Hi Simon,
On 10/07/2012 18:50, Simon Perreault wrote:
On 07/03/2012 08:24 AM, Alexey Melnikov wrote:
I found the justification for REQ-6 hard to read/understand. Why does
access to
servers being on the internal network need to go through CGN at all?
Here's the thing: the server is not on the internal network. It's on
the external network, but it is still managed by the ISP. The ISP's
network includes the internal network and some part of the external
network. Furthermore, in many cases an ISP may run multiple CGNs, so
the ISP's network is actually multiple internal networks and some part
of the external network. The servers in the external network are
operated by the ISP and "know" the internal networks (have routes to
them), and can reach them directly without translation. And since
connections from subscribers to those servers may account for a lot of
traffic, it is important to not spend NAT resources on them.
I like this longer explanation. I agree that once I understand what you
are trying to say the shorter explanation in the document makes sense.
But it is a bit cryptic. (I don't have specific suggestions, so if you
can't improve existing text, that is Ok with me.)
Now, I'm not sure how to alter the existing text to make it easier to
understand. It seems to me that all the information is there, just not
with the same order/emphasis as what I wrote above. If the above was
useful for you to understand, could you please point out in the text
below what change would have helped you understand?
REQ-6: It MUST be possible to administratively turn off translation
for specific destination addresses and/or ports.
Justification: It is common for a CGN administrator to provide
access for subscribers to servers installed in the ISP's network,
in the external realm. When such a server is able to reach the
internal realm via normal routing (which is entirely controlled by
the ISP), translation is unneeded. In that case, the CGN may
forward packets without modification, thus acting like a plain
router. This may represent an important efficiency gain.
Figure 2 illustrates this use-case.
X1:x1 X1':x1' X2:x2
+---+from X1:x1 +---+from X1:x1 +---+
| C | to X2:x2 | | to X2:x2 | S |
| l |>>>>>>>>>>>>| C |>>>>>>>>>>>>>>| e |
| i | | G | | r |
| e |<<<<<<<<<<<<| N |<<<<<<<<<<<<<<| v |
| n |from X2:x2 | |from X2:x2 | e |
| t | to X1:x1 | | to X1:x1 | r |
+---+ +---+ +---+
Figure 2: CGN pass-through
Thanks,
Simon