Unless we are prepared to modify the base LISP spec ETR behavior, I
would remove everything from "Note" to the end of of the quoted
paragraph from section 3.
I think it would be helpful to instead say "Such datagrams carry RLOCs
as their outer header source addresses, and EIDs as their outer header
destination addresses."
Yours,
Joel
On 6/28/2011 2:47 PM, Vince Fuller wrote:
On Fri, Jun 24, 2011 at 02:28:35PM -0400, Joel M. Halpern wrote:
If I am reading the text Alia qutoed below correctly, the text assumes
that an ETR will do something different with a map reply based on the
whether it thinks the source address is an EID.
I think this is basically indeterimnable.
More importantly, that would be an ETR behavior, which the ALT spec
can't change.
I suspect this is a case of the authors, in good faith, trying to leave
in a hook for an idea they have for the future.
However, the effect is to introduce confusion.
Can we not do that?
I am not sure if you are asking for a text change here.
The current ALT document says the following regarding the source IP address
of an ALT datagram:
- the last paragraph in section 3:
The term "ALT Datagram" is short-hand for a Map-Request or Data Probe
to be sent into or forwarded on the ALT. Note that while the outer
header Source Address of an ALT Datagram is currently expected to be
an RLOC, there may be situations (e.g. for experimentation with
caching in intermediate ALT nodes) where an EID would be used to
force a Map-Reply to be routed back through the ALT.
- first paragraph in section 5.1:
5.1. Changes to ITR behavior with LISP+ALT
As previously described, an ITR will usually use the Map Resolver
interface and will send its Map Requests to a Map Resolver. When an
ITR instead connects via tunnels and BGP to the ALT, it sends ALT
Datagrams to one of its "upstream" ALT Routers; these are sent only
to obtain new EID-to-RLOC mappings - RLOC probe and cache TTL refresh
Map-Requests are not sent on the ALT. As in basic LISP, it should
use one of its RLOCs as the source address of these queries; it
should not use a tunnel interface as the source address as doing so
will cause replies to be forwarded over the tunneled topology and may
be problematic if the tunnel interface address is not routed
throughout the ALT.
Are you saying that one of these sections needs to be changed to make it
more clear that the source IP address of an ALT datagram should, in normal
use, be an RLOC? If so, please provide suggested text; IMHO, the existing
text is rather explicit about warning that using an EID as the source of
an ALT Datagram could have undefined consequences. We do not intend for the
infrastructure to test for that situation since the cost of doing so would
be unancceptably high.
--Vince
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