Subject: [mpls] One question about U and F-bit for Status TLV

From: Mach Chen <[email-masked]>
Date: Mon, 17 Jan 2011 17:16:09 +0800

Hi,

I have one question about U and F-bit setting for Status TLV.

In Section 3.3, the F-bit of a TLV is defined as:
"F-bit
      Forward unknown TLV bit.  This bit applies only when the U-bit is set 
and the LDP message containing the unknown TLV is to be forwarded. ..."

And in Section 3.4.6.
The definition of Status TLV says:
"U-bit
      SHOULD be 0 when the Status TLV is sent in a Notification message.
      SHOULD be 1 when the Status TLV is sent in some other message.
F-bit
      SHOULD be the same as the setting of the F-bit in the Status Code 
field."

So, for a Notification message contained Status TLV, the F-bit of Status TLV 
should make no sence. And if an LSR receives a Nofication message and it 
does not know the Status TLV, the entrie Notification message MUST be 
ignored.

But following up, the Status Code defines:
"F-bit
      Forward bit.  If set (=1), the notification SHOULD be forwarded to the 
LSR for the next-hop or previous-hop for the LSP, if any, associated with 
the event being signaled.  If clear (=0),the notification SHOULD NOT be 
forwarded."

It seems that it wants to use the F-bit to control whether to forward the 
notification messsage, but this should not work since the U-bit is clear.

I am not sure which is the intent of the specification. I'd appreciate that 
someone clarify this!

Best regards,
Mach

---

From: Mach Chen <[email-masked]>
Date: Mon, 17 Jan 2011 17:54:27 +0800

The question is about RFC5036

Best regards,
Mach

--------------------------------------------------
From: "Mach Chen" <[email-masked]>
Sent: Monday, January 17, 2011 5:16 PM
To: <[email-masked]>
Subject: [mpls] One question about U and F-bit for Status TLV

> So, for a Notification message contained Status TLV, the F-bit of Status 
> TLV should make no sence. And if an LSR receives a Nofication message and 
> it does not know the Status TLV, the entrie Notification message MUST be 
> ignored.
>
>      Forward bit.  If set (=1), the notification SHOULD be forwarded to 
> the LSR for the next-hop or previous-hop for the LSP, if any, associated 
> with the event being signaled.  If clear (=0),the notification SHOULD NOT 
> be forwarded."
>
> I am not sure which is the intent of the specification. I'd appreciate 
> that someone clarify this!
>
> Best regards,
> Mach
>
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