shim6 @ NANOG (forwarded note from John Payne)

Joe Abley jabley at
Wed Mar 1 06:47:45 UTC 2006

On 1-Mar-2006, at 01:09, Randy Bush wrote:

>> How about some actual technical complaints about shim6?
> good question.  to give such discussion a base, could you
> point us to the documents which describe how to deploy it in
> the two most common situation operators see
>   o a large multi-homed enterprise customer

There are no documents describing deployment. Probably there should be.

The general approach is presumably well-known (for those for whom it  
is not, go browse around < 
charter.html>, and perhaps in particular < 

Deployment in an enterprise is a matter of:

  (a) deploying hosts with shim6-capable stacks within the enterprise;

  (b) arranging for those hosts to receive addresses in each PA  
assignment made by each transit provider (multiple PA addresses per  
interface), e.g. using dhcp6;

  (c) optionally, perhaps, installing shim6 middleware at some  
suitable place between host and border in order to impose site policy  
or modulate locator selection by the hosts.

In the event that one provider goes away, the internal address  
assignment infrastructure doesn't need to participate in the  
traditional handwave magic IPv6 renumbering protocol; shim6-capable  
hosts talking to other shim6-capable hosts will switch locators based  
on observed failure of the dead transit provider's addresses to work;  
transport-layer sessions are hence preserved.

You will note I have glossed over several hundred minor details (and  
several hundred more not-so-minor ones). The protocols are not yet  
published; there is no known implementation.

>   o a small to medium multi-homed tier-n isp

A small-to-medium, multi-homed, tier-n ISP can get PI space from  
their RIR, and don't need to worry about shim6 at all. Ditto larger  
ISPs, up to and including the largest.

Individual ISP customers (e.g. residential users, small/home office  
users) can multi-home in the same way as hosts within an enterprise  
network. For residential users, for example, step (b) above might be  
achieved by installing two NICs, and attaching one to the cable modem  
and the other to the DSL modem; step (c) would be unnecessary.

Content providers have a different set of problems, since a server  
with N simultaneously-active clients, each with an average of M  
available locators needs to deal with N*M worth of state, which is  
presumably M times worse than the situation today.

For very large content providers, aggregating very large numbers of  
simultaneous clients through load balancers or other middleboxes,  
this is quite possibly not something that is going to be a simple  
matter of upgrading to a shim6-capable firmware release.


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