ssh-agent use in different security domains

[Alan Barrett]

On Fri, 24 Feb 2012, Saku Ytti wrote:
> I just had discussion about another usage case for ssh agent 
> forwarding, which I'm not sure ProxyCommand can fix, am I 
> missing something, or is there after all usage case for agent 
> forwarding?
  [...]
>With agent forwarding you could do
>a% ssh b ssh c scp file d:

With ProxyCommand, you'd just do:
a% ssh c scp file d:

and the intermediate step of hopping through b would be handled by 
a ProxyCommand setting in your .ssh/config file:

    Host c
        ProxyCommand ssh -W %h:%p b

--apb (Alan Barrett)