Some draft-ietf-bfd-base-06.txt Queries

[aaron_castellino <[e-mail]>]

Just some implementation queries!

4.1. Generic BFD Control Packet Format
===========================

1.   Desired Min TX Interval

      This is the minimum interval, in microseconds, that the local
      system would like to use when transmitting BFD Control packets.
      The value zero is reserved.
      
Q. Why is the value zero reserved. What happens if I get a packet with this
value as zero. Should it be discarded. if so then why is it reserved?

2.   Required Min RX Interval

      This is the minimum interval, in microseconds, between received
      BFD Control packets that this system is capable of supporting.  If
      this value is zero, the transmitting system does not want the
      remote system to send any periodic BFD Control packets.

Q. Shouldn't it be that if this this value is zero and demand mode bit is
set then the transmitting system does not want the receving system to send
packets. Along with this, if demand mode bit is not set, shouldnt the
received packet be discarded.What is the requirement of a sending system to
send a BFD control packet with this feild as zero in Async mode.

6.6
====
3. Note that if Demand mode is enabled in only one direction, continuous  
       bidirectional connectivity verification is lost (only connectivity in  
       the direction from the system in Demand mode to the other system will  
       be verified.)  Resolving the issue of one system requesting Demand  
       mode while the other requires continuous bidirectional connectivity  
       verification is outside the scope of this specification. 

Q .if a system wants to support only Asyncronous mode and will discard
demand mode packets? What happens in this situation? 
Since now each system can independently support demand mode, wouldnt it be a
problem for systems not supporting demand mode. I asume in this case the
system in this case
cannot even inform the other station that demand mode is not supported

6.8.3
====
4. If either bfd.DesiredMinTxInterval is changed or
   bfd.RequiredMinRxInterval is changed, a Poll Sequence MUST be
   initiated (see section 6.5).
   
In any case other than those explicitly called out above, timing
   parameter changes MUST be effected immediately (changing the
   transmission rate and/or the Detection Time), and a Poll Sequence
   SHOULD NOT be sent.
   
Q. Considering the above 2 statements what are the cases in which timing
parameters can be sent without poll bit set?
It seems there is no such situation except for detection time change which
does not require poll bit to be set.

6.8.7
=====          
5. A system MUST NOT periodically transmit BFD Control packets if  
       bfd.RemoteMinRxInterval is zero. 

Q. Should not this be only in demand mode? In Async mode how is this
possible?What is the purpose of this?
In Async mode if this is true, how does the state machine work, timers,
intervals etc?

Regards
/Aaron
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