Re: [dhcwg] Adam Roach's No Objection on draft-ietf-dhc-relay-port-07: (with COMMENT)

["Naiming Shen (naiming)" <[e-mail]>]

Hi Adam,

> On Nov 29, 2017, at 11:48 AM, Adam Roach <[e-mail]> wrote:
> 
> Naiming --
> 
> Thanks for your quick reply. I had to do a bit more reading about DHCP relay behavior to understand your response to my third point, but it all seems to make sense now. I appreciate your taking the time to clarify. It might be helpful to extend the final paragraph in the examples section to include getting the Relay-reply all the way back to Relay1.

Thanks. Yes, I just added a sentence to complete the whole thing in my updated
draft in 08.txt.

BTW, for the length=0 part, one more note:-)
I initially was going to do that, but when I implemented this draft in the
ISC DHCP code base, I found that the DHCPv6 option does not support
variable size structure;-) and I also searched for all the other v6 options,
none of them are variable sized; thus the choice to use fixed size and
make the ‘downstream port’ = 0 is the choice. just FYI.

thanks.
- Naiming

> 
> Your answers for the other two points seem reasonable.
> 
> Thanks!
> 
> /a
> 
> On 11/28/17 8:00 PM, Naiming Shen (naiming) wrote:
>> Hi Adam,
>> 
>> Thanks for the comments, replies inline <NS> … </NS>
>> 
>>> On Nov 28, 2017, at 5:30 PM, Adam Roach <[e-mail]> wrote:
>>> 
>>> Adam Roach has entered the following ballot position for
>>> draft-ietf-dhc-relay-port-07: No Objection
>>> 
>>> When responding, please keep the subject line intact and reply to all
>>> email addresses included in the To and CC lines. (Feel free to cut this
>>> introductory paragraph, however.)
>>> 
>>> 
>>> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
>>> for more information about IESG DISCUSS and COMMENT positions.
>>> 
>>> 
>>> The document, along with other ballot positions, can be found here:
>>> https://datatracker.ietf.org/doc/draft-ietf-dhc-relay-port/
>>> 
>>> 
>>> 
>>> ----------------------------------------------------------------------
>>> COMMENT:
>>> ----------------------------------------------------------------------
>>> 
>>> Thanks for your time on this document. I have one minor correction and two
>>> questions.
>>> 
>>> The introduction says: "...for IPv6 the server port is (546) and the client
>>> port is (547)."  I believe this is backwards.
>>> 
>> Yes. Will fix.
>> 
>>> Section 5.2 says:
>>> 
>>>   If this option is included to
>>>   indicate only the local non-DHCP UDP port usage and there is no
>>>   downstream relay agent's non-DHCP UDP port usage, the field
>>>   Downstream Source Port field MUST be set to zero.
>>> 
>>> Was the use of length=0 considered rather that port=0 here? The reason I ask is
>>> that UDP port 0 is *reserved*, but not technically *invalid*, and the use of
>>> "length=0" would distinguish between the flag usage and the port usage while
>>> not precluding the valid (if admittedly rare) use of port=0.
>>> 
>> Although it’s valid, but should not be used. Or here this draft saying an
>> alternative relay-port is a non-zero number. Will mention that.
>> 
>>> Finally, I have a question about DHCPv6 relay agent chains that arose in
>>> reading the document. The example section actually gives a pretty good jumping
>>> off point to ask the question, so I'll quote an excerpt here:
>>> 
>>>   Similar to the above example, now assume that Relay2 uses the UDP
>>>   source port of 2000 instead of 547 as in the diagram.  The Relay3
>>>   device needs to support this DHCP extension and it will set 2000 in
>>>   its "Downstream Source Port" field of the option in the Relay-forward
>>>   message.  When DHCP server sends the DHCP Relay-reply to Relay3,
>>>   Relay3 finds its own relay option has this "Downstream Source Port"
>>>   with the value of 2000.  Relay3 will use this UDP port when sending
>>>   the Relay-reply message to Relay2.
>>> 
>>> If we were to continue this paragraph all the way back to Relay1, it's not
>>> clear how Relay2 would know to use port 1000 when sending its Relay-reply
>>> message to Relay1. Does this mechanism have a limitation that only one Relay
>>> Agent in the forwarding chain is allowed to use a Non-DHCP UDP Port?
>>> 
>> No, there is no limitation on how many relay-agents in the chain to use the Non-DHCP
>> UDP port.
>> 
>> The rule is that, a relay-agent needs to use this relay-port option either
>> this agent itself uses a Non-DHCP port, or it’s downstream agent uses
>> a Non-DHCP port.
>> 
>> So, in the above example quoted,
>> - Relay1 will include the relay-port option in its relay-forward message
>> - Relay2 will include the relay-port option (also set the downstream port to 1000) in
>>   ins relay-forward message
>> 
>> when the relay-relay message comes to Relay2, it checks it’s own
>> relay-port option is included, and it gets the 1000 port number to use.
>> this is no different when Relay2 itself does not use a Non-DHCP port.
>> 
>> thanks.
>> - Naiming
>> 
>