Dino -
I think we should experimentally compare ALT with other mapping
systems
before we decide whether pull-based or push-based mapping systems are
better. Dismissing push-based mapping systems without corroborating
data would be a bit premature in my opinion.
Agree.
In the absence of experimentation results, I would actually argue in
favor of push-based mapping systems based on some analytical
reasoning:
Pull-based mapping systems have two important disadvantages compared
to
push-based mapping systems:
- Performance penalty, i.e., additional propagation latencies for some
packets, and higher loss probabilities for packets that take a sub-
optimal path
- Robustness penalty due to a new online dependency on components off
the actual transmission path. (FWIW: All pull-based mapping systems
have this penalty. Mapping requests must be routed via overlay
infrastructure because the direct route is unknown at that time.)
Make note that LISP-ALT is a hybrid. It pushes EID-prefix
announcements via eBGP over an alternate topology of GRE tunnels. And
then ITRs pull the mappings by sending Map-Requests on this topology
so ETRs (who are authoritative for the mappings) can return Map-Replies.
Furthermore, I do not share your concerns regarding push-based mapping
systems: BGP is pushing routing data already today, and this works
fine. Any routing-scalability-related issues with BGP are not due to
But the BGP RIB is order 10^5 and on average (there is lots of data on
this) only 10% of that table is used in any given router.
BGP being push-based; they are due to frequent updates and a high load
for core routers. Both of these issues would go away in an address
Other reason you want to push is if all the nodes in the "push domain"
need to use the information. If they don't it is a waste of memory and
resources. BGP is used as a transport for routing information but each
node uses that information.
Make note that NERD has been called a "push" mechanism. But it
actually is requesting to receive *all mappings*.
Also, another point I want to make where I'll use the iPhone 2.0
release as an example. In 2.0, they said they had "push email". Well
from a user point of view, that means when you open your mail app, the
email is sitting there ready to be read. If in the background, there
was a periodic process to pull the email, then it still looks like push.
The point here is begging a single question:
1) Should all the mappings in the universe be in an ITR?
2) Should only the mappings for sites the ITR is currently
talking to be in the ITR?
This is the important matter. Decide on that then we can talk about
how to get the mappings where they need to be.
In conclusion: The overlay approach of ALT is certainly an
interesting
idea. But I think it would be premature to conclude that it is the
only
viable solution before we have more evidence to back this claim.
Why do you think a conclusion is being made. I haven't made any.
Anyways, this is a good discussion and glad we have moved passed the
definition of an EID.
Dino
_______________________________________________
rrg mailing list
[email protected]
http://www.irtf.org/mailman/listinfo/rrg
