Subject: [mpls] Some doubts in RFC 6371 and RFC 6428

From: Chao Fu <[email-masked]>
Date: Thu, 29 Dec 2011 10:51:00 +0800

Hi all,

I have some doubts on RFC 6371 "OAM Framework for MPLS-Based Transport" and
RFC 6428 "CC, CV, and RDI for MPLS-TP".  Who can help me to clarify them?
Thanks a lot!

1. Section 5.1.1.3 of RFC 6371 defines Period Misconfiguration Defect:
   If proactive CC-V OAM packets are received with the expected globally
   unique Source MEP identifier but with a transmission period different
   than the locally configured reception period, then a CC-V period
   misconfiguration defect is detected.
   o  Entry criteria: A MEP receives a CC-V proactive packet with the
      expected globally unique Source MEP identifier but with a
      transmission period different than its own CC-V-configured
      transmission period.

   My doubt:* It is said to compare with the locally configured reception
period in the definition, but in the Entry criteria, it is compared with it
own CC-V-configured transmission period. Are they same? Just because these
two values should be same? For LOC in 5.1.1.1, it also uses the receiving
MEP's configured CC-V reception period.*
*   And such Period Misconfiguration Defect is not defined in RFC 6428.
Does MPLS TP need it? Why it is not in RFC 6428?
*
2. In 5.1.2 of RFC 6371:
   If a MEP detects a LOC defect that is not caused by a period
   misconfiguration, it should block all the traffic (including also the
   user data packets) that it receives from the transport path, if this
   consequent action has been enabled by the operator.

   *My doubt: Does it mean the period misconfiguration should or might
cause the LOC? Will the packets be discarded? If not, there should not be
LOC. My opinion is that the period misconfiguration should not cause LOC.
*
3. In 5.1.3 of RFC 6371:
   Note that the reception period is the same as the configured
transmission rate.

   *My doubt: Does it mean no need to configure reception period? But many
places mention "configured reception period", do they mean the configured
transmission rate?

*4. In 3.7.3 of RFC 6428:
  It will also communicate session DOWN to its session peer using CC
messages.

  *My doubt: Does it mean only notify the peer to bring the session DOWN
but the local session will not be DOWN? Or we should bring the local
session DOWN also? But it is not in the BFD State machine of Figure 7.

*5. In 3.7.1 of RFC 6428: Session Initiation and Modification

   Session initiation occurs starting from MinRx = 1 second, MinTx >= 1
   second, and the detect multiplier = 3.

   Once in the UP state, Poll/Final discipline is used to modify the
   periodicity of control message exchange from their default rates to
   the desired rates and to set the detect multiplier to 3.

   *My doubt: Does it mean the BFD session will not be started with the
configured values but use the default values? What the values will be
filled in the packet? The default ones or the configured values?
   Why need P/F here? There is no timer negotiation. I think here the
configured transmission rates should be same on both Engpoints, otherwise
there are Period Misconfiguration Defects defined in 5.1.1.3 of RFC 6371.

*--
Regards
Chao Fu