Re: Ben Campbell's Discuss on draft-ietf-bfd-seamless-ip-04: (with DISCUSS and COMMENT)

["Ben Campbell" <[e-mail]>]

Hi Carlos,

Thanks for the response. One question in-line (I removed sections that 
seem closed.):

Thanks!

Ben.


On 3 May 2016, at 20:12, Carlos Pignataro (cpignata) wrote:


[...]

>> ----------------------------------------------------------------------
>> DISCUSS:
>> ----------------------------------------------------------------------
>>
>> Section 4, 2nd paragraph: "  If the port is not 7784, then the packet
>> MUST be looked up to locate
>>   a corresponding SBFDInitiator session or classical BFD session 
>> based
>>   on the value from the "your discriminator" field in the table
>>   describing BFD discriminators.  "
>>
>> Do I understand correctly that whether or not the destination port is
>> 7784 tells you if this is an "initial" packet vs a "reflected" 
>> packet? If
>> the destination port is not 7784, how do you know it’s not some 
>> competely
>> different protocol? Do you assume the receiver has no other UDP based
>> services?
>>
>
> Alia caught the same thing. The text is currently kinda broken as 
> written in rev -04.
>
> We fixed this as follows based on Alia’s discuss, from our working 
> copy:
>
>    This procedure for an S-BFD packet is executed on both the 
> initiator
>    and the reflector.  If the port is 7784 (i.e., S-BFD packet for
>    S-BFDReflector), then the packet MUST be looked up to locate a
>    corresponding SBFDReflector session based on the value from the 
> "your
>    discriminator" field in the table describing S-BFD discriminators.
>    If the port is not 7784, but the packet is demultiplexed to be for 
> an
>    SBFDInitiator, then the packet MUST be looked up to locate a
>    corresponding SBFDInitiator session based on the value from the 
> "your
>    discriminator" field in the table describing BFD discriminators.  
> In
>    that case, then the destination IP address of the packet SHOULD be
>    validated to be for itself.  If the packet demultiplexes to a
>    classical BFD session, then the procedures from [RFC5880] apply.
>
> Which should clarify your point as well.

I think it does, and will clear the discuss.  For my own curiosity: do I 
understand correctly, that the non 7784 port would be a port that a 
reflector learned from the source-port of an initiator message, which by 
necessity be listening for S-BFD packets (based on your answer below 
about an initiator listening on it's source port?

[...]