Re: [v6ops] source address failover [PI [ULA draft revision #2 Regarding isolated networks]]

[Brian E Carpenter <[e-mail]>]

On 03/06/2014 08:47, Gert Doering wrote:
> Hi,
> 
> On Tue, Jun 03, 2014 at 08:42:55AM +1200, Brian E Carpenter wrote:
>> On 02/06/2014 20:17, Gert Doering wrote:
>> ...
>>> OTOH, proper source address failover on "host" to source address B would
>>> very nicely solve this whole category of connectivity issues - and (by
>>> enforcing halfway symmetric return traffic via ISP B) would actually solve
>>> it *better* than BGP routing, which might need manual fiddling with the
>>> router to remove "ISP C" from the path.
>> I know that shim6 isn't popular around here, but if you actually
>> want to achieve this effect - for any transport protocol, and
>> any application protocol, unmodified - run linshim6 at both ends.
> 
> I've heard very good results about failover tests with shim6 (much faster
> convergence than BGP).  
> 
> I'm not convinced we particularily *need* it, though, as - as far as I 
> understood - shim6 will primarily serve to ensure session survivability, 
> while in most scenarios, sessions are so shortlived that "oh, ISP broken,
> use other one" will be a matter of clicking reload in the browser...
> 
> Or will it also take care of selective non-reachability at session setup
> ("something in the ISP A path to Z broken")?
>

No. One of the design features of shim6 is *not* to create any
overhead for short-lived sessions, which means that by definition
it only wakes up after the first packets of a session have flowed.

I think that there are some very interesting ideas in shim6, but
it could be that it needs some redesign at this point in history,
espicially given the experience and thinking around MPTCP
and Happy Eyeballs.

    Brian