Re: [lisp] Review of RFC6833bis

[Dino Farinacci <[e-mail]>]

> Hi all,
> 
> Wanted to send this before the meeting on Friday. I just completed a
> review of 6833bis, you can find my comments below. Like last time,
> extracts from the draft are copied and followed by my comments.
> 
> Thanks,
> Alberto

Thanks again Alberto for your comments. See my responses inline and a -07 diff file.

> Map-Resolver:  A network infrastructure component that accepts LISP
> Encapsulated Map-Requests,
> 
>    • [AR] We could remove "Encapsulated" and just use "Map-Requests".
> A Map-Resolver may accept non-encapsulated Map-Requests as well.

No, they are “control-plane” encapsulated. I’ll make that more clear.

> Map-Register message:   A LISP message sent by an ETR to a Map-Server
> to register its associated EID-Prefixes.  In addition to the set of
> EID-Prefixes to register, the message includes one or more RLOCs to be
> used by the Map-Server when forwarding Map-Requests (re-formatted as
> Encapsulated Map-Requests) received through the database mapping
> system.
> 
>    • [AR] This may give the impression that the RLOCs on the
> Map-Register are only to forward Map-Requests, which is not the case
> in proxy-reply mode. I would suggest we rephrase this text as follows:
> "In addition to the set of EID-Prefixes to register, the message
> includes one or more RLOCs to be used to reach the ETR. The Map-Server
> uses these RLOCs when it has to forward Map-Requests (potentially
> re-formatted as Encapsulated Map-Requests) received through the
> database mapping system.”

I reworded. 

> Map-Notify message:   A LISP message sent by a Map-Server to an ETR
> 
>    • [AR] I would replace "ETR" with "xTR" so we cover the PubSub
> behavior as well.

Can’t do that because an ITR does not get Map-Notifies as a response to a Map-Register. But I will add that ITRs get Map-Notifies to inform them of RLOC-set changes (for pubsub and signal-free-multicast use-cases).

> 
> For definitions of other terms -- notably Map-Request, Map-Reply,
> Ingress Tunnel Router (ITR), and Egress Tunnel Router (ETR) -- please
> consult the LISP specification [I-D.ietf-lisp-rfc6830bis].
> 
>    • [AR] I think that the definitions for Map-Request and Map-Reply
> should be moved here, and probably we should include the definition
> for Map-Notify-Ack as well. 6830bis should reference 6833bis for
> control-plane messages, not the other way around.

They did. But the text you identified above was not changed. Changed now.
 
> A Map-Register message contains a list of EID-Prefixes plus a set of
> RLOCs that can be used to reach the ETR when a Map-Server needs to
> forward a Map-Request to it.
> 
>    • [AR] Since proxy-reply is a common case, I'd not constrain the
> meaning of the RLOCs in the Map-Register. I'd remove the last part of
> the sentence that says "when a Map-Server needs to forward a
> Map-Request to it.”

Agree.

> A Map-Resolver receives Encapsulated Map-Requests from its client ITRs
> and uses a mapping database system to find the appropriate ETR to
> answer those requests.
> 
>    • [AR] A MR can receive Map-Requests that don't come from ITR
> and/or that are not encapsulated. If we don't want to change the text,
> at least I'd add at the beginning: "In a common scenario, a
> Map-Resolver…"

I don’t think we should change this. The lig document indicates that a lig client can send Map-Requests. This document is for support of a data-plane.

> Note that while it is conceivable that a non-LISP-DDT Map-Resolver
> could cache responses to improve performance,
> 
>    • [AR] The discussion on caching or not at the Map-Resolver goes
> beyond DDT. We could rephrase this removing the mention to
> "non-LISP-DDT”.

Agree. Changed.

> The LISP UDP-based messages are the Map-Request and Map-Reply
> messages.  When a UDP Map-Request is sent, the UDP source port is
> chosen by the sender and the destination UDP port number is set to
> 4342.  When a UDP Map-Reply is sent, the source UDP port number is set
> to 4342 and the destination UDP port number is copied from the source
> port of either the Map-Request or the invoking data packet.
> 
>    • [AR] I would remove the first sentence and re-phrase this
> paragraph as follows: "When a UDP LISP control message is sent and is
> not a direct reply to a previous control message, the UDP source port
> is chosen by the sender and the destination UDP port number is set to
> 4342.  When a UDP LISP control message is sent as a direct reply to a
> previous message, the source UDP port number is set to 4342 and the
> destination UDP port number is either set to 4342 or copied from the
> source port of the invoking LISP control message. See the following
> subsections for details.”

This is not really true. There are too many cases with respect to NAT-traversal that make things more complicated. I think we need to be specific about each message and not generalize it. Plus, Map-Notify messages are response and unsolicited so they vary on whether the destination or source port is 4342. 

I have added text to identify each message that follow the Map-Request and Map-Reply port rules.

> The UDP checksum is computed and set to non-zero for Map-Request,
> Map-Reply, Map-Register, and Encapsulated Control Message (ECM)
> control messages.
> 
>    • [AR] Shouldn't it be computed for all LISP control messages?

Yes. Added text.

> EID-Prefix:  This prefix is 4 octets for an IPv4 address family and 16
> octets for an IPv6 address family.  When a Map-Request is sent by an
> ITR because a data packet is received for a destination where there is
> no mapping entry, the EID-Prefix is set to the destination IP address
> of the data packet, and the 'EID mask-len' is set to 32 or 128 for
> IPv4 or IPv6, respectively.
> 
>    • [AR] We should probably rephrase this to don't limit it to IPv4/6

Good point. Generalized the text a bit.

> For the latter two cases, the destination IP address used for the
> Map-Request is one of the RLOC addresses from the Locator-Set of the
> Map-Cache entry.
> 
>    • [AR] To refresh map-caches before TTL expiration, the
> destination IP of the Map-Request can be the address of the Map-Server
> if in proxy-reply. This should be considered here.

This is not true. The Map-Request has an IP header but it is encapsulated in an ECM and that IP header destination address is the *Map-Resolvers*.

> If the ITR erroneously provides no ITR-RLOC addresses, the Map-Replier
> MUST drop the Map-Request.
> 
>    • [AR] This could probably be a SHOULD since we use AFI = 0 as
> ITR-RLOC to unsubscribe in PubSub.

An AFI=0 Is an RLOC address.

> EID-Prefix:  This prefix is 4 octets for an IPv4 address family and 16
> octets for an IPv6 address family.
> 
>    • [AR] We should mention the possibility for address families
> other than IPv4/6.

Have that covered.

> The RLOCs in the Map-Reply are globally routable IP addresses of all
> ETRs for the LISP site.
> 
>    • [AR] We should remove "globally" here. Maybe also add a
> "Generally" at the beginning since we might have LCAFs with AFI = 0
> (LISP-VPN encoding of Home-IID for instance).

Removed “globally”. I don’t understand your other “Generally” comment.

> For example, a requester with two cached EID-Prefixes that are covered
> by a Map-Reply containing one less-specific prefix replaces the entry
> with the less-specific EID-Prefix.
> 
>    • [AR] Not sure if I follow here. Does this mean that a
> less-specific received in a Map-Reply will erase from the map-cache
> previously cached more-specifics that are covered by the
> less-specific?

Yes, because if the Map-Reply returned a more-specific with the less-specific, then it would be replaced so the less-specific replaces the more-specifics that ARE NOT in the Map-Reply.

> When more than one EID-Prefix is returned, all SHOULD use the same
> Time to Live value so they can all time out at the same time.  When a
> more-specific EID-Prefix is received later, its Time to Live value in
> the Map-Reply record can be stored even when other less-specific
> entries exist.
> 
>    • [AR] We should explain in which cases a more-specific can be
> received later.

I don’t follow. Each EID-record will contain a TTL for the length prefix that is encoded. So the new Map-Reply TTL will be used for any length entry (and in this case the more-specific).

> The Locator-Set MUST be sorted in order of ascending IP address where
> an IPv4 locator address is considered numerically 'less than' an IPv6
> locator address.
> 
>    • [AR] LCAF addresses (maybe with AFI=0) should be discussed here as well.

It is discussed in the LCAF draft. Don’t want to repeat it.

> Nonce:  This 8-octet 'Nonce' field is set to 0 in Map-Register messages.
> 
>    • [AR] Since there may be future cases that benefit from having a
> non-zero nonce on the Map-Register, I would suggest to rephrase this
> sentence to add a CAN.

Not until we identify and describe the use-case. No point to speculate. But note, if a Map-Notify is returned, the nonce should be non-zero. I’ll fix that.

> E:  This is the to-ETR bit.  When set to 1, the Map-Server's intention
> is to forward the ECM to an authoritative ETR.
> 
>    • [AR] Can M and E be set at the same time?

It can. M bit is set to indicate to avoid DDT procedures. The E bit tells the Map-Server what to do with the Map-Request.

> LCM:  The format is one of the control message formats described in
> this section.  At this time, only Map-Request messages are allowed to
> be encapsulated.
> 
>    • [AR] Shall we mention the NAT traversal draft?

No, this is an ECM, not a data-encapsulated control-message.

> A Map-Server's configuration must also include a list of the
> EID-Prefixes for which each ETR is authoritative.
> 
>    • [AR] There may be certain cases where this does not need to be
> pre-configured. I suggest we replace the "must" with a "should". Note
> that this requirement is already a "should" in section 6.

Agree.

> See [I-D.ietf-lisp-rfc6830bis] for details on how the Map-Server sets
> certain flags (such as those indicating whether the message is
> authoritative and how returned Locators should be treated) when
> sending a Map-Reply on behalf of an ETR.
> 
>    • [AR] It may be useful to discuss at least some of those details here.

It does following this.

I also made the document RFC2119 compliant where the terms for not capitalized. There were a few places.

Thanks again,
Dino