Subject: Questions on Loop Detection (Cra.1, etc.,)

From: "kishan" <[email-masked]>
Date: Sun, 19 Aug 2001 10:44:27 -0700

Q1::

Section 3.4.5.1.2 LDP RFC 3036 states that, when a label mapping message 
is received with a pathvector TLV and loop is detected, the LSR should transmit
 a label release message carrying a Status TLV to the sending LSR to signal
"Loop Detected".

 But,the Label release message(3.5.11) does not include a status TLV in it's
optional List of TLVs? So, what is the way to inform downstream that the 
label release was a result of loop detected by the upstream??

*****

Q2::

    Check_Received_Attributes (A.2.6) algorithm is in such a way that the 
 Path Vector TLV will be processed only when HopCount TLV is present 
in the Label Request/Mapping message. ( CRa.1)

Does that mean Loop Detection can be used only along with HopCount
and it can't be used independently ( without HopCount )?? I know that
sometimes (for ATM/FR LSRs) HopCount is a MUST in Label Request
messages and HC may or may not be present in Label mapping messages
based on the Merge type of the LSR.

The LDP MIB  "draft-ietf-mpls-ldp-mib-07.txt" has the following
loop detection capabilities.
" mplsLdpLsrLoopDetectionCapable OBJECT-TYPE

SYNTAX INTEGER {

none(1),

other(2),

hopCount(3),

pathVector(4),

hopCountAndPathVector(5)

}"

which implies that pathVector(4) should be configurable independent 

of anyother loop detection mechanism ( like HopCount). This contradicts

with the description of Check_Received_Attributes (Cra.1) Algorithm 

in RFC 3036 which states that PathVector TLV will not be processed

if there is no HopCount TLV in the received message.

*******

Thanks,
HariKishan

---

From: Vasanthi Thirumalai <[email-masked]>
Date: Mon, 20 Aug 2001 18:03:34 -0400

Harikishan,
The Status TLV in this case is carried as an optional parameter in the Label
release message. In such a usage, the U-bit of the Status TLV should be set
to 1 to indicate that the receiver should silently discard the TLV if
unprepared to handle it.
-Vasanthi

-----Original Message-----
From: kishan [mailto:[email-masked]]
Sent: Sunday, August 19, 2001 1:44 PM
To: [email-masked]
Subject: Questions on Loop Detection (Cra.1, etc.,)

Q1::
 
Section 3.4.5.1.2 LDP RFC 3036 states that, when a label mapping message 
is received with a pathvector TLV and loop is detected, the LSR should
transmit
 a label release message carrying a Status TLV to the sending LSR to signal
"Loop Detected".

*****
 
Q2::

 

SYNTAX INTEGER {

none(1),

other(2),

hopCount(3),

pathVector(4),

hopCountAndPathVector(5)

}"

*******

Thanks,
HariKishan