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

[Adam Roach <[e-mail]>]

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.

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
>