Re: [PWE3] status signalling of MPLS PW state

[Luca Martini <luca@level3.net>]

Today's revision has the following fixes:

- replaced CE with CE-Facing
- PW FEC should not contain interface parameters
- faults can be cleared by clearing respective bits.

Outstanding issues:
- TLV value needs coordination/lookup appropriate one.

- how to make this work better with label withdraw mode.
- Ignore Bit: should it be set ?

Other points :

- I really would like not to have this be flexible to allow an infinite amount 
of status messages allocated without WG study and RFC update and proper 
documentation.

- the "let's split it because we can't agree" method has been exhausted. I do 
not believe that there is much support for creating any more drafts from splits.

- can somebody enumerate any faults that are not included here , that a PW can 
experience ?

In general we initially reserved the PW FEC, and interface parameters, for PW 
specific information , that would not change, and if incompatible it would 
cause an error and the PW would not be enabled.
Special information such as IP addresses, and QoS congestion messages, Qos 
requests ..etc that CAN change once the PW is operational need to be in a 
different message. NOT a label mapping message ! We could call this message a 
PW dynamic parameter ( or some better name, below called the PW link status 
message ) and this is mostly what is in draft-shah. The status of the PW should 
be a TLV in this message. OTher TLVs will specify other proprieties of the PW.
we then spec the status TLV, and message in this draft , and the other TLVs 
elsewhere.


This thread is very constructive , thanks for all the reading and comments.

Luca

this is today's version, tomorrow will definitely be different .....

.Pb "Signaling of Pseudo Wire Link Status"

.Pc "Use of Label Mappings."
The PEs MUST send PW label mapping messages to their peers as soon as the PW
is configured and administratively enabled, regardless of the CE-facing interface
state. The PW label should not be withdrawn unless the user administratively
configures the CE-facing interface down (or the PW configuration is deleted
entirely).
A simple label withdraw method SHOULD also be supported as an alternative.

.Pc "Signaling PW Link status."
When PWLE mode is in use, the PE devices use a new LDP TLV to
indicate status to their remote peers, instead of withdrawing their
PW FEC labels.  This Link Status TLV contains more information than
the simple Label Withdraw message used in the baseline signaling.

The format of the Link Status TLV is:
.DS 0 0
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|   Link Status (0x0700)    |      Length                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Status Code           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.DE

Where status is a 2 octet bit field:

.nf
0x0000 - Pseudo Wire forwarding ( clear all failures )
0x0001 - Pseudo Wire Not Forwarding
0x0002 - Local Customer-facing Interface Receive Fault
0x0004 - Local Customer-facing Interface Transmit Fault
0x0008 - Local Core-facing Interface Receive Fault
0x0010 - Local Core-facing Interface Transmit Fault
.En

The above status codes can be logically combined to indicate more then a
single failure at once. Each fault can be cleared by sending an appropriate
status message with the respective bit cleared.

The presence of the lowest bit (PW Not Forwarding) acts only as a
generic failure indication when there is a link-down event for
which none of the other bits apply.


The Link Status TLV is transported to the remote PW peer via a new
LDP message, the PW Link Status Message.

The format of the PW Link Status Message is:

.DS 0 0
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|   PW Link Status (0x0700)   |      Message Length           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Message ID                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           PW FEC TLV                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Link Status TLV                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.DE

The PW FEC TLV SHOULD not include the interface parameters as they are
ignored in the context of this message. When a PE's CE-facing interface
encounters an error, use of the new message allows the PE to send a single
Link Status message, using a PW FEC TLV with only the group ID set, to
denote this change in status for all affected PW connections.



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