Re: Shim6 failure recovery after garbage collection

[Joe Abley <jabley@isc.org>]

On 17-Apr-2006, at 19:03, Erik Nordmark wrote:

> Taking a step back, why do we think that having a few bytes of  
> shim6 context on the server as a problem? A http server is likely  
> to have many TCP connections in TIME_WAIT state for every client IP  
> address, but it will have at most one shim6 context state.

One of the more comprehensible objections to shim6 that was raised at  
NANOG 35 was from large content providers who currently serve many  
thousands of simultaneous clients through load balancers or other  
content-aggregation devices (the kind of devices which switch  
connections to origin servers without having to store any locally).

I don't remember the precise number of simultaneous sessions the  
devices were intended to be capable of serving, but it was a lot.

The observation was that with the amount of (server, client) state  
being held on those devices, adding what might be an average of (say)  
2x128 bits + misc overhead per session might present scaling  
difficulties.

> And with TCP a shim6 implementation can probably discard the shim6  
> state when the last TCP socket closes (i.e. long before the  
> TIME_WAIT connections can be discarded).

I hear what you are saying.

Perhaps Igor or Patrick could comment on likely numbers of (server,  
client) state required (perhaps excluding sessions in TIME_WAIT) in  
their experience -- with actual numbers, the scale of the issue might  
be more apparent.


Joe