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

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

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
> 
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> 
> ----------------------------------------------------------------------
> 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

>