RE: [PWE3] status signalling of MPLS PW state

["Hamid Ould-Brahim" <hbrahim@nortelnetworks.com>]

Luca,

 

> yes , i did that , look in the iana draft, it's in there. I
> left it in this
> thread for discussion only.

Okay. I looked at the PW-IANA draft. I think that part needs

to be reworked in order to reflect exactly the usage of the

status field.

 

In pw-iana draft:

 

"   As specified in [1], a new PW status TLV contains a 32 bit field, PW
   status value 0 is reserved to clear all failures. PW Status Bits 0
   through 4 are defined in this document. PW Status Bits 6 through 15
   are to be assigned by IANA using the "IETF Consensus" policy defined
   in RFC2434. PW Status Bits 16 through 23 are to be assigned by IANA,
   using the "First Come First Served" policy defined in RFC2434. PW
   Status Bits 24 through 31 are vendor-specific, and values in this
   range are not to be assigned by IANA.

   PW status is a 4 octet bit field as follows:

           0x00000000 - Pseudo Wire forwarding ( clear all failures )
           0x00000001 - Pseudo Wire Not Forwarding
           0x00000002 - Local Customer-facing PW ( ingress ) Receive Fault
           0x00000004 - Local Customer-facing PW ( egress ) Transmit Fault
           0x00000008 - Local PSN-facing PW ( ingress ) Receive Fault
           0x00000010 - Local PSN-facing PW ( egress ) Transmit Fault"

 

Since the structure is a bit field and since in that

structure some bits/set of bits are reserved. The above codepoints

do not exactly reflect the intent. For example,

it is not that 0x00000002 that makes the local customer-facing PW

receive fault but it is the setting of bit number 1 that indicates

this problem is happening.

 

I suggest to layout the bit structure with each bit having its own

description. Using the pw-IANA description above (btw I think there is

a typo with respect to bit number 5 which appears as 6 in the iana draft),

my suggestion is to rewrite the above to:

 

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |N|I|E|R|T|  IANA ASSIGNED      |   IANA FCFS   |     VENDOR    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   N: The "not forwarding bit". When this bit is set, it indicates the
      PE sending the status is in "not forwarding" state.
   I: Local Customer-facing PW ( ingress ) Receive Fault
   E: Local Customer-facing PW ( egress ) Transmit Fault
   R: Local PSN-facing PW ( ingress ) Receive Fault
   T: Local PSN-facing PW ( egress ) Transmit Fault

   A value of 0x00000000 is reserved and indicates that the status
   of the Pseudo-wire is forwarding.

 

   Obviously the NIERT bits can be set independently (and that

   makes status combination).

Hamid.