Iljitsch,
On Aug 4, 2009, at 05:24 MDT, Iljitsch van Beijnum wrote:
On 30 jul 2009, at 18:49, Margaret Wasserman wrote:
We need to consider what will happen if one of these packets is
received by a non-LISP node. Are you assuming that non-LISP stacks
will simply throw away these packets, because they have zero (and
therefore invalid) UDP checksums? That's only a good assumption if
we assume that LISP is the _only_ protocol that will allow the use
of zero checksums.
The logic behind the UDP header in LISP is to allow effective ECMP
load balancing. In IPv6 you don't need a UDP header for that,
because you can hash on the flow label rather than port numbers. So
no need for a UDP header -> no 0 checksums with LISP over IPv6.
The above assumes that a host actually imposes a flow-label on
outgoing IPv6 packets. My understanding is that the flow-label isn't
widely (if at all?) implemented, by default, in hosts; however, I
would welcome corrections in my understanding with a list of host
implementations that have the flow-label enabled by default.
Second, I'll check around some more, but with respect to most routers
I'm familiar with (particularly, MPLS LSR's that will be carrying IPv6
over MPLS inside a SP's ASN), they *also* don't use the IPv6 flow-
label as an input key to calculate a hash to determine the outgoing
component-link. However, they *do* currently use the Source and
Destination Ports of the Transport Layer protocol as input keys to
calculate a hash-key to determine the outgoing component-link/path.
Since I don't work at these router vendors I can't explain the
rationale for not using the flow-label as an input key to an ECMP or
LAG load-balancing hash; however, I would suspect that if the flow-
label isn't well-defined nor is it widely implemented in hosts, then
it makes no sense for router vendors to try to include it in their
hash-algorithms for ECMP/LAG load-balancing.
So, in summary, I support UDP/IPvX encapsulation for LISP, (and other
similar protocols that may appear as "macro-flows" in the core of a
network), as it's the only well-known method, available today, for
achieving load-balancing across ECMP or LAG paths that are widely
deployed in today's networks and will continue to exist forever, (even
with 100GE "just around the corner").
-shane
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