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

From: "HariKishan" <[email-masked]>
Date: Mon, 20 Aug 2001 09:55:16 -0700

Q1::

Section 3.4.5.1.2 LDP RFC 3036 states that, when a label mapping
message
is received with a path vector 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 Hop Count TLV is present
in the Label Request/Mapping message. ( CRa.1)

Does that mean Loop Detection can be used only along with Hop Count
and it can't be used independently ( without Hop Count )?? I know that
sometimes (for ATM/FR LSRs) Hop Count 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 any other loop detection mechanism ( like Hop Count). This
contradicts

with the description of Check_Received_Attributes (Cra.1) Algorithm

in RFC 3036 which states that Path Vector TLV will not be processed

if there is no Hop Count TLV in the received message.

*******

Thanks,
HariKishan

---------------------------------
HariKishan Desineni,
Ericsson Inc,
Data Backbone & Optical Division,
Santabarbara,
California - 93117
Office:(805) 562 6419
Home:(805) 562 8841