Re: [lisp] 6830bis Review

[Luigi Iannone <[e-mail]>]

HI Albert,

thanks for your reply. 

My comments inline. (trimming what is OK for me)

Luigi

> On 27 Dec 2017, at 02:48, Albert Cabellos <[e-mail] <mailto:[e-mail]>> wrote:
> 

[snip]
> >
> >
> >   Endpoint ID (EID):   An EID is a 32-bit (for IPv4) or 128-bit (for
> >      IPv6) value used in the source and destination address fields of
> >      the first (most inner) LISP header of a packet.  The host obtains
> >      a destination EID the same way it obtains a destination address
> >      today, for example, through a Domain Name System (DNS) [RFC1034]
> >      lookup or Session Initiation Protocol (SIP) [RFC3261] exchange.
> >      The source EID is obtained via existing mechanisms used to set a
> >      host's "local" IP address.  An EID used on the public Internet
> >      must have the same properties as any other IP address used in that
> >      manner; this means, among other things, that it must be globally
> >      unique.  An EID is allocated to a host from an EID-Prefix block
> >      associated with the site where the host is located.  An EID can be
> >      used by a host to refer to other hosts.  Note that EID blocks MAY
> >      be assigned in a hierarchical manner, independent of the network
> >      topology, to facilitate scaling of the mapping database.  In
> >      addition, an EID block assigned to a site may have site-local
> >      structure (subnetting) for routing within the site; this structure
> >      is not visible to the global routing system.  In theory, the bit
> >      string that represents an EID for one device can represent an RLOC
> >      for a different device.  As the architecture is realized, if a
> >      given bit string is both an RLOC and an EID, it must refer to the
> >      same entity in both cases.
> >
> >
> > Is the above sentence really necessary?
> >
> 
> Agreed, why not simplify the definitions. They are written from the ‘Internet scalability mindset’, why not say that an EID is an address of the overlay and an RLOC an address of the overlay. This change may require further changes on the document so I am not 100% sure if this is a good idea.

For clarification I was just referring to the sentence:

 " As the architecture is realized, if a given bit string is both an RLOC and an EID, it must refer to the same entity in both cases.” 

I am wondering if such constrain is really necessary. If namespaces are well scoped there is no need for this. 

[snip]

About the following:

> 
> >
> >   o  EIDs are typically IP addresses assigned to hosts.
> >
> >   o  Other types of EID are supported by LISP, see [RFC8060] for
> >      further information.
> >
> > I would put the last two bullets in the definition of EID. It simplifies the story here.
> >
> >
> 
> I suggest to leave them here, I don´t think that readers start from the ‘Definition of terms’, these are relevant concepts to understand LISP.

Good point about de definition of terms. What really bothers me is the bullet organisation. What can be done is to merge these two bullets with the previous one. 

> 
> >
> > The description of the encap/decap operation lacks of clarity concerning how to deal with
> > ECN bits and DSCP .
> >
> > 1. I think that the text should make explicitly the difference between DSCP and ECN fields.
> >
> > 2. How to deal with ECN should be part of the description of the  encap/decap not a paragraph apart.
> >    This basically means that half of the last paragraph should be a bullet of the ITR/PITR encapsulation
> >    and the other half  in the ETR/PETR operation.
> 
> 
> Agreed, what about this (please comment):
> 
>    When doing ITR/PITR encapsulation:
> 
>     o  The outer-header 'Time to Live' field (or 'Hop Limit' field, in the case of IPv6) SHOULD be copied from the inner-header 'Time to Live' field.
>     o  The outer-header 'Differentiated Services Code Point' (DSCP) field (or the 'Traffic Class' field, in the case of IPv6) SHOULD be copied from the inner-header DSCP field ('Traffic Class' field, in the case of IPv6) considering the exception listed below.
>    o  The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7 of the IPv6 'Traffic Class' field) requires special treatment in order to avoid discarding indications of congestion [RFC3168]. ITR encapsulation MUST copy the 2-bit 'ECN' field from the inner header to the outer header. Re-encapsulation MUST copy the 2-bit 'ECN' field from the stripped outer header to the new outer header.
> 
> When doing ETR/PETR decapsulation:
> 
>    o  The inner-header 'Time to Live' field (or 'Hop Limit' field, in the case of IPv6) SHOULD be copied from the outer-header 'Time to Live' field, when the Time to Live value of the outer header is less than the Time to Live value of the inner header.  Failing to perform this check can cause the Time to Live of the inner header to increment across encapsulation/decapsulation cycles.  This check is also performed when doing initial encapsulation, when a packet comes to an ITR or PITR destined for a LISP site.
>    o  The inner-header 'Differentiated Services Code Point' (DSCP) field (or the 'Traffic Class' field, in the case of IPv6) SHOULD be copied from the outer-header DSCP field ('Traffic Class' field, in the case of IPv6) considering the exception listed below.
>    o  The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7 of the IPv6 'Traffic Class' field) requires special treatment in order to avoid discarding indications of congestion [RFC3168]. If the 'ECN' field contains a congestion indication codepoint (the value is '11', the Congestion Experienced (CE) codepoint), then ETR decapsulation MUST copy the 2-bit 'ECN' field from the stripped outer header to the surviving inner header that is used to forward the packet beyond the ETR.  These requirements preserve CE indications when a packet that uses ECN traverses a LISP tunnel and becomes marked with a CE indication due to congestion between the tunnel endpoints.
> 
> Note that if an ETR/PETR is also an ITR/PITR and chooses to re-encapsulate after decapsulating, the net effect of this is that the new outer header will carry the same Time to Live as the old outer header minus 1.
> 
> Copying the Time to Live (TTL) serves two purposes: first, it preserves the distance the host intended the packet to travel; second, and more importantly, it provides for suppression of looping packets in the event there is a loop of concatenated tunnels due to misconfiguration.  See Section 18.3 for TTL exception handling for traceroute packets.
> 

Text looks very good to me.


> 
> >
> > Large part of this section is about control plane issues and as such should be put in 6833bis.
> >
> > What this section should state is that priority and weight are used to select the RLOC to use.
> > Only exception is gleaning where we have one single RLOC and we do not know neither priority nor weight.
> >
> > All the other operational discussion goes elsewhere, but not in this document.
> >
> 
> Agree, I suggest moving it to 6833bis. What to leave in 6830bis is less obvious, maybe something like (not final, just a couple of ideas):
> 
> The data-plane must follow the state stored in the map-cache to encapsulate and decapsulate packets. The map-cache is populated using a control-plane, such as [6833bis]. ETRs encapsulate packets following the Priorities and Weights stored in the map-cache.
> 

Yes, this is what I meant.


> Actually we should merge this section with 'Routing Locator Hashing'
> 
> 

I think is a good idea.

[snip]
> > 13.  Changing the Contents of EID-to-RLOC Mappings
> >
> >
> > This is a control plane issue, as such it has to go in 6833bis, with two exception:
> > The very first paragraph stetting the problem, and the versioning subsection, because it is a data-plane mechanism.
> >
> > All of the rest 6833bis
> >
> > Actually I remember a suggestion about putting operations issues like this in an OAM document which would be a good idea.
> >
> >
> 
> So you are suggesting that the LISP control-plane does not define any mechanism to update EID-to-RLOC mappings? 
> 

Not exactly. Control-plane should discuss how to change the mappings, but things like clock sweep is just management not a control plane mechanism, as such it does not really needs to be standardised because there are no interoperability issues, hence it make really sense  to put it elsewhere.

Thanks

Luigi