point is that instead of configuration, this 
document (for the PW case) relies on the existence of a control channel 
and capability/ability/agreement to run LSP-Ping, which in turn can be 
preformed by configuration (or other means equally).

> <tom> 	I agree for the static case things are explicitly configured.

Please note that I'm not referring to signaling the BFD procedures on 
this document. But these BFD procedures, for PWs, start with a control 
channel and LSP-Ping (signaled or configured), both defined in RFC5085.

> capabilities is out of scope.

Note that RFC5085 says:

    Routers that implement VCCV create a Control Channel (CC) associated
    with a pseudowire.  This control channel can be signaled (e.g., using
    LDP or L2TPv3 depending on the PWE3) or statically configured.  Over
    this control channel, VCCV Connectivity Verification (CV) messages
    are sent.

I mean (and I may not have been clear), not to signal capabilities for 
the procedures in this spec, but the configuration or signaling 
pre-requisite (and hence Normative for PWs) to start those procedures in 
this document (with LSP-Ping over the PW control channel).

For the PW case specifically,  a control channel needs to exist prior to 
OAM messages. This dependency can be realized by configuration or 
signaling. For example, the text says as an example use TTL=1 or:

But to use this method, it needs to be signaled or configured as per 
RFC5085, otherwise OAMs could potentially be not intercepted and 
forwarded to the CE. The TTL=1 listed is another control channel type 
from RFC5085.

> other ways to identify OAM packets other than ttl=1, for PWs ? 

Note that TTL=1 for PWs is one of the RFC5085 control channels, so it 
seem that RFC5085 is needed to bootstrap:

          Bit 2 (0x04) - Type 3: MPLS PW Label with TTL == 1

But regarding this forward pointer, my preference would be to leave it 
in (for completeness and cross-reference) in the same context as the 
existing text:

	"Use of BFD for PWs is further described in [VCCV-BFD] and
	[OAM-MAP].".

Thanks,

--Carlos.

> And let

---

From: Rahul Aggarwal <[email-masked]>
Date: Thu, 8 May 2008 16:13:17 -0700 (PDT)

Hi Carlos,

> preformed by configuration (or other means equally).

And those other means are out of scope. Seems like we are in agrement and
are saying the same thing. Let us not spin in wordsmithing.

> signaling. For example, the text says as an example use TTL=1 or:

And this spec requires configuration. That is it.

> forwarded to the CE. The TTL=1 listed is another control channel type

And the revised text that I had sent makes it clear that this needs to be
configured.

>           Bit 2 (0x04) - Type 3: MPLS PW Label with TTL == 1

See above note on configuration.

> 	"Use of BFD for PWs is further described in [VCCV-BFD] and

Based on Tom's comment, I am inclined to keep only RFC5085 as an
informative reference, unless I hear more opinions on this.

I will produce a revised ID. Thanks for the comments.

rahul