[rrg] Locator Path Liveness concerns

[RJ Atkinson]

On  9 Dec 2008, at 09:08, Scott Brim wrote:
> Excerpts from RJ Atkinson at 09:00:09 -0500 on Tue  9 Dec 2008:
>> Off the top of my head, it seems to me that this issue already exists
>> in the deployed IPv4 Internet and also in the deployed IPv6 Internet.
>>
>> If one considers a multi-homed end-system (i.e. one that is
>> directly connected to multiple IP subnetworks), that host needs
>> to make a decision about which source IP address to use
>> to communicate.
>>
>> If it is communicating with a remote node that is also multi-homed
>> (same definition), then it needs to make a decision about which
>> destination IP address to use to communicate (typically this is
>> a choice from the set of A/AAAA records that the first host found
>> in the DNS for the remote node).
>>
>> Few multi-homed hosts participate in intra-domain routing.
>> Fewer participate in inter-domain routing.  So nearly all hosts
>> wanting to correspond cannot use knowledge from the routing
>> system to make a better informed decision about either the
>> source address to use or the destination address to use.
>
> This is a good point -- individual devices that are multihomed already
> face that situation.  Is there any deployed use of multiple
> simultaneous paths?

We should all think about that question.

A quick answer is that at least deployments of applications
using SCTP will use multiple paths today.  A basic multi-path
multi-homing capability has been in SCTP all along.  More
recently, dynamic multi-homing capability has been added.
If I understood my namesake when I last chatted with him,
SCTP's dynamic multi-homing capability has multiple independent
implementations already.

SCTP is not the most widely used transport protocol.
However, it is deployed and it has real-world use today.
I am reliably told that the multi-homing capability is
critical to most currently deployed uses of SCTP.

I am also mindful of Mark Handley's proposal for a multi-homed,
multi-path TCP extension.  Such an extension seems sensible to me,
at least conceptually, particularly given that there are now
experimental results from SCTP indicating that such a thing
can work reasonably well.

> What is new is the opportunity to do something more with it given
> locator/identifier separation.

Hmm.  I'm not quite sure.

> "Here's this cool new tool, but to use
> it you have to install new wiring in your house and by the way your
> electric bill will double."

(I haven't finished my coffee yet, so maybe it is just me,
but I have no idea what that quoted text means. :-)

Cheers,

Ran
rja at extremenetworks.com