On Jan 9, 2018, at 7:04 AM, Luigi Iannone <[email protected]> wrote:
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 <[email protected]> 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
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