Subject: Re: [trill] Alvaro Retana's Discuss on draft-ietf-trill-arp-optimization-06: (with DISCUSS)

From: "Alvaro Retana (aretana)" <[email-masked]>
Date: Wed, 3 Aug 2016 16:25:35 +0000

Donald:

Hi!

Thanks for your answers!  I'll clear the DISCUSS once the document is
updated.

Thanks!

Alvaro.

On 7/29/16, 7:19 PM, "Donald Eastlake" <[email-masked]> wrote:

>Hi Alvaro,
>
>On Wed, Jul 6, 2016 at 11:13 PM, Alvaro Retana <[email-masked]>
>wrote:
>> Alvaro Retana has entered the following ballot position for
>> draft-ietf-trill-arp-optimization-06: Discuss
>>
>> ...
>>
>> ----------------------------------------------------------------------
>> DISCUSS:
>> ----------------------------------------------------------------------
>>
>> I know this is an optional optimization, as described by the ³MAY²
>> in the Introduction.  However, some of the other normative language
>> is not as strong as it should be to clearly specify the required
>> behavior (if the mechanisms are being used), cause confusion, or is
>> simply out of place.
>>
>> 1. In 3.1 (Get Sender's IP/MAC Mapping Information for Non-zero IP)
>> the text says that the ³RBridge MAY use different strategies to do
>> so².  That ³MAY² contradicts the ³SHOULD² used before it, which
>> directs the RBridge to verify a duplicate address.  s/MAY/may
>
>OK.
>
>> 2. Still in 3.1: ³Šthe RBridge SHOULD verify if a duplicate IP
>> address has already been in useŠ² What are the reasons where the
>> RBridge would not verify this situation?  IOW, why is this ³SHOULD²
>> not a ³MUST²?
>
>If the network manager's philosophy is have the network behave as if
>the relevant set of end stations were on a single link and just
>believe an ARP it received, it might not do anything to try to verify
>conflicting prior attachment information.
>
>> 3. I¹m confused as to whether the APPsub-TLV is required or not.
>> The source of my confusion comes from Section 3.3 (Determine How to
>> Handle the ARP/ND Response) which says that ³R2 SHOULD initiate a
>> link state update to inform all the other RBridges of the target's
>> locationŠThe update message can be carried by an IA APPsub-TLV
>> [IA-draft]Š² This text seems to say that the APPsub-TLV SHOULD be
>> used to carry the information ‹ but text in Section 2 (IP/MAC
>> Address Mappings) sounds to me as if the use of the APPsub-TLV is
>> optional: ³If the RBridge has extracted the sender's IP/MAC address
>> pair from the received data packet (either ARP or ND), it MAY save
>> the information and use the IA APPsub-TLVŠ² Also, 3.1 and 3.2 both
>> say that an ³RBridge MAY use the IA APPsub-TLV².  And finally the
>> Security Considerations section seems to recommend using itŠ Maybe
>> it¹s just me, but please clarify.  [BTW, if it is required, then I
>> think that both the IA-draft and DirMech references should be
>> Normative.]
>
>I agree that the wording should be clarified.
>
>RBridges are interested in the nickname of the RBridge to which some
>destination address is attached, since RBridges route on nickname. This
>information can be communicated for IP addresses with IP reachability
>link state TLVs and for MAC addresses with MAC reachability link state
>TLVs (each genrally within the scope of a VLAN (or FGL)). However, for
>ARP/RARP/ND optimization, you generally want to know the MAC<->IP
>mapping which is absent with separate MAC and IP reachability.
>
>The IA APPsub-TLV is, as far as I know, the only link state data
>format that can be used to bind together the MAC and IP address(es)
>for an interface (port), as well as providing the nickname of the
>RBridge to which that interface is attached and possibly other
>information. Thus, if you are to communicate information useful to,
>for example, provide a locally created response to an ARP, you need to
>use IA APPsub-TLV.
>
>> 4. In Section 2 (IP/MAC Address Mappings) the ³MAY² in the following
>> sentence is out of place since that is already the function of the
>> confidence (as described in draft-ietf-trill-ia-appsubtlv and
>> RFC6325): ³A different confidence level MAY also be used to indicate
>> the reliability of the mapping information.²
>
>That should be a lower case "may" (or perhaps "can" or something else).
>
>> 5. In Section 3.2 (Determine How to Reply to ARP/ND), both options
>> (?) a and b say that the ³RBridge MAY take oneŠ².  If the RBridge
>> selected that option, then I think the action is no longer optional.
>> s/MAY/MUST
>
>OK.
>
>Thanks,
>Donald
>===============================
> Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
> 155 Beaver Street, Milford, MA 01757 USA
> [email-masked]