Re: [pcp] PCP proxying / relaying

[Francis Dupont <[e-mail]>]

 In your previous mail you wrote:

   This seems quite similar to how today's ALGs function.  Can this be modeled
   in the CPE router like an ALG?
   
=> if you extend the ALG notion for NATs to routers it would be an ALG.

   A difference from a normal ALG is that sometimes a PCP response needs to be

=> normal ALG? an ALG can do anything: it is supposed to have access
to all functions (in a traditional OS it is at least in part in the kernel (*)).

   generated by the CPE router itself (rather than forwarding the request to
   the upstream PCP server).  But perhaps that is why the earlier PCP Proxy
   paper (draft-bpw-pcp-proxy-00) mentioned 'faking' a response.
   
=> yes, the word 'fake' meant the response is built directly by the proxy
(which at the difference of an ALG is a standard application: its only
complexity is that it is multiplexed on two sides: the internal where it
acts as a server, the external where it acts as a client. But if you don't
require it to be able to handle a zillion of messages per second it is
still a low complexity).
   
Regards

[e-mail]

PS (*): there are two standard ways to implement such an ALG:
 - fully in the kernel (not the best: kernel programming is hairy,
  a nightmare to debug and bugs are named panics :-)
 - use a hook to intercept "interesting" packets and a second one
  to reinject processed packets (BTW NATs/firewalls often provides
  such hooks which are still available in the "router mode").

PPS: in case it is not clear I think ALGs are BAD!